Workshop on Advances in High Pressure Crystallography at Large

Workshop on Advances in High Pressure Crystallography at Large Scale Facilities 3rd–7th September 2007 Wadham College, University of Oxford and Rutherford Appleton Laboratory Organised by the International Union of Crystallography Commission on High Pressure Programme and Abstract Book The workshop on Advances in High Pressure Crystallography at Large Scale Facilities is supported by www.easylab.co.uk www.oxford-diffraction.com www.mg63.com www.almax-industries.com www.tandf.co.uk www.isis.rl.ac.uk Monday 3rd September 15.00-18.00 Registration 18.15-19.15 Drinks reception 19.15-20.30 Dinner Tuesday 4th September 09.00-09.15 Welcome Session I: Elements (Chair: S. Desgreniers) 09.15-09.45 L. Dubrovinsky (BGI, Bayreuth) Iron alloys at extreme conditions: experimental evidences for body-centred-cubic phase of Fe-Ni Alloy in the Earth’s core and chemistry of Fe-Mg, Fe-Si, and Fe-C systems 09.45-10.15 Y. Akahama (Univ. of Hyogo) Exotic high-pressure structures of elements O, P and Sc 10.15-10.45 E. Gregoryanz (Univ. of Edinburgh) Rings, chains, liquid-like states, chargedensity waves and superconductivity in sulphur 10.45-11.00 Discussion 11.00-11.30 Coffee Break Session II: Theory (Chair: K. Refson) 11.30-12.00 C. Pickard (Univ. of St Andrews) Ex nihilo prediction of high pressure phases 12.00-12.30 J. S. Tse (CLS/Univ. of Saskatchewan) Electron-phonon coupling in the high pressure phase of SiH4 and SnH4 12.30-12.45 Discussion 12.45-14.15 Lunch Session III: Chemistry, Biology and Materials (Chair: M. I. McMahon) 14.15-14.45 P. F. McMillan (Univ. College London) Stable vs metastable routes to new materials via high-pressure synthesis 14.45-15.15 F. Fabbiani (ISIS Facility) Exploring polymorphism in molecular compounds using high pressure 15.15-15.45 R. Winter (Univ. of Dortmund) Exploring the configurational and free energy landscape biomolecules under extreme conditions: from lipid membranes to proteins 15.45-16.00 Discussion 16.00-16.30 Tea Break Session III: Continued …. 16.30-16.55 K. Koski (Univ. of California) Pressure and size dependent x-ray diffraction studies of silver nanoparticles 16.55-17.25 S. Tolbert (Univ. of California) Using radial diffraction to explore ultra-hard materials 17.25-17.30 Discussion 17.30-17.55 Poster orals (Chair: M. I. McMahon) P3, P5, P18, P30, P31 17.55-19.15 Poster Session I 19.15-20.15 Dinner 20.30-22.00 Informal poster session Wednesday 5th September Session IV: Water, Ice and Clathrates (Chair: D. D. Klug) 09.00-09.30 C. Salzmann (Univ. of Oxford) New phases of ice 09.30-09.55 M. Guthrie (Univ. of Edinburgh) The local structure of ice VII: Total scattering measurements 09.55-10.25 A. Goncharov (Geophysical Laboratory) Dissociative melting and superionic phase of ice at high pressure 10.25-10.40 Discussion 10.40-11.10 Coffee Break Session IV: Continued …. 11.10-11.35 T. Strässle (PSI/ETH Zurich) Pressure-induced amorphization mechanism(s) in ice Ih probed by inelastic neutron scattering techniques 11.35-12.05 H. Shimizu (Gifu Univ.) Semiconductor clathrates at high pressure 12.05-12.15 Discussion 12.15-12.45 Poster orals (Chair: M. I. McMahon) P7, P10, P13, P24, P26, P32 12.45-14.15 Lunch Session V: Inelastic Studies (Chair: C. Sanloup) 14.15-14.45 J. Badro (LMPMC, Univ. P. et M. Curie) Effect of light elements on the sound velocities in solid iron: implications for the composition of Earth’s core 14.45-15.15 A. Lazicki (LNLL) Pressure-induced loss of free-electron-like interlayer state in Li3N detected with x-ray Raman spectroscopy 15.15-15.40 I. Loa (Univ. of Edinburgh) Vibrational properties of incommensurate elemental crystal phases 15.40-15.50 Discussion 15.50-16.00 Poster orals (Chair: M. I. McMahon) P20, P25 16.00-16.30 Tea Break Session VI: Critical Phenomena (Chair: P. G. Radaelli) 16.30-17.10 M. Grosche (Univ. of Cambridge) Pressure-tuned electronic self-organisation in quantum matter 17.10-17.20 Discussion 17.20-19.15 Poster Session II 19.15-20.15 Dinner 20.30-21.30 Piano Recital by Mami Shikimori in the Holywell Music Room Thursday 6th September Session VII: Amorphous, Liquid and Non-Crystalline Studies (Chair: P. F. McMillan) 09.00-09.30 V. Brazhkin (HPI, Troitsk) AsS melt under pressure: One substance – three liquids 09.30-09.55 A. Soper (LNLL) A pressure-induced collapse of intermediate range order in amorphous red phosphorus: The importance of using synchrotron x ray diffraction and Raman spectroscopic results to constrain computationally derived amorphous structures 09.55-10.20 C. Sanloup (Univ. of Edinburgh) Structure and density of amorphous sulphur up to 100 GPa 10.20-10.30 Discussion 10.30-11.00 Coffee Break Session VIII: Facilities and Techniques (Chair: H-K. Mao) 11.00-11.25 M. Hanfland (ESRF) Single crystal diffraction at extreme pressures 11.25-11.50 B. Lavina (Univ. of Nevada) High-pressure single-crystal diffraction with synchrotron white radiation 11.50-12.15 M. Kunz (ALS) ALS beamline 12.2.2: A versatile X-ray probe for materials at extreme P-T conditions. 12.15-12.40 C. Tulk (SNS) Neutron Scattering under extreme conditions at the Spallation Neutron Source 12.40-12.50 Discussion 12.50-14.15 Lunch Session IX: Elements and Simple Systems (Chair: J. T. Tse) 14.15-14.45 M. Santoro (LENS/Univ. of Florence) A novel form of high pressure, non-molecular carbon dioxide 14.45-15.10 L. F. Lundegaard (Univ. of Edinburgh) Structural transitions in rubidium high pressure phase IV 15.10-15.40 S. Desgreniers (Univ. of Ottawa) The ε- and ζ-oxygen of oxygen - new results 15.40-16.00 Discussion 16.00-16.30 Tea Break Session IX: Continued …. 16.30-17.10 B. Johansson (Univ. of Uppsala) The actinides – A beautiful ending of the Periodic Table 17.10-17.20 Discussion 17.20-17.35 21 IUCr Congress, Osaka, Japan, August 23-31, 2008 (Chair: M. Kunz) 18.30-19.30 Drinks Reception 19.30-22.30 Conference Dinner st Friday 7th September 08.30 09.30 Leave Wadham College to travel to Rutherford Appleton Laboratory (RAL) Welcome to RAL Session X: Facilities for High Pressure Studies at RAL (Chair: M. Kunz) 09.40-10.05 M. Amboage (Diamond Light Source) I15: Extreme Conditions Beamline at Diamond Light Source 10.05-10.30 M. Tucker (ISIS Facility) High-pressure facilities at ISIS 10.30-10.40 Discussion 10.40-11.10 Coffee Break 11.10-13.00 Tours of ISIS and Diamond 13.00-14.00 Lunch Session XI: Future Perspectives and Dynamic Prospects (Chair: S. Redfern) 14.00-14.40 H.-K. Mao (Geophysical Laboratory) New opportunities in high-pressure research: small science at big facilities 14.40-15.20 N. Holmes (LNLL) Dynamic exploration of the phase diagram 15.20-15.30 Discussion Close of Workshop and transport to Oxford and Didcot Station Talk Abstracts Tuesday • Session I: Elements 10 Iron alloys at extreme conditions: Experimental evidences for body-centred-cubic phase of Fe-Ni alloy in the earth’s core and chemistry of Fe-Mg, Fe-Si, and Fe-C systems L. Dubrovinsky , N. Dubrovinskaia , O. Narygina , A. Kuznetzov , V. Prakapenka , 3,5 3,5 4,5 4 4 L. Vitos , B. Johansson , A. S. Mikhaylushkin , S. I. Simak , I. A. Abrikosov 1 1 1 1 2 2 Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany 2 CARS, University of Chicago, USA 3 Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Brinellvägen 23, SE-100 44, Stockholm, Sweden 5 4 Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden Condensed Matter Theory Group, Physics Department, Uppsala University, Box 530, SE-75121 Uppsala, Sweden Since the discovery of the Earth’s core about a century ago, the idea of iron being the dominant component of the core gained firm support from geochemical observations, seismic data, theory of geomagnetism, and high-pressure studies. Strong support for the idea of iron in the core comes from a reasonably close match between seismologically inferred sound velocities and density of the core and the measured experimental values for pure iron by shock and static compression. While studying of pure iron at multimegabar pressures draw considerable attention and have provided rich experimental data, the knowledge of the behavior and properties of Fe-Ni, Fe-Si, Fe-C alloys at conditions of the Earth’s core is still limited. We studied the iron-nickel alloy Fe0.9Ni0.1 in situ by means of the angle dispersive X-ray diffraction in internally heated diamond anvil cells (DACs) and measured its resistance as a function of pressure and temperature. We found that at pressures above 225 GPa and temperatures over 3400 K Fe0.9Ni0.1 adopts the bcc structure. Our experimental and theoretical results not only support the interpretation of shockwave data on pure iron as a solid-solid phase transition along the Hugoniot, but also suggest that iron alloys with geochemically reasonable compositions (e.g. with significant nickel, sulfur, or silicon content) adopt the bcc-structure in the Earth’s inner core. It is now generally recognized that all metals and compounds show some solubility in the solid or liquid state, but the extend of solid solubility is different in different cases. In particular, Fe and Mg are almost immiscible at ambient pressure. There is clear evidence that they do not mix even in the liquid state at ambient pressure. Different paths are exploited nowadays to synthesise alloys between immiscible elements, e.g. mechanical alloying by means of ball milling or thin film alloying using deposition techniques. In our Letter we suggest an alternative path for overcoming miscibility barrier via high-pressure alloying, a possibility of which is predicted in our ab initio calculations. In order to test theoretical predictions, and to prove a formation of alloys between immiscible elements at high pressure, a novel experimental methodology has been developed, internal electrical heating. It allows us to overcome such deficiencies of known methods as low temperature supply of external electrical heating and inhomogeneous heating of mixture of metals by lasers. In particular, we conducted successful experiments on alloying Fe, Co, and Ni with Mg. The pressure range (over 125 GPa) at which alloying experiments now become available increased about 4 to 5 times in comparison with common multi-anvil apparatuses. Tuesday • Session I: Elements 11 Exotic high-pressure structures of elements O, P and Sc Y. Akahama , H. Fujihisa , Y. Ohishi , and H. Kawamura 1 2 1 2 3 1 Graduate School of Material Science, University of Hyogo, Japan 3 National Institute of Advanced Industrial Science and Technology (AIST), Japan Japan Synchrotron Radiation Research Institute (JASRI), Japan The high-pressure behaviors of elemental materials have been of considerable interest for many years because of predicted fascinating phenomena; structure phase transitions, metallization, s-d transition and so on. We have investigated the crystal structure of elements in the multimegabar pressures range using the high-pressure powder x-ray diffraction technique with a DAC and a SRS, and observed unexpected and unique structures in high-pressure phases of oxygen, phosphorus and scandium as follows. 1) The ε phase of solid oxygen, which occurs at 10 GPa and room temperature, has unique physical properties, that is, the polychroism, the strong infrared absorption due to the stretching vibration, a collapse of magnetic long range order, the metal-insulator transition and the structure transition around 100 GPa. Though its structure was unknown for a long time, we have recently found that the structure is comprised of (O2)4 clusters and the cluster is stable up to 100 GPa. The pressure change of the cluster shape exhibited clear correlation with those of the molecular vibration. 2) Black phosphorus exhibits five-stages of structural transitions under high-pressure; A17A7-SC-intermediate(IV)-SH-BCC. The P-IV phase occurs above 107 GPa as an intermediate phase linking the simple cubic (SC) and simple hexagonal (SH) phases. This unknown structure has been determined to be an incommensurately modulated orthorhombic lattice. The modulated structure was different from those observed in halogens and chalcogens. 3) Scandium is the first of the 3d-transition elements and is often grouped with the rareearth metals. In Sc, four stages of structural transition have been observed at pressure up to 300 GPa and the crystal structure of the highest pressure phase, Sc-V, was found to be a hexagonal lattice consisting of 6-screw helical chains. A host-guest structure with an incommensurate modulation of guest atoms also came before the chain-like structure. The occurrence of the anisotropic structure suggests the importance of interaction between 3d orbitals with their nearest-neighbor atoms. In this paper, we will introduce details of these exotic high-pressure structures and time permitting we will also present our up-to-date data in the ultra-high pressure range; the extension of the feasible range of pressure for the structural study to 410 GPa, molybdenum as an example. Tuesday • Session I: Elements 12 Rings, chains, liquid-like states, charge-density waves and superconductivity in sulphur E. Gregoryanz , O. Degtyareva , C. Sanloup , M. Hanfland , M. Somayazulu , S. Scandolo , 6 7 8 4 4 G. Profeta , M. Magnitskaya , J. Kohanoff , R. J. Hemley and H. K. Mao . 1 1 1 2 3 4 5 SUPA, School of Physics and Centre for Science at Extreme Conditions, University of Edinburgh, UK 2 School of Geosciences and Centre for Science at Extreme Conditions, University of Edinburgh, UK 3 4 5 European Synchrotron Radiation Facility, Gernoble, France Geophysical Laboratory, Carnegie Insitution of Washington, USA The Abdus Salam International Centre for Theoretical Physics (ICTP) and INFM/CNR, National Simulation Centre, Trieste, Italy 6 7 CNISM,Dipartimento di Fisica, Universita degli Studi di L'Aquila, Italy 8 Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Russia Atomistic Simulation Centre, Queen's University Belfast, UK The high-pressure behaviour of sulphur has attracted attention for some 40 years because of a wide panoply of phenomena exhibited in this seemingly simple elemental system. Using in situ diffraction techniques and ab-initio calculations, we show the relationship between a family of novel chain- and ring-structured polymorphs and newly discovered liquid-like (amorphous) state. We demonstrate that charge-density wave (CDW) instability is responsible for the formation of the incommensurate modulation of the atomic lattice. We also show that the co-existence and competition between the one-dimensional CDW and the superconducting state in sulfur leads to the previously observed increase of Tc up to 17 K, which we attribute to the suppression of the CDW instability. Tuesday • Session II: Theory 13 Ex nihilo prediction of high pressure phases Chris J. Pickard , R. J. Needs 1 1 2 School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK 2 Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, UK It is an obvious goal for a full theory of the solid state to enable the prediction of the structures adopted by large collections of atoms under a variety of conditions, including high pressure. But until relatively recently it is one that has been largely avoided. I will present a strikingly simple and effective approach to the unbiased prediction of crystal structures. It is based on an initial uniform random sampling of the space of possible structures, followed by robust structural optimisation to the local enthalpy minimum of each initial structure under quantum mechanical (density functional theory) forces and stresses. [1] I will illustrate the use of this technique with applications to situations which present considerable experimental challenges. Phase III of hydrogen [2] A metastable phase of H2O [3] [1] High pressure phases of silane, C.J. Pickard and R.J. Needs, Phys. Rev. Lett. 97, 45504, (2006). [2] Structure of phase III of solid hydrogen, C. J. Pickard and R. J. Needs, Nature Physics, DOI 10.1038/nphys625 (2007). [3] When is H2O not water?, C. J. Pickard and R. J. Needs, unpublished (2007). Tuesday • Session II: Theory 14 Electron-phonon coupling in the high pressure phase of SiH4 and SnH4 John S. Tse and Yansun Yao Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada Recently, it was suggested that dense hydrogen-dominated metallic alloys, in strongly compressed Group IV hydrides, can be potential candidate materials for a high-Tc superconductor [1,2]. To investigate this possibility, first principles calculations have been performed to study the structure, electronic and transport properties of several Group III and IV hydrides. At 120 GPa, both SiH4 [3] and SnH4 [4] were found to have novel layer structures. In SiH4, the structure composed of layers of SiH4 bridged by H bonds. However in SnH4, Sn layers intercalated by ‘‘H2’’ units is found. Perturbative linear response calculations predicted strong electron-phonon couplings in both systems and that the 2D layer structure is the essential ingredient. A common feature in the vibrational spectra of these structures is the presence of soft acoustic modes in the phonon band structure. In addtion, Fermi surface nesting and Kohn anomalies that lead to very strong electronphonon coupling was identified in SnH4. Perturbative linear response calculations show that both high pressure hydrides are superconducting. The application of the Allen-Dynes modified McMillan equation using calculated electron-phonon coupling parameters show superconducting critical temperature close to 40 K and 80 K can be achieved at 120 GPa in SiH4 and SnH4, respectively. [1] [2] [3] [4] N. W. Ashcroft, Phys. Rev. Lett. 92, 187002 (2004). N. W. Ashcroft, J. Phys. Condens. Matter 16, S945 (2004). Y. Yao, J. S. Tse, Y. Ma and K. Tanaka, Europhys. Lett. 78, 37003 (2007). J. S. Tse, Y. Yao and K. Tanaka, Phys. Rev. Lett. 98, 117004 (2007). Tuesday • Session III: Chemistry, Biology and Materials 15 Stable vs metastable routes to new materials via high pressure synthesis Paul F. McMillan Department of Chemistry and Materials Chemistry Centre, University College London, 20 Gordon Street, London WC1H 0AJ, UK We use a combination of diamond anvil cell and “large volume” press techniques to synthesise new materials at high pressure and high temperature conditions, and to carry out in situ studies of their structure and properties. Our current work is focused on: (i) transition metal nitrides and carbides (high hardness; metallic; superconductors); (ii) main group nitride and oxynitride spinels (wide bandgap; high hardness); light element solids including icosahedral B6O-B6N solid solutions and both layered and dense C-N-H solids (potentially superhard materials, with variable bandgap, and potentially new intercalation reactions). We use the P and T variables to explore and “tune” both stable and metastable transformations and reactions. Chemically designed precursors are used to access a wide range of metastable states and to form composite materials. We also explore the metastably compressed amorphous state to generate new materials. Tuesday • Session III: Chemistry, Biology and Materials 16 Exploring polymorphism in molecular compounds using high pressure Francesca P. A. Fabbiani and Colin R. Pulham 1 2 1 2 STFC, Rutherford Appleton Laboratory, Chilton, UK F.P.A.Fabbiani@rl.ac.uk School of Chemistry and CSEC, The University of Edinburgh, Edinburgh, UK The importance of polymorphism and solvate formation in the crystallisation of organic compounds is widely recognised within the industrial and academic communities. Almost all recrystallization studies in the pharmaceutical industry that seek to systematically screen for polymorphism and solvate formation are performed under ambient pressure. Recent studies have demonstrated that the application of high pressure is very effective at inducing phase transitions in a range of organic compounds. However, attempts to induce polymorphism in more complex, higher melting compounds (such as pharmaceuticals) have been less successful. This is because thermal decomposition usually occurs long before the pressure-elevated melting temperature is reached. We have instead developed a technique for growing single crystals from solution at high pressure that removes excessively high temperatures and provides an opportunity to study high-pressure crystallisation from different solvent systems. Exemplified with our study on the drug piracetam, we will illustrate how this technique, in combination with ambient-pressure screening, is not only successful in identifying known polymorphs of organic molecules, but also completely new polymorphs and solvates prepared and characterised at pressures below 1.0 GPa, thereby adding a further dimension to polymorph screening of pharmaceuticals. Tuesday • Session III: Chemistry, Biology and Materials 17 Exploring the configurational and free energy landscape of biomolecules under extreme conditions: From lipid membranes to proteins Roland Winter University of Dortmund, Physical Chemistry I – Biophysical Chemistry, Otto-Hahn Straße 6, 44227 Dortmund, Germany Lipid bilayers, which provide valuable model systems for biomembranes, display a variety of polymorphic phases, depending on their molecular structure and environmental conditions, such as pH, ionic strength, temperature and pressure. By using calorimetric, spectroscopic and in particular diffraction techniques, the temperature and pressure dependent structure and phase behavior of lipid systems, differing in chain configuration and headgroup structure have been studied. Moreover, neutron small-angle scattering and two-photon excited fluorescence microscopy have been used to study the lateral organization of phase-separated lipid membranes and raft mixtures as well as the influence of peptide and protein incorporation on membrane structure and dynamics, also under high pressure conditions. Furthermore, we discuss pressure as a kinetic variable. Applying the pressure-jump relaxation technique in combination with time-resolved synchrotron X-ray diffraction, the kinetics of various lipid phase transformations was investigated, including studies of membrane fusion processes. The technique has also been applied for studying protein folding reactions. We present data on the pressure-induced un/refolding of various proteins using synchrotron X-ray scattering and Fourier-transform infrared spectroscopy, which monitor changes in the tertiary and secondary structural properties of the proteins upon pressurization or depressurization. A simple thermodynamic approach is used for studying the stability of proteins as a function of both temperature and pressure and express it as a three-dimensional free energy surface. In this regard, we take advantage of a series of different techniques in the evaluation of the conformation of the proteins and in evaluating the changes in the thermodynamic parameters upon unfolding, such as the heat capacity, enthalpy, entropy, volume, isothermal compressibility and expansivity. The results demonstrate that combined temperature-pressure dependent studies can help delineate the free energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. Finally, recent advances in using pressure for studying misfolding and aggregation (amyloidogenesis) of proteins will be discussed. Our approach reveals new insights into the pre-aggregated regime as well as mechanistic details about concurrent aggregation pathways and the differential stability of the protein aggregates. Tuesday • Session III: Chemistry, Biology and Materials 18 Pressure and size dependent x-ray diffraction studies of silver nanoparticles Kristie J. Koski , Noelle M. Drugan , Martin Kunz , and Paul Alivisatos 1 2 1 1 2 1 Department of Chemistry, University of California, Berkeley, CA 94720, USA Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA We present experimental and computational evidence that silver nanoparticles undergo a crystallographic transformation under hydrostatic pressures of a few gigapascals. We have used synchrotron x-ray diffraction at the Advanced Light Source to investigate pressure and size-dependent trends in the crystal structure of silver nanoparticles solvated in a hydrostatic medium in a diamond anvil cell. Results, supported by first principles calculations, suggest a reversible, linear, pressure-dependent rhombohedral distortion which has not been observed in bulk silver. In addition, we explore the use of silver as a high pressure probe of the internal environment of hollow nanospheres. Tuesday • Session III: Chemistry, Biology and Materials 19 Using radial diffraction to explore ultra-hard materials Sarah H. Tolbert Department of Chemistry and Biochemistry and the California NanoSystems Institute, University of California, Los Angeles, CA 90095–1569, USA The need for new mechanically robust, chemically diverse materials for industrial applications has driven the quest for the developement of new hard materials. To this end, we have successfully designed a class of ultra-incompressible, superhard materials. To date these materials includes a number of diborides based on combinations of rhenium, ruthenium, and osmium. The mechanical properties of these materials have been investigated using synchrotron radiation via traditional in situ high pressure diamond anvil cell techniques, by diffraction in the radial geometry, and by micro-indentation. These experiments reveal impressively high values of bulk modulus, high hardnesses, and some of the highest-ever measured elastically supported differential stresses. Correlations between elastically supported differential stress and hardness indicate that the radial diffraction experiment can be used to learn about anisotropy in non-cubic, hard materials. Wednesday • Session IV: Water, Ice and Clathrates 20 New phases of ice Christoph Salzmann Wadham College, Oxford University, UK Two new hydrogen ordered phases of ice have been prepared by cooling the hydrogen disordered ices V and XII under pressure. Previous attempts to unlock the geometrical frustration in hydrogen bonded structures have focused on doping with potassium hydroxide and have had success in partially increasing the hydrogen ordering in ice Ih. By doping with hydrochloric acid we have prepared ice XIII and ice XIV and analyzed their structure by powder neutron diffraction. The space group symmetries are P21/a for ice XIII and P21212 for ice XIV. The two new phases were also characterised by Raman spectroscopy and the spectroscopic differences with their hydrogen disordered counterparts are discussed. The hydrogen order/disorder phase transitions were followed at ambient pressure by neutron diffraction, Raman spectroscopy, and differential scanning calorimetry and tested for reversibility. Wednesday • Session IV: Water, Ice and Clathrates 21 The local structure of ice VII: Total scattering measurements M. Guthrie, C. L. Bull, J. Loveday, R. J. Nelmes SUPA School of Physics and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, EH9 3JZ, UK The majority of crystalline phases of ice are characterised by disordered molecular arrangements. In the case of ice VII, Rietveld refinements of neutron-diffraction data [1,2,3] give clear evidence for multi-site disorder of the oxygen atom in addition to that of the protons. The exact nature of this disorder has profound implications for our understanding of the H-bond in ice and, in particular, the mechanism of H-bond centring in ice X [4]. However, it is extremely difficult to characterise the details of the oxygen distribution using a traditional analysis of Bragg intensities, which only contain information on spatially averaged structure. Thus, a determination of the precise nature of the multi-site disorder using a crystallographic approach requires exceptionally high experimental resolution, which remains a challenge at high pressure. We have gained additional insight into the local structure of ice VII using a ‘total-scattering' approach. Here, the total scattered intensity is Fourier transformed to give total radialdistribution functions, T(r) describing the local correlations. A direct comparison of ice VII and ice VIII (the ordered phase obtained upon cooling) using this technique indicates pronounced differences in their H-bond topology, while their molecular structure is shown to be identical. This result contrasts markedly with recent ab-initio calculations [5], which found the H-bond network to be identical in both phases. Indeed, the differences we observe persist as far as the first molecular contacts. Attempts to model ice VII using simple cubic distortions of ice VIII were unsuccessful, implying that the disorder manifests itself over an extremely short length scale. This new information on the local structure of ice VII may have important consequences for models of the VII to X phase transition. [1] [2] [3] [4] [5] W. F. Kuhs et al., J. Chem Phys. 81 3612 (1984). J. D. Jorgensen and T. G. Worlton, J. Chem. Phys. 83 329 (1985). R. J. Nelmes et al., Phys. Rev. Lett. 81 2719 (1998). M. Benoit et al., Phys. Rev. Lett. 89 145501 (2002). J.-L. Kuo and M.L. Klein, J. Phys. Chem. B, 108 19634 (2004). Wednesday • Session IV: Water, Ice and Clathrates 22 Dissociative melting and superionic phase of ice at high pressure Alexander F. Goncharov Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, D.C. 20015, USA The x-ray structure factor of water, S(q) has been measured along the melting line to 57 GPa and 1500 K using focused monochromatic synchrotron radiation and laser heated diamond anvil cell. The oxygen radial distribution function, g(r) is determined from these data. S(q) and g(r) have also been calculated using first principles and classical molecular dynamics simulations. The theoretical results are in qualitative agreement with the experimental data. Above a pressure of 4 GPa the O-O structure factor is found to be very close to that of a simple soft sphere liquid, thus permitting us to determine the associated density. By comparing these results with the density of ice, also determined in this study, we find that the enthalpy of fusion (ΔHf) increases enormously along the melting line, reaching approximately 120 kJ/mole at 40 GPa (compared with 6 kJ/mole at 0 GPa), thus revealing immediate molecular dissociation of water upon melting. This behavior is consistent with the immediate molecular dissociation of water upon melting, and above 40 GPa with the presence of a superionic phase. I thank Chrystèle Sanloup, Nir Goldman, Jonathan C. Crowhurst, Sorin Bastea, Laurence E. Fried, Nicolas Guignot, Mohamed Mezouar, Yue Meng for their contributions to this work. Wednesday • Session IV: Water, Ice and Clathrates 23 Pressure-induced amorphization mechanism(s) in ice Ih probed by inelastic neutron scattering techniques Thierry Strässle and Stefan Klotz 1 1 2 Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Switzerland 2 IMPMC, Université Pierre et Marie Curie, France We employed inelastic neutron scattering techniques under pressure to elucidate the microscopic mechanism of amorphization of ice Ih when compressed beyond 1 GPa at low temperatures. Measurements of the phonon dispersion of ice in a gaz pressure cell to 0.5 GPa allowed us to derive a lattice dynamical model as a function of pressure. The resulting calculated vibrational spectrum (PDOS) was benchmarked against incoherent inelastic measurements of a powder sample pressurized in-situ to higher pressures through the amorphization. The two data sets enable us to reconstruct from the lattice dynamical model thermodynamic and elastic properties of the system as a function of pressure. We find strong softening of some of the acoustic phonon branches in agreement with the observation of a macroscopic negative Grüneisen parameter below 70 K and the negative melting line of ice Ih near room temperature. Employing the stability criteria by Born and Lindemann, we find pressure-induced amorphization to be dominantly due to mechanical melting at low temperatures and due to thermal melting at higher temperatures, respectively. Our finding of a cross-over in the mechanism of pressure-induced amorphization of ice provides a natural explanation of the pronounced relaxation phenomena observed in high-density amorphous ice (HDA) upon warming. Wednesday • Session IV: Water, Ice and Clathrates 24 Semiconductor clathrates at high pressure Hiroyasu Shimizu and Tetsuji Kume Department of Materials Science and Technology, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan, shimizu@gifu-u.ac.jp Group-IV clathrates are open-structured Si, Ge, and Sn cage-like compounds, which have received considerable attention over the past few years. In these clathrates with nanoscale cages forming three-dimensional networks, alkali and alkaline-earth guest atoms are encapsulated in the cages of the host framework which is formed by tetrahedrally bonded group-IV atoms comprised of two or three different polyhedra. An exciting property of clathrate compounds is that they provide an opportunity to systematically alter materialproperties by changing the guest atoms or by replacing some of the framework atoms with metallic species. In these clathrates, the electron-phonon and electron-electron couplings between the guest and the host are key points to understand their characteristic properties such as superconductivity, wide band-gap, high thermoelectric power (due to the behavior of phonon-glass and electron-crystal (PGEC)), and pressure stability. These couplings can be explored in part by the study of high-pressure Raman scattering through their vibrational properties of both guest atoms and the host, and by the x-ray diffraction (XRD) through their structural properties of the host and the position of guest atoms under high pressures. The most common forms of clathrates are known as type-I and type-II, which are isostructural with hydrogen-bonded H2O clathrates. The type-I structure is formed by two X20 dodecahedra and six X24 tetrakaidecahedra in a cubic unit cell connected by the facesharing manner, which can be represented by the general formula of M8X46 if host X cages are fully occupied by guest atoms (M). Recently, we have found vibrational modes of guest atoms (Ba, K, and I) in type-I Ba8Si46, Ba8Ge43, K8Si46, and I8Si44I2 and type-III Ba24Si100 and Ba24Ge100 by Raman spectroscopy, and observed some phase transitions at pressures up to 40 GPa. The interesting properties of type-I Ba8Si46 clathrates are three pressure-induced phase transitions, which were studied by Raman scattering and XRD experiments, and theoretical calculations. The first transition at 7 GPa is caused by the displacement of the guest atoms in the large Si24 cages. The second transition observed at 15 GPa (see Figure) is characterized by a large reduction of cell volume. The mechanism of this isostructural phase transition is not still understood and remains unclear. The last transition at higher pressure range is an irreversible amorphization. Amorphous In this report, we present the characteristic Ba Si 40 GPa 7 GPa 15 GPa vibrational properties of the guest atoms and Amorphous the host frameworks in typical semiconductor Ba Ge 30~40 GPa 8 GPa clathrates, Ba8Si46, Ba8Ge43, Ba24Si100, and Ba24Ge100, Amorphous and their feature are investigated by comparing Ba Si 6.5 GPa ~23 GPa with the first-principles calcu-lations. HighAmorphous pressure phase transitions have been observed Ba Ge 3.2 GPa ~22 GPa by Raman spectroscopy and XRD, and are summarized in Figure. These behavior are Summary of high-pressure phase transitions: Ba8Si46; systematically discussed by referring other PRL 90, 155503 (2003), Ba8Ge43; JAP 101, 063549, semiconductor clathrates, and in particular by Ba24Si100; PRB 71, 094108 (2005), Ba24Ge100; JAP 101, focussing the isostructural phase transition in 113531 (2007). type-I Si clathrates. We would like to thank S. Sasaki, S. Yamanaka, T. Iitaka, J.S. Tse, and A. SanMiguel for their discussions. 8 46 8 43 24 100 24 100 Wednesday • Session V: Inelastic Studies 25 Effect of light elements on the sound velocities in solid iron: Implications for the composition of earth's core J. Badro , G. Fiquet , F. Guyot , E. Gregoryanz ,F. Occelli ,D. Antonangeli , M.D'Astuto 1 1 2 2 3 4 4 2 Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, France 2 IMPMC, Université P. et M. Curie, Paris, France Lawrence Livermore National Laboratory, USA 3 SUPA, School of Physics and Centre for Science at Extreme Conditions, University of Edinburgh, UK 4 We measured compressional sound velocities in iron and its light-element alloys (FeO, FeSi, FeS, and FeS2) at high pressure by synchrotron high-resolution inelastic x-ray scattering. This data set provides a mineralogical constraint on the composition of Earth's core, and completes the previous set formed by the pressure-density systematics for these compounds. Based on the combination of these data sets and their comparison with radial seismic models, we propose an average composition model of Earth's core. We show that sulphur cannot be the only light alloying element in the core, because it cannot satisfy both the compressibility, sound velocity and while retaining a reasonable abundance based on cosmochemical models. On the other hand, the incorporation of small amounts of silicon or oxygen is compatible with geophysical observations and geochemical abundances. From our data, the inner core contains 2.3 wt% silicon or 1.6 wt% oxygen. We show that the effect of nickel is negligible, and using recent O and Si partitioning data, we build a new composite model of the inner and outer core. Our inner core model contains 2.3 wt% silicon, and our outer core model contains 2.8 wt% silicon and 5.3 wt% oxygen. This is the first compositional model based on mineral physics that is constrained by seismology and experimental petrology. Wednesday • Session V: Inelastic Studies 26 Pressure-induced loss of free-electron-like interlayer state in Li3N detected with X-ray Raman spectroscopy A. Lazicki , W. E. Pickett , C. S. Yoo , R. T. Scalettar , M. Y. Hu 2 1,2 1 2 1 3 University of California at Davis, USA Lawrence Livermore National Laboratory, USA 3 Argonne National Laboratory, USA 1 X-ray Raman spectroscopy (XRS) in a diamond anvil cell employed to study the electronic structure of ionic compound lithium nitride revealed distinct pressure-induced changes which we here explain using first-principles density functional theory. As in layered compounds graphite and the graphite intercalates, the hexagonal phases of Li3N are found to possess a free-electron-like interlayer state. The lowest-energy conduction bands are comprised of this state, which gives rise to a concentration of charge density in the interstitial regions between the crystal layers. Pressure-induced changes in and the eventual loss of the interlayer state are shown here with first principles calculations and nitrogen kedge XRS, and correlated with other observed changes in material properties. Wednesday • Session V: Inelastic Studies 27 Vibrational properties of incommensurate elemental crystal phases Ingo Loa SUPA, School of Physics and Centre for Science at Extreme Conditions, The University of Edinburgh, UK In recent years, surprisingly complex crystal structures have been discovered in the elements at high pressures. In particular, incommensurately modulated structures and incommensurate host-guest composite structures have been observed in various elements across the periodic table, e.g., Rb, Ba, Sc, Te, and I. While considerable progress has been made in determining the detailed crystal structures of the complex phases at high pressure, the mechanisms that lead to their formation and stability are not yet fully understood. Experimental data on the lattice dynamics in the complex phases will be a key ingredient to address these issues, and inelastic x-ray scattering (IXS) spectroscopy is the technique of choice to study phonons throughout the Brillouin zone on samples in diamond anvil highpressure cells. Results on the lattice dynamics in the incommensurate composite phase Rb-IV and the incommensurately modulated phase Te-III will be presented. In the case of the composite Rb-IV, two LA-like phonon branches are observed along the direction of the incommensurate wavevector, which are attributed to separate LA-type lattice vibrations in the host and guest subsystems. The sound velocities of the host and the guest have been determined as a function of pressure in the range 16.3 to 18.4 GPa, and we will demonstrate that the guest-atom chains in the composite Rb-IV structure represent a realisation of the classic monatomic linear chain model. In the modulated Te-III, a pronounced phonon anomaly is observed that will be discussed in the context of Fermi-surface nesting and Kohn anomalies. Wednesday • Session VI: Critical Phenomena 28 Pressure-tuned electronic self-organisation in quantum matter F. M. Grosche Cavendish Laboratory, Cambridge CB3 0HE, UK Electron liquids in solids offer a diverse and fertile ground for quantum selforganisation. Fine-tuning the effective interaction between the charge carriers selects between a nearly limitless multitude of low temperature states, which include many forms of magnetism, superconductivity and charge or orbital order as well as more subtle and exotic structures. Precise control over the lattice density by hydrostatic pressure is emerging as the vehicle of choice for traversing quantum matter phase diagrams. The benefits of pressure-tuning correlated systems will be illustrated by means of a number of recent examples, including magnetism and superconductivity in narrow-band f-electron compounds, pressure-tuned disorder scattering in clathrates and logarithmic Fermi-liquid breakdown in transition metal compounds. Nevertheless, pressure is still comparatively little used in this field. The characterisation of electronic order requires multi-probe studies, which in a small-volume, high-stress environment are technically demanding. Once the challenges traditionally associated with pressure – reliability, leads, sample handling – are overcome, the huge volume of parameter space spanned by the combination of pressure and magnetic field will open up for exploration and discovery. The use of high pressure in quantum matter research will be extended dramatically by transferring the miniaturisation and mechanisation attained in nano- and biotechnology into the high pressure field. The necessary techniques have already been demonstrated separately, but only the urgent requirements of fundamental research can provide the extra focus and impetus needed to bring the components together into working high pressure systems. The ability to fine-tune matter over unprecedented ranges in lattice density and magnetic field could be used to investigate some of the outstanding issues in correlated electron physics, including metallisation of Mott insulators, which could lead to new families of high-Tc superconductors, anisotropic particle-hole condensates such as orbital antiferromagnetism and Pomeranchuk instabilities, and quantum oscillations in challenging new materials. Beyond these immediately identifiable objectives waits a multitude of unknown, truly novel states of quantum matter, which only experiment can bring to light. Thursday • Session VII: Amorphous, Liquid and Non-Crystalline Studies 29 AsS melt under pressure: One substance – three liquids V. V. Brazhkin , Y. Katayama , M. V. Kondrin , T. Hattori , A. G. Lyapin and H. Saito 1 1 2 1 2 1 2 Institute for High Pressure Physics RAS, 142190 Troitsk Moscow region, Russia Japan Atomic Energy Agency (JAEA), SPring-8, 1-1-1 Kuoto, Sayo-cho, Sayo-gun, Hyogo, 679-5143, Japan 2 As distinct from widely known structural phase transitions in crystals, phase transformations in simple inorganic isotropic liquids are rather rare and remain unexplored. There are several examples of both smooth and sharp transitions in liquids at the variation of the P,T conditions, however it is unclear whether multiple phase transformations for the single liquid are possible. We present the in-situ high-temperature – high-pressure diffraction study, as well as the insitu electrical resistance study, of AsS liquid chalcogenide whose structure at normal pressure is based on As4S4 molecules. The obtained structural data point to the existence of two quite sharp transitions in the melt at compression. These transitions are accompanied by the changes in the short-range order structure and properties. The first transition from a low viscosity molecular liquid to a high viscosity polymerized liquid occurs at P~2 GPa. The second transition from a polymerized insulator liquid to a low viscosity metallic liquid occurs at P~4.8 GPa. The cooling from the molecular liquid and the metallic one leads to the crystallization of a normal pressure phase and a high pressure one, respectively, while the cooling of the AsS polymerized liquid results in the formation of a new AsS glass. Thus, AsS chalcogenide presents demonstration of multiple phase transitions in the liquid state (molecular liquid – polymerized liquid – metallic liquid) that are accompanied by the changes in the short-range order structure and bond type. It may be supposed that the occurrence of multiple phase transitions under compression is a feature common to a wide class of substances having a molecular-based structure at normal pressure. The P,T diagrams of such melts can be regarded in some respects as shifted reflections of the phase diagram of the respective crystalline state. Thursday • Session VII: Amorphous, Liquid and Non-Crystalline Studies 30 A pressure-induced collapse of intermediate range order in amorphous red phosphorus: The importance of using synchrotron x-ray diffraction and Raman spectroscopic results to constrain computationally derived amorphous structures J. M. Zaug , S. M. Clark , and A. K. Soper 1 1 2 3 Lawrence Livermore National Laboratory, Livermore, CA, 94551, USA 2 Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA 3 CCLRC Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK “Conclusive” evidence for the existence of pressure-induced polyamorphic transitions only exists for two systems: liquid phosphorus and supercooled water. As part of a search for additional occurrences we characterized a polyamorphic transition in hydrostatically compressed amorphous red phosphorus (aRP) and also developed a modified numerical procedure that is similar to developments by Eggert et al., to determine density [1]. A metastable high-pressure aRP phase was also quenched at ambient conditions. We find for example, that under ambient conditions the quenched metastable phase and the original IRO phase nominally have the same density, 2.26–2.28 g/cc. However the application of pressure decimated the degree of IRO in aRP. Inverse Monte-Carlo (IMC) analysis constrained by x-ray diffraction (obtained from a unique ultra wide aperture diamond anvil cell), density, and Raman data suggests that the transition begins with P9 cages scattered throughout a 3-coordinate covalently bonded random phosphorus atom network. At a specific pressure the periodic coherence of P9 cage volume or perhaps the interstitial void space, weakens while the random network structure uniformly collapses with hydrostatic compression. The high-pressure aRP phase exhibits a significantly less intense first strong diffraction peak (FSDP) thus indicating a reduction in IRO. Fragments of the original ambient pressure 3-coordinate structural framework exhibit similarities to Hittorf’s phosphorus, albeit with no long-range atomic order. Details concerning data collection, normalization, and analysis using constrained IMC simulations will be presented together with results from computed changes in average atomic structural parameters (bond lengths, bond angles, distribution of coordination numbers) across the pressure-induced IRO transition. [1] Eggert J. H., Weck G., Loubeyre P. and Mezouar M., Phys. Rev. B 65, 174105 (2002). This work was partially performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-Eng-48. Thursday • Session VII: Amorphous, Liquid and Non-Crystalline Studies 31 Structure and density of amorphous sulphur up to 100 GPa Chrystèle Sanloup , Eugene Gregoryanz , Olga Degtyareva , and Michael Hanfland 1 1 2 2 3 School of Geosciences and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, UK 2 SUPA, School of Physics and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, UK 3 European Synchrotron Radiation Facility, 38043 Grenoble, France The amorphous state of elemental sulphur has been observed by in situ x-ray diffraction experiments at low temperatures and high pressures. The structure factor was measured, yielding the radial distribution functions and density. This is the first time such measurements were made in the diamond anvil cell at pressures up to 100 GPa. Upon increasing pressure a structural transition in the amorphous field was observed, accompanied by a density discontinuity. These measurements show that amorphous sulphur undergoes a first order phase transition, from a low density (LDA) to a high density (HDA) amorphous state, providing an unambiguous argument to the debate on the nature of polyamorphic transitions. If compressed further at low temperatures, sulphur recrystallizes into high quality single crystals of the spiral chain structure (S-III), the newly discovered phase (S-VII), or the incommensurate superconducting phase (S-IV) depending on pressure and temperature. Although pressure-induced amorphization has been reported in a variety of compounds to our knowledge this effect was never clearly shown to happen under pressure in an elemental bulk solid, and few compounds have been demonstrated to have a liquid-like character. This first documented case of such effects in an elemental solid could be a common scenario for simple systems at extreme conditions. Thursday • Session VIII: Facilities and Techniques 32 Single crystal diffraction at extreme pressures M. Hanfland , H. Müller , K. Syassen 1 2 1 1 2 ESRF, Grenoble, France MPI für Festkörperforschung, Stuttgart, Germany Technical advances have considerably added to the utility of single crystal studies at high pressures. New ways of supporting diamond anvils, like Boehler-Almax anvils [1], have significantly increased the volume of accessible reciprocal space. Use of He as pressure transmitting medium extends substantially the practicable pressure rage. Here we will present two examples to illustrate the recent progress. In the first example single crystals of α-ET2I3 [2] were loaded in LeToullec type membrane driven diamond anvil cells, modified for Boehler-Almax anvils with He as pressure transmitting medium. Datasets with 2° rotation images were taken at various pressures to 23 GPa with a Mar image plate scanner on the ID9A beamline of the ESRF. Total rotation range was 60º. The datasets were measured at photon energy of ~30keV and integrated with XDS [3]. The α-phase of ET2I3 is stable to 13 GPa. At 13 GPa it undergoes a structural phase transition. The high pressure phase, which remains single crystalline, can be indexed with a triclinic unit cell with twice the volume than that of α-ET2I3. The transition is reversible. The second example deals with the guest host structure observed in Na at pressures above 125 GPa [4]. [1] [2] [3] [4] R. Boehler, K. DeHantsetters, High Press. Res. 24, 391 (2004). Work done in collaboration with H. Müller. W. Kabsch, J. Appl. Cryst. 26, 795 (1993). Work done in collaboration with K. Syassen. Thursday • Session VIII: Facilities and Techniques 33 High pressure single crystal diffraction with synchrotron white radiation B. Lavina , L. Borkowski , P. Dera , R. T. Downs , H. P. Liermann , M. Nicol 1 1,2 1,2 2 3 4 1 High Pressure Science and Engineering Center, University of Nevada Las Vegas, USA 2 Consortium for Advanced Radiation Sources, University of Chicago, USA 3 4 Department of Geosciences, University of Arizona, USA HPCAT, Argonne National Laboratory, Argonne, IL, USA Structural investigations at pressure higher than about 20 GPa have generally been limited to powder diffraction due to the challenging requirements of diffractometry on very small single crystals; moreover, if a reconstructive phase transition occurs, it usually transforms the sample into powder. However, whenever applicable, single crystal diffraction provides the most unambiguous structural determination, because different Bragg peaks with the same d-spacing are spatially resolved, permitting much better analysis of the space group symmetry, polyhedral compression mechanisms, as well as accurate investigations of second order phase transitions. The setup at 16BMB and 16BMD at HPCAT, APS consists of a three circle diffractometer (0 ≤ θ ≤ 30, full ω and χ rotations), equipped with energy dispersive detector. The experimental strategy for single crystal diffraction of samples loaded in DACs includes the search and centering of polychromatic peaks and data collection at a constant selected energy. Technical and computational methods to keep micrometer crystals centered on the beam of similar size during the rotations required to bring the peaks in diffraction condition will be presented. Results on the high-pressure behavior of spinel and post-spinel phases will be shown; these phases are of interest in the geosciences because they are thought to be major components of the transition zone of the earth’s mantle. The compressibility and structural behavior of 2+ hercynite, FeAl2O4, is under investigation in order to model the pressure behavior of Fe , a ubiquitous major component of spinel solid solutions. Ferrite and manganite spinels show high pressure phase transitions to the marokite (CaMn2O4) structure-type; this phase has shown signals of a phase transition [1,2] within the orthorhombic system, however analysis of the Raman and powder diffraction data cannot provide unambiguous determination of the nature of the phase transition and the new space group. Single crystals of the two phases has been loaded in DACs with a ruby crystal as a pressure standard and Ne as pressure medium. The data will be discussed with emphasis on the accuracy of experimental determinations of the lattice parameters and diffraction intensities and of the reciprocal space accessibility. Support from NSF and DOE (BES and NNSA) are gratefully acknowledged. [1] Z. Wang, S. K. Saxena, J. J. Neumeierb, J. Solid State Chem. 170, 382 (2003). [2] Z. Wang, R. T. Downs, V. Pischedda, R. Shetty, S. K. Saxena, C. S. Zha, Y. S. Zhao, D. Schiferl, A. Waskowska, Phys. Rev. B 68, 094101 (2003). Thursday • Session VIII: Facilities and Techniques 34 ALS beamline 12.2.2: A versatile X-ray probe for materials at extreme P-T conditions M. Kunz , W. A. Caldwell , E. E. Domning , S. M. Clark 1 1 1 2 2 Department of Earth and Planetary Sciences, 307 McCone Hall, University of Berkeley, Berkeley, CA 94720, USA 2 Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA-94720, USA By making use of the hard X-ray spectrum delivered by a 6 T superconducting bending magnet, beamline 12.2.2 of the Advanced Light Source, offers a variety of experimental techniques to probe material at extreme conditions of pressure and temperature [1]. The primary focus of the program is an X-ray powder diffraction station for in situ axially laser heated diamond anvil cells [2]. Double sided heating is achieved by splitting a single 50 W Nd:YLF (cw) laser into two paths and directing them through the diamond anvils of the pressure cell onto the sample with the help of two focusing lenses and X-ray transparent carbon mirrors. Good laser coupling can be attained with a laser beam focused to a size of 30 microns, a dimension which compares favourably with an X-ray spot size of ~ 10 microns obtained through a set of Kirkpatrick-Baez mirrors. Larger hot spots can be generated by defocusing the laser beam with a penalty on power density and thus maximal temperatures achieved. Temperature is measured by spectroradiometry independently from both sides by steering the image of the glowing sample into two separate spectrometers. In addition to axial heating, we also developed a system for one sided heating of a diamond anvil cell in radial diffraction geometry [3]. For this, the unsplit infra-red laser beam is focused directly from the top into a panoramic cell without using any carbon mirrors. This allows to observe changes in texture lattice strain in material in situ upon increasing temperature. In order to extract the maximal possible structural information out of a sample in a laserheated diamond anvil cell, we are also developing a monochromator scanning diffraction technique. This is aimed at samples at extreme conditions of pressure and temperature which do not fulfill the powder statistics required for powder diffraction. Such samples also cannot be moved. Our approach scans a fixed-exit Si(111) double crystal monochromator in steps of ~100 eV over an X-ray energy range between 10 and 35 keV, recording each of the subframes on a CCD camera for subsequent data reduction and analysis. First results of measurements on a MgSiO3 post-perovskite will be presented. [1] Kunz, M., MacDowell, A.A., Caldwell, W.A., Cambie, D., Celestre, R.S., Domning, E.E., Duarte, R.M., Gleason, A.E., Glossinger, J.W., Kelez, N., Plate D.W., Yu, T., Zaug, J.M., Padmore H.A., Jeanloz, R., Alivisatos, A.P., and Clark, S.M., Journal of Synchrotron Radiation 12, 650 (2005). [2] Caldwell, W.A., Kunz, M.Celestre, R. S., Domning, E. E., Walter, M.J., Walker, D., Glossinger, J., MacDowell, A.A., Padmore, H.A., Jeanloz, R. and Clark, S.M. Laser Heated Diamond Anvil Cell at the Advanced Light Source Beamline 12.2.2, Submitted to Nuclear Instruments and Methods A. [3] Kunz, M., Miyagi, L, Caldwell, W.A., & Wenk, H.-R. (2007): In situ laser heating and radial synchrotron X-ray diffraction in a diamond anvil cell. Submitted to Review of Scientific Instruments. Thursday • Session VIII: Facilities and Techniques 35 Neutron Scattering under extreme conditions at the Spallation Neutron Source Chris A. Tulk Oak Ridge National Laboratory, Oak Ridge TN USA The Spallation Neutron Source currently under construction at Oak Ridge National Laboratory in the United States has received first neutrons in the summer of 2006. The prospects for high pressure neutron diffraction are good with the completion of a dedicated high pressure user beamline this coming winter. Here the current state of the neutron instrument suite will be highlighted with particular emphasis on performance parameters of the diffraction instruments. The instrument parameters of the Spallation Neutrons And Pressure (SNAP) instrument will include a discussion of planned micro-diffraction capabilities. Specifically, recent progress in micro-focused neutron beams demonstrates that neutron diffraction from sub 100 micron samples held within ‘more standard’ opposed gem anvil cells (e.g. DACs) are feasible. Examples of single crystal neutron diffraction using microbeam prototype devices will be given. Thursday • Session IX: Elements and Simple Systems 36 A novel form of high pressure, non-molecular carbon dioxide Mario Santoro a a,b LENS, European laboratory for Non-Linear Spectroscopy, Via N. Carrara 1, I-50019, Sesto Fiorentino, Firenze, Italy b CRS-SOFT-INFM-CNR, c/o Università di Roma “La Sapienza”, I-00185, Roma, Italy A brief overview [1] will be first presented on the most recent experimental and theoretical studies on the high pressure, non-molecular, covalent, crystalline phase V of CO2, whose structure is presently believed to be similar to the trydimite polymorph of SiO2. I will then report on the recent synthesis of a non-molecular, amorphous, mainly silica-like form of CO2 [2], named a-CO2 or “a-carbonia”, in the P-T range of 300-700 K and 40-80 GPa, which was described so far only as a result of first principle simulations [3]. Demanding synchrotron x-ray diffraction measurements have been performed on this material for determining the static structure factor S(q), which compares rather well with the theoretical S(q), as obtained from the ab-initio simulated sample. The comparison shows that carbonia is mainly a silica-like material. The huge Compton background and the limited diffraction angle accessed in the experiment prevented a more quantitative determination of the local structure. On the other hand, new results of IR and Raman spectroscopy, which compare well with ab initio simulated vibrational spectra, show that carbonia is made of a mixture of tetrahedral (CO4) sites and carbonilic (CO3), partially transformed sites. Also, it will be shown that carbon in octahedral coordination by oxygen (CO6) has to be excluded in a-CO2, which in turn differs from the high pressure forms of other group IV dioxide glasses, such as a-SiO2 and a-GeO2. Finally, a reinterpretation will be proposed of the local structure of the recently discovered crystalline phase VI [4] of CO2, which has been suggested to be an octahedrally coordinated (CO6) solid and seems to be the crystalline parent of carbonia. [1] M. Santoro, and F.A. Gorelli, Chem. Soc. Rev. 5, 918 (2006). [2] M. Santoro et al., Nature 441, 857 (2006). [3] S. Serra et al., Science 284, 788 (1999). [4] V. Iota et al., Nature Materials 6, 34 (2007). Thursday • Session IX: Elements and Simple Systems 37 Structural transitions in rubidium high pressure phase IV Lars F. Lundegaard SUPA, School of Physics and Centre for Science at Extreme Conditions, University of Edinburgh, UK Although incommensurate host-guest composite structures have now been observed in a number of different elements at high pressure (K-III, Rb-IV, Sr-V, Ba-IV, As-III, Sb-II, Bi-III [1] and recently Sc-II [2-3]) there are several aspects of the Rb-IV host-guest structure that makes it unique. In particular, the transition at 16.7 GPa on pressure decrease to a structure with disordered or “melted” chains of guest atoms has been observed in no other system. The results of powder and single crystal diffraction studies of Rb-IV conducted at the ESRF and the SRS synchrotron facilities will be presented in this talk. Using high-pressure and high-temperature powder diffraction techniques, we have investigated the P-T dependence of the chain-melting transition in the temperature range 300–550 K and pressure range 16–20 GPa . The results show that the transition pressure is strongly temperature dependent, and that the disordered phase is observed to the highest temperatures. Recent technical developments, of single crystal techniques, has made it possible to extract reliable intensities from the extremely weak Rb-IV modulation reflections. The resulting data are used for a full modulated structure refinement of Rb-IV, revealing a saw-tooth shaped modulation of the guest structure, from which new information on the host-guest interactions has been extracted. Finally a few examples illustrating the advantages of high pressure single crystal techniques will be presented. [1] M. I. McMahon & R. J. Nelmes, Z. Kristallogr. 219, 742 (2004) [2] H. Fujihisa, Y. Akahama, H. Kawamura, Y. Gotoh, H. Yamawaki, M. Sakashita, S. Takeya & K. Honda, Phys. Rev. B 72, 132103 (2005). [3] M. I. McMahon, L. F. Lundegaard, C. Hejny, S. Falconi & R. J. Nelmes, Phys. Rev. B 73, 134102 (2006). Thursday • Session IX: Elements and Simple Systems 38 The ε and ζ phases of oxygen – new results Serge Desgreniers Laboratoire de physique des solides denses, Institut de physique Ottawa-Carleton, Université d’Ottawa, Ottawa, K1N 6N5, Canada Numerous theoretical, computational, and experimental studies have uncovered the breadth of physical properties for the different high-density phases of solid oxygen [1]. Recently, the ε- and ζ-oxygen phases, which exist at room temperature over a large pressure range, extending from 10.4 to 96 GPa and 96 GPa to as least 140 GPa for ε- and ζ-oxygen, respectively, have been of substantial interest. The ε-oxygen phase reveals a remarkable crystalline structure formed by the clustering of oxygen molecules into (O2)4 lattice subunits [2,3]. Compression of ε-oxygen leads to a transition to a molecular metallic phase (ζoxygen). The crystalline structure of ζ-oxygen has not been fully determined. The main goal of the present study is to shed light on the nature of the crystalline structures of both the ε- and ζ-oxygen phases. In this presentation, I report the latest results regarding the εand ζ-oxygen phases arising from X-ray diffraction and Raman spectroscopy experiments carried out at room temperature up to 140 GPa on single crystals of oxygen imbedded and oriented differently in solid helium. The successful growth of individual single crystals of oxygen in helium was based on the very low miscibility of liquid O2 in liquid He at 450K and 22.5 GPa at a concentration of 2.5 mol % of O2. In the ε-oxygen phase, experimental results clearly indicate the persistence of the clustering of oxygen molecules to high density, as predicted by recent computational studies. The ε− to ζ-oxygen phase transition is readily observed by single crystal X-ray diffraction. The most plausible crystalline structures for the ζ-oxygen phase are presented and discussed. [1] Y. A. Freiman and H. J. Jodl, Phys. Rep. 401, 1 (2004) [2] L. F. Lundegaard, G. Weck, M. I. McMahon, S. Desgreniers and P. Loubeyre, Nature 443, 201 (2006). [3] H. Fujihisa et al., Phys. Rev. Lett. 97, 085503 (2006). Thursday • Session IX: Elements and Simple Systems 39 The actinides – A beautiful ending of the periodic table Börje Johansson 1 1,2 Condensed Matter Theory Group, Department of Physics, Uppsala University, BOX 530, S-751 21, Uppsala, Sweden Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Brinellvägen 23, SE-100 44, Stockholm, Sweden 2 The 5f elements, actinides, show many properties which a have direct correspondence to the 4f transition metals, the lanthanides. The remarkable similarity between the solid state properties of compressed Ce and the actinide metals is pointed out in the present paper [1]. The α-γ transition in Ce is considered as a Mott transition, namely, from delocalized to localized 4f states. An analogous behavior is also found for the actinide series, where the sudden volume increase from Pu to Am can be viewed upon as a Mott transition within the 5f shell as a function of the atomic number Z. On the itinerant side of the Mott transition, the earlier actinides (Pa-Pu) show low symmetry structure at ambient conditions; while across the border, the heavier elements (Am-Cf) present the dhcp structure, an atomic arrangement typical for the lanthanide elements with localized 4f magnetic moments. The reason for an isostructural Mott transition of the f electron in Ce, as opposed to the much more complicated cases in the actinides, is identified. The strange appearance of the δ-phase (fcc) in the phase diagram of Pu is another consequence of the border line behavior of the 5f electrons. The path leading from δ-Pu to α-Pu is identified. [1] Börje Johansson and Sa Li, J. Alloys Comp., in press, available online 8 January 2007, doi:10.1016/j.jallcom.2006.12.111. Friday • Session X: Facilities for High Pressure Studies at RAL 40 I15: Extreme Conditions Beamline at Diamond Light Source A. P. Jephcoat, H. Wilhelm, M. Amboage, A. K. Kleppe, A. M. Ross, S. M. Scott, P. N. Denison, and G. R. Wilkin Diamond Light Source Ltd. Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK Diamond Light Source is the new 3 GeV, high brilliance, UK synchrotron. The Extreme Conditions Beamline, I15, is a multifunctional and highly flexible beamline designed to offer a range of diffraction techniques for the study of states of matter at extreme conditions of pressure and temperature. It provides both white beam into the 100 keV range from a 3.5 T superconducting wiggler and monochromatic high-energy X-rays (between 20 and 80 keV) with a purpose-built double crystal Bragg monochromator (DCM) for high heat load. Focusing is achieved by a pair of 1.2 m long KB mirrors. A second pair of 300 mm KB mirrors will ultimately be implemented based on two intermediate source points (separate horizontal and vertical virtual focus at adjustable apertures) to allow spot sizes in the 10’s microns range with high spatial/intensity stability. Angle-dispersive powder diffraction and, various implementations of single-crystal diffraction (based around a flexible Newport six-circle diffractometer) experiments will be performed over a range of pressures and temperatures with an interface to diamond-anvil and larger-volume cells. Hightemperature high-pressure studies with laser-heated systems and high-pressure lowtemperature studies using a cryostat are among long-term operation projects due to come on line. Detectors include all standard devices: MAR345 image plate and an Oxford diffraction CCD, with a variety of point and photon counting devices. A curved array solidstate detector for texture and in energy-dispersive diffraction experiments is planned. Further designed into the beamline layout are possibilities such as Laue diffraction and simultaneous spectroscopic characterisation of the sample which will enable long-term research versatility. The DCM will have sufficient resolution for particular high-energy inelastic scattering. I15 is based on the EPICS control protocol similar to APS. The implementation adds overhead to operational developments, but will provide a highly flexible, remotely configurable system in the long-term. A full user interface based on PYTHON/JAVA applications will give a look and feel similar across all Diamond beamlines. This software development is also part of the Operation development phase, as are completion of a total of three in-line experimental stations. Currently I15 is accepting user applications while continuing commissioning beamline components. Friday • Session X: Facilities for High Pressure Studies at RAL 41 High-pressure facilities at ISIS Matt Tucker, Bill Marshall and Duncan Francis ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, OX11 0QX, UK Neutron powder diffraction has long been known to be a powerful tool for investigating the structure of condensed matter. This is particularly true when the system of interest contains either low-Z elements, atoms with similar x-ray scattering powers or atomic species possessing unpaired electrons. The penetrating power of neutrons also makes them an ideal choice for high pressure studies. Since the official inauguration of the facility in October 1985, ISIS has been the world’s leading pulsed neutron and muon source and has remained at the forefront in the fields of time-of-flight neutron instrumentation, sample environment and accelerator developments. As with any other neutron or x-ray central facility, ISIS possesses a range of high-pressure sample environment (SE) to permit access to as wide a range of pressure and temperature as the current state of technology permits. I will talk specifically about the PEARL/HiPr instrument and its use for neutron powder diffraction at high pressure. Designed, constructed and commissioned in 1995-96 this highflux, medium-resolution diffractometer has been specifically designed for Paris-Edinburgh cell studies. I will discuss the capabilities and the developments that have taken place over the past 10 years which have made this world-leading facility the focal point of the ISIS high-pressure neutron diffraction program. Finally I will briefly discuss some possible future developments for high pressure studies at ISIS. Friday • Session XI: Future Perspectives and Dynamic Prospects 42 New opportunities in high-pressure research: Small science at big facilities Ho-kwang (David) Mao Carnegie Institution of Washington, USA Recent breakthroughs in high-pressure (HP) research are being spearheaded by small groups or individuals conducting research at large regional users facilities. A plethora of x-ray techniques using synchrotron radiation (SR) facilities has been developed. They include HP x-ray emission spectroscopy which analyzes the lineshape of the x-ray fluorescence spectra to probe the filled electronic states of the HP samples, HP x-ray absorption spectroscopy which analyzes the pre-, near, or extended K- or L-absorption edge spectra to delineate pressure-induced electronic, magnetic, and structural changes, HP x-ray inelastic near-edge spectroscopy which opens a new field of HP chemical bonding studies of light elements, HP electronic inelastic x-ray scattering spectroscopy which accesses to high energy electronic phenomena, including band structure, Fermi surface, excitons, and plasmons, HP resonant inelastic x-ray scattering spectroscopy which probes magnetic spin-resolved electronic structures as well as shallow core excitations and multiplet structures, HP nuclear resonant xray spectroscopy which reveals phonon densities of state and time-resolved Mössbauer information, HP phonon x-ray inelastic spectroscopy which determines phonon dispersive dynamics at meV resolution. Meanwhile, the conventional HP x-ray diffraction continues to be the workhorse for structural and equation-of-state determination of single-crystal, polycrystalline and amorphous materials, HP radial x-ray diffraction yields comprehensive elastic and rheological information, and HP micro-nano x-ray diffraction reaches submicron single crystals. These tools, together with hydrostatic or uniaxial media, laser heating, and cryogenic cooling, are unleashing the power of HP-SR experimentation. The prospective of HP neutron science is equally impressive. With radically improved neutron optics, detectors, source intensity, and HP vessels, we may expect detailed studies of crystal structures, vibrational dynamics, and magnetic ordering of hydrogen, light elements, strongly-correlated electronic systems, and amorphous materials beyond 100 GPa at variable temperatures. In the near future, other major facilities such as the high-energy xray free electron laser, large diamond technology center, and integrated facilities of synchrotron, neutron, nano-fabrication, and electron microscope will also lead to further advances in the multidisciplinary HP science. Friday • Session XI: Future Perspectives and Dynamic Prospects 43 Dynamic exploration of the phase diagram N. C. Holmes Lawrence Livermore National Laboratory With the recent development of graded-density impactors, we can now use gas-gun launchers to explore previously inaccessible regions of the high-pressure phase diagram. While gas-gun experiments have been invaluable for determination of pressure and density, the measurement of temperature and determination of the phase are very challenging, and so far, elusive, particularly compared to static compression experiments. So how do we put dynamic data on the same phase diagram as we make for static compression? We are developing the use of optical methods like absorption and ellipsometry to meet this challenge. While these methods might be viewed as just a way to get the emissivity (required for optical pyrometry), the optical absorption spectrum is a way to directly investigate the electronic band structure. In many metals, the absorption spectrum is characteristic of the crystalline structure. The advantages of this are two-fold: it works well in our geometry with large samples, and it’s easily time resolved. What’s missing is static data that correlates structure with the absorption spectrum at high P and T. The availability of those data will be a new and challenging test for theory. This work was performed under the auspices of the U.S. DOE by LLNL under contract no.W-7405-Eng-48. Poster Abstracts Posters • P1 46 Total energy calculation of high pressure phosphorus: The origin of incommensurate modulations in P-IV G. J. Ackland, M. Marqués, and M. I. McMahon School of Physics and Centre for Science at Extreme Conditions, The University of Edinburgh, Mayfield Road, Edinburgh, EH9 3JZ, UK We present results from experimental and theoretical studies of high pressure polymorphs of phosphorus in the simple cubic, simple hexagonal and, in particular, in the incommensurate modulated P-IV phase. Total energy calculations have been performed within the density functional theory under the generalized gradient approximation using a plane-wave pseudopotential scheme. The distorted structure is approximated by rational approximants corresponding to q=1/2, q=1/4 , q=1/8 , q=2/7 , q=5/7. Phonon frequencies are calculated using density-functional perturbation theory. Both single-crystal X-ray data and ab initio pseudopotential data confirm the recently proposed structure of Ishikawa et al. for the P-IV phase [1]. Here, we show the evolution of structural parameters and modulation amplitudes with pressure. By the evaluation of the density of electronic states for simple cubic, simple hexagonal and modulated phosphorus, we show that the incommensurate instability arises from the opening of a pseudogap at the Fermi level, due to Fermi surface Brillouin zone interactions at intermediate pressures. In addition, to a deeper understanding of the origin of the incommensurate transition, the phonon dispersion curves for simple cubic and simple hexagonal phases of phosphorus will be analyzed in order to detect phonon instabilities. [1] T. Ishikawa et al., Phys. Rev. Lett. 96, 95502 (2006). Posters • P2 47 Crystal-to-crystal phase transition and subsequent amorphisation of NaSi under high pressure O.I. Barkalov, R. Quesada Cabrera, A. Salamat, P. Hutchins*, P.F. McMillan University College of London, Department of Chemistry,Christopher Ingold Laboratories, 20 Gordon Street, London WC1H OAJ, UK *also at Birkbeck University of London, Malet Street, Bloomsbury London WC1E 7HX The Zintl phase of sodium silicide NaSi was for the first time studied by means of X-rays diffraction and Raman spectroscopy under high pressures up to 32 GPa in a diamond anvil cell (see Figure 1). The low pressure monoclinic structure of NaSi compound transformed to one with a higher symmetry in the 4 to 9 GPa pressure interval. This new high pressure phase persisted up to about 20 GPa where solid state amorphisation of the material occurred. Amorphisation process manifested itself by disappearance of narrow crystalline diffraction peaks and forming of a broad halo characteristic for amorphous materials. At somewhat higher pressures, 23–30 GPa a total vanish of the Raman signal from the sample was observed thus also indicative of the sample disordering. This transformation was found to be irreversible upon releasing pressure to the normal one. Figure 1. Series of X-rays diffraction patterns of NaSi obtained upon increasing pressure. Posters • P3 48 Determination of the II’ and IV’ high pressure phases of CuGeO3 Lauren A. Borkowski , Barbara Lavina and Przemyslaw Dera 1 1,2 1,2 2 High Pressure Science and Engineering Center, University of Nevada Las Vegas, Las Vegas, NV 89154-4002, USA 2 Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA Copper metagermanate (CuGeO3) is considered to be the first known inorganic material to display a spin-Peierls transition, and is a model spin-ladder system [1]. For these reasons the response of this material to varying thermodynamic conditions, especially changes in pressure, is of great interest. It is known that CuGeO3 exhibits two different sequences of phase transformations, depending on the hydrostaticity of the pressure medium [2]. Under hydrostatic conditions the material transforms first to a monoclinic phase (II) at 7 GPa [3], then to an orthorhombic phase (II’) at 14 GPa, and finally to a tetragonal phase at 22 GPa (VI) [4], all of which are unquenchable. Under quasi-hydrostatic conditions the material undergoes a completely different set of transformations, starting at 7 GPa with phase III which is quenchable [5], with orthorhombic structure, then proceeds to phase IV at 8 GPa, phase IV’ at 12.5 GPa and finally to phase V at 18 GPa [6]. Previous studies have provided us with the crystal structures of the low-pressure phases (I, II, III, IV) as well as an estimation of the cell dimensions and space groups of the remaining phases although to date, the structures of phases II’, IV’, V, and VI remain elusive. Using a combination of monochromatic (mSXD) and energy-dispersive (EDX SXD) single crystal x-ray diffraction we have been able to obtain new information regarding the crystal structures of phases II’ and IV’. The data were collected at the Advanced Photon Source at Argonne National Laboratory at sectors 13 (GSECARS) and 16 (HPCAT). Both techniques are being developed by our group for the purpose of determining structures of high-pressure non-quenchable phases using micro-single-crystals and are able to provide high-quality cell dimensions, as well as a list of structure factor amplitudes, which can be used for structure determination and refinement. [1] M. Hase, I. Terasaki, K. Uchinokura, Phys. Rev. Lett. 70, 3651 (1993). [2] A. Jayaraman, S.K. Sharma, S.Y. Wang, S.-W. Cheong, Curr. Sci. 71, 306 (1996). [3] A. Yoshiasa, G. Yagyu, T. Ito, T. Yamanaka, T. Nagai, Z. Anrg. Allg. Chem. 626, 36 (2000). [4] L. C. Ming, T. Eto, K. Takeda, Y. Kobayashi, E. Suzuki, S. Endo, S.K. Sharma, A. Jayaraman, T. Kitegawa, J. Phys.: Condens. Matter 14, 10475 (2002). [5] P. Dera, A. Jayaraman, C.T. Prewitt, S.A. Gramsch, Phys. Rev. B. 65, 1 (2002). [6] L. C. Ming, S.K. Sharma, A.J. Jayaraman Y.Kobayashi, E.Suzuki, S.Endo, V. Prakapenka, D. Yang, Spectrochim. Acta A – Mol. Biomol. Spectrosc. 61, 2418 (2005). Posters • P4 49 Pressure-Induced Intermetallic Valence Transition in BiNiO3 Sandra Carlsson , Masaki Azuma , Jennifer Rodgers , Mathew G. Tucker , Masahiko 1 1† 1 1 Tsujimoto , Shintaro Ishiwata , Seiji Isoda , Yuichi Shimakawa1, Mikio Takano 2 and J. Paul Attfield 1 1 2 2 3 Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, Mayfield Road, Edinburgh, EH9 3JZ, United Kingdom 2 Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan 3 † ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom Present Address: Department of Applied Physics, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan Charge ordering in oxides, as observed at the Verwey transition of Fe3O4, drives many important phenomena, e.g. ferroelectricity in LuFe2O4. The melting of charge order often leads to exotic conducting phenomena near the insulator to metal boundary, such as colossal magnetoresistances in manganites (e.g. La0.5Ca0.5MnO3) and superconductivity in K4+ 3+ 5+ and Pb-doped BaBiO3. Disproportionation of Bi into Bi and Bi occurs at the B-sites of 3+ 5+ BaBiO3 (BaBi 0.5Bi 0.5O3), and when suppressed by doping of K for Ba or Pb for Bi, leads to superconductivity. Similar disproportionations of high transition metal valence states are 3+ 5+ 2+ 4+ also known in CaFeO3 (CaFe 0.5Fe 0.5O3) and RNiO3 (RNi 0.5Ni 0.5O3, for R = Y, Pr-Lu), although the observed charge separations are smaller than expected from the ideal formulae shown. The valence state change of BiNiO3 perovskite under pressure has been investigated by a powder neutron diffraction study. At ambient pressure, BiNiO3 has the unusual charge 3+ 5+ 2+ 3+ 5+ distribution Bi 0.5Bi 0.5Ni O3 with ordering of Bi and Bi charges on the A sites of a highly distorted perovskite structure. High pressure neutron diffraction measurements show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous 3+ 3+ charge transfer from Ni to Bi, so that the high pressure phase is metallic Bi Ni O3. This unprecedented charge transfer between A and B site cations coupled to electronic instabilities at both sites leads to a remarkable variety of ground states. The magnetic order in BiNiO3 has also been studied by low temperature powder neutron diffraction. At 5 K, the 2+ spin structure is G-type antiferromagnetic with Ni moments of 1.6(0.3) μB. B Posters • P5 50 Core ionization in compressed alkali and alkali-earth metals Valentina F. Degtyareva Institute of Solid State Physics, Russian Academy of Science, Chernogolovka, Russia degtyar@issp.ac.ru Under compression, simple s-bonded alkali and alkali-earth metals pass through the sequence of phases characterized by lowering in symmetry, coordination number and packing density [1]. Structural transformations in these metals are controlled by the combined effects of electrostatic (Madelung) and electronic (band-structure) contributions to the crystal energy. The latter term increases with pressure yielding low-symmetry complex structures, such as Li-cI16, Rb-oC52 and Cs-oC84. Stability of these structures can be supported by a Hume-Rothery argument when new diffraction planes appear close to the Fermi level [2]. Upon compression up to ~0.4 of initial volume, Cs and Rb form a very open structure tI4 with coordination number 4+4 and packing density ~0.56. The transition to Cs-tI4 is accompanied by an approximately 12% reduction in the atomic radius compared with Csfcc. Considering the Brillouin zone configuration with respect to the Fermi sphere one can conclude that the Hume-Rothery mechanism is effective if the number of valence electrons increases up to ~4 implying the hybridization of the valence band and outer core electrons [2]. In the tI4 structure the loss in the electrostatic energy compared with fcc should be compensated for by the gain in electronic energy that can occur by increase in the number of valence electrons due to the core overlap. The tI4 and oC16 structures in heavy alkalis Rb and Cs are similar to those in polyvalent group IV elements (Si, Ge and Sn) implying the similarity in the valence electron configurations in these two groups metals and supporting an assumption of core ionization in alkalis at much lower pressures than predicted by theory [3]. [1] M. I. McMahon, R. J. Nelmes, Chem. Soc. Rev. 35, 943, (2006). [2] V. F. Degtyareva, Phys. Usp. 49, 369, 2006; I. S. Smirnova and V. F. Degtyareva, BRIZ – a program for the FS-BZ visualization, Institute of Solid State Physics, Russian Academy of Sciences, 2006. [3] M. Ross, A. K. McMahan, Phys. Rev. B 26, 4088, (1982). Posters • P6 51 Structures and transitions in praseodymium at high pressure S. R. Evans, M. I. McMahon, I. Loa, O. Degtyareva, L. F. Lundegaard SUPA, School of Physics and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, UK. The trivalent lanthanide elements exhibit a range of different close-packed structures as a function of increasing 4f occupancy (hcp → Sm-type → dhcp → fcc) [1]. The same series of structures is also accessible in individual lanthanides by the application of pressure. Two further phases can also be accessed on compression. The first, the distorted fcc phase (d-fcc), has a structure that is closely related to the fcc structure, while the second phase, with the alpha-Uranium type, open-packed structure, arises from the delocalisation of the 4f electrons and marks the end of the sequence of close-packed structures. Despite numerous X-ray diffraction studies dating back over 20 years, the structure of the d-fcc phase remains ambiguous. In this poster we present details of our own structural studies of d-fcc Pr made using powder diffraction methods at the SRS and ESRF synchrotrons. In Pr, the d-fcc phase, previously reported to be stable between 9 and ~20 GPa, is found to comprise two different structures. Between 9 and 14 GPa, we find the structure to be rhombohedral [2], and can rule out previous reports of a face-centred monoclinic structure. At 14 GPa, we find a structural transition to a second phase, the structure of which does not appear to agree with that reported recently [3]. Further studies reveal that this second phase also exists in Nd, suggesting that there may be a new high-pressure phase in the general lanthanide phase-transition sequence. [1] W. A. Grosshans and W. B. Holzapfel, Phys. Rev. B 45, 5171 (1992). [2] N. Hamaya, Y. Sakamoto, H. Fujihisa, Y. Fujii, K. Takemura, T. Kikegawa, O. Shimomura, J. Phys. Cond. Matter 5, L369 (1993). [3] V. P. Dmitriev, A. Yu. Kuznetsov, O. Bandilet, P. Bouvier, L. Dubrovinsky, D. Machon and H. P. Weber, Phys. Rev. B 70, 014104 (2004). Posters • P7 52 Single-crystal structure analysis at high pressures of up to 50 GPa A. Friedrich Institut für Geowissenschaften, Abt. Kristallographie, J.W. Goethe-Universität Frankfurt, Frankfurt am Main, Germany friedrich@kristall.uni-frankfurt.de Effective techniques for conducting high-pressure single-crystal X-ray diffraction experiments were developed in the 1970s [1]. Studies up to about 10 GPa are now established using the diamond-anvil cell technique. Due to the experimental difficulties only few full crystal-structure analyses at quasi-hydrostatic conditions were published above 10 GPa with a maximum pressure of about 33 GPa, e.g., [2]. This is insufficient for a very large number of problems, where interesting effects are expected to occur at pressures of ~50 GPa. Recently, a new design of diamond-anvil cell was developed for single-crystal X-ray diffraction, which exhibits the advantages of (1) a large opening angle of 80-90°, (2) avoiding commonly used beryllium or diamond backing plates by the use of small, flat conical diamonds and tightly fitting tungsten carbide seats, and (3) high precision and stability at pressures of up to 50 GPa [3]. With this cell we have pressurized single-crystal samples in compressed helium as pressure-transmitting medium up to 50 GPa. In situ single-crystal synchrotron X-ray diffraction was then performed on a HUBER four-circle diffractometer at HASYLAB (beamline D3), Hamburg, Germany at a wavelength of 0.4 – 0.45 Å. Except for hydrogen, helium is the only pressure-medium that maintains sufficient quasi-hydrostatic conditions for single-crystal experiments at very high pressures. This was proven by the sharpness of the diffraction profiles at even 50 GPa. The results of structure refinements and structure solution at pressures between 15 and 50 GPa will be shown on two case studies: (1) In order to obtain information on the strength and symmetrization of intermediate hydrogen bonds with pressure, diaspore, AlO(OH), was investigated and found to retain its structure up to 50 GPa at room temperature [4]. Conclusions are drawn from the O···O donor-acceptor distance on the strength and symmetrization of the hydrogen bond. (2) The pressure effect on electronic distortions caused by lone pair electrons is commonly proposed to induce a phase transition if the pressure is high enough. We observed a phase transition of Bi2Ga4O9 to a new high-pressure phase between 15 and 30 GPa and solved the complex crystal structure at 30 GPa. It is shown that parameter-free density functional theory based model calculations can be effectively used in order to complement the experimental investigations. Specifically, they can provide detailed electron density maps which cannot be obtained experimentally at high pressure. Financial support from the DFG, Germany, within projects SPP-1236 (Grant WI 1232/25-1) and SPP-1136 (Grant WI 1232/17-2) and from HASYLAB is gratefully acknowledged. This research is funded by the European Science Foundation (ESF) under the EUROCORES Programme EuroMinScI through contract No. ERAS-CT-2003-980409 of the European Commission, DG Research, FP6. [1] [2] [3] [4] R. M. Hazen, L. W. Finger, Comparative crystal chemistry. John Wiley, Chichester, UK (1982). L. Zhang, H. Ahsbahs, A. Kutoglu, Phys. Chem. Minerals 25, 301 (1998). R. Boehler, Rev. Sci. Instrum. 77, 115103 (2006). A. Friedrich, E. Haussühl, R. Boehler, W. Morgenroth, E. A. Juarez-Arellano, B. Winkler, Am. Mineral. (in press, 2007) Posters • P8 53 High pressure studies of Y2O3 nanoparticles Qinfen Gu , Guenter Krauss , Fabian Gramm , Walter Steurer 1 2 1 1 2 1 Lab of Crystallography, ETH Zurich, Switzerland qinfen.gu@mat.ethz.ch Lab of Solid State Physics , ETH Zurich, Switzerland In the last decades, there is a tremendous interest in investigating behaviors of nanocrystals due to their novel properties may differ from bulk materials [1]. The group of rare earth sesquioxides is of special interest due to their technological applications. These materials crystallize with three main structure types: cubic (Mn2O3-type, C), monoclinic (Sm2O3-type, B) and rhombohedral (La2O3-type, A). Their stability at ambient conditions can be understood on the basis of cation and anion size ratios [2]. We studied commercially available Y2O3 nanoparticles (20 nm) at high pressures up to about 30 GPa using powder diffraction with synchrotron radiation and a diamond anvil cell. High-resolution electron microscopy (HRTEM) confirmed the presence of single domain nanoparticles. n-Y2O3 transforms from the C-type to the B-type structure above 19.4 GPa. The transformation is completed at 26.5 GPa. The bulk modulus has been found to significantly decrease from 201(8) GPa for the bulk material to 148(2) GPa for the nanocrystals. At the same time the transition pressure increases from 12 GPa [3,4] to 19.38 GPa. The B-type to A-type phase transition observed in the bulk material [3] was not found in the n-Y2O3. Ab-initio calculations have been performed for the bulk Y2O3 which are in good agreement with the experiments. They also showed a very close energy difference of B-type and A-type structures at high pressures. [1] [2] [3] [4] A. San-Miguel, Chem. Soc. Rev. 35, 876, (2006). V. M. Goldschmidt, F. Ulrich, and T. Barth, Mat. Natur. K1, 5, (1925). E. Husson, C. Proust, P. Gillet, and J. P. Itie, Mater. Res. Bull. 34, 2085, (1999). T. Atou, K. Kusaba, K. Fukuoka, M. Kikuchi, Y. Syono, J. Solid State Chem. 89, 378, (1990). Posters • P9 54 Non-Crystalline Diffraction on the HiPr Diffractometer at ISIS: Accurate Structure Factor Determination at High Pressure. M. Guthrie , C. L. Bull , M. C.Wilding , M. G. Tucker 1 1 1 2 3 SUPA School of Physics and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh, EH9 3JZ, UK 2 3 University of Wales, Aberystwyth, Ceredigion SY23 3BZ, UK ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OXON, OX11 0QX, UK Recently, there has been increasing interest in the structure of the liquid and glassy state at high pressure. Maxima in the melting temperature and corresponding negative melt slopes have now been reported in many systems and may be related to liquid-liquid phase transitions [1]. A negative dP/dT slope implies that both density and entropy increase simultaneously with increasing pressure with the implication that the local bonding arrangements in the liquid may be quite distinct from the solid state. As such, the accurate characterisation of the structure of these distinct phases is important because it provides fundamental information on the true inter-molecular/atomic potentials that may well be distorted in the crystalline state. Neutron diffraction offers several advantages in such structural investigations and, in many cases, complements the data available from synchrotron sources. However, until recently, neutron diffraction has been limited to very low pressures due to the challenging nature of the experiments. The HiPr diffractometer at ISIS has been used for studies amorphous ice since 2001 [2] and developments of a heating set-up [3] have opened the way for a recent study of liquid water up to 6.5 GPa [4]. While this work was ground breaking, further developments were essential to extend the experimental capabilities of this beam line. For this reason, the last 3 years have seen a concerted effort to both increase the maximum experimental pressure and, in particular, achieve quantitative in situ structure factor determination for amorphous phases. To date, we have investigated the structure of MgO-SiO2 glasses in addition to pure silica. Here, we will present both the details of the methodology and some of our S(Q)’s measured to pressures exceeding 20 GPa. [1] see (for example): Tsuji et al., J. Non-Crys. Sol. 117/118, 27 (1990); Brazhkin et al., High Press Res. 6, 363 (1992); Poole et al., Science 275, 322 (1997); Katayama et al., Nature 403 170 (2000); Gregoryanz et al., Phys. Rev. Lett. 94 185502 (2005). [2] S. Klotz et al., Phys. Rev. Lett. 89 285502 (2002). [3] LeGodec et al., High Press. Res. 24 205 (2004). [4] T. Strässle et al., Phys. Rev. Lett. 96 067801 (2006). Posters • P10 55 Pressure-induced change of the chemical short-range order in liquid compounds T. Hattori and K. Tsuji 1 1 2 SPring-8, Japan Atomic Energy Agency, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan 2 Keio University, 3-14-1 Hiyoshi, Kohoku-ku Yokohama 223-8522, Japan To reveal the effect of the covalent/ionic chemical bonding character on the pressureinduced structural changes, we have investigated the structures of various tetrahedrally bonded materials, such as liquid group 14 elements, III-V, II-VI and I-VII compounds, under high pressure [1–4]. The results have shown that these liquids show various highpressure behaviors (local structures and the sharpness of structural changes), depending on the covalent/ionic character. However, these results are based on the average structure, which does not differentiate the chemical component around each atom. To observe partial structures is inevitable to understand the nature of the various structural changes in liquid compounds. For this purpose, we have developed the method to determine the partial structure in liquid compounds at high pressures using an anomalous x-ray scattering method (AXS) and applied it to liquid AgI. The experiment was performed at a JAEA undulator beamline BL22XU in SPring-8. The high pressure and high temperature condition was generated with a multi-anvil highpressure apparatus, SMAP180. The data was collected by an angular dispersive x-ray diffraction method using a solid state detector, which differentiates elastic scattering intensity from the fluorescent x-ray intensity. The incident x-ray energy was tuned into the energies below 300 and 20 eV from the absorption edge of two constituents. The obtained partial structural functions are in good agreement with the results of ab-initio MD calculation [5], which supports the validity of the AXS method to investigate the chemical short-range order in the liquid compounds. [1] [2] [3] [4] [5] T. Hattori et al., PRB 68, 224106 (2003). T. Hattori et al., J. Phys.: Condens. Matter 16, S997 (2004). T. Hattori et al., PRB 72, 064205 (2005). T. Hattori et al., PRB 73, 054203 (2006). F. Shimojo, (private communication). Posters • P11 56 High-pressure study of iron-bearing materials by energy-domain synchrotron radiation Mössbauer spectroscopy Naohisa Hirao , Takaya Mitsui , Yasuo Ohishi , Makoto Seto 1 1 2,4 1 2,3,4 Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan 2 3 Japan Atomic Energy Agency, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-0494, Japan 4 CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 590-0494, Japan In geophysics and mineral physics, much attention has been focused on the behavior of iron in deep Earth materials under high-pressure conditions because of significant influence on large-scale global phenomena in the deep Earth ranging from the differentiation of the early Earth, the subduction and upwelling in the mantle, and the formation of the Earth’s magnetic field. The different electronic configurations of iron in the mineral, such as valence and spin state, could result in potentially different elastic and transport properties of the mineral. However, limited experimental data are available on the high-pressure behavior of iron valence and spin state in deep Earth materials. Mössbauer spectroscopy is one of powerful methods to study the electronic and magnetic structures of materials, and has been used extensively in high-pressure mineralogy in laboratory studies with a radioisotope source. Unfortunately, high-pressure studies in the conventional Mössbauer technique suffer from limited intensity of the radioisotope source. Recent novel advances in X-ray optics and intense X-ray source of a third-generation SR facility allow us to realize an energy-domain SR Mössbauer spectroscopy in conjunction with a diamond-anvil cell (DAC) technique to multimegabar pressure [1,2], where such measurements have been not realized in the conventional Mössbauer spectroscopy using a radioisotope source. We have performed in situ high-pressure experiments on deep Earth materials with a combination of DAC and new energy-domain SR Mössbauer techniques, in order to study the electronic and magnetic states of iron and its environment. In this paper, results of in situ highpressure energy-domain SR Mössbauer measurements will be reported. [1] Mitsui et al., Generation and application of ultrahigh monochromatic X-ray using high-quality 57 FeBO3 single crystal, Jpn. J. Appl. Phys. 46, 821(2007). [2] Mitsui et al., Ultrahigh-pressure measurement in the multimegabar range by energy-domain synchrotron radiation 57Fe -Mössbauer spectroscopy using focused X-rays, Jpn. J. Appl. Phys. 46, L382 (2007). Posters • P12 57 Stress rig for neutron scattering measurements of bulk stress in engineering components at cryogenic temperatures Edward Oliver, Beth Evans, Mohammad Chowdhury, Robert Major, Oleg Kirichek and Zoe Bowden ISIS Facility, Rutherford Appleton Laboratory, STFC, Chilton, OX11 0QX, UK The ENGIN-X beam-line is a dedicated engineering science facility at ISIS. It is optimized for the measurement of strain, and thus stress, deep within a crystalline material using the atomic lattice planes as an atomic ‘strain gauge’. Internal and residual stresses in materials have a considerable effect on material properties including fatigue resistance, fracture toughness and strength. The growing interest in properties of materials at low temperatures may be attributed to the dynamic development in cryogenic technology. This presentation will describe a cryogenic stress rig for neutron scattering measurements of bulk stress in engineering components at temperatures from 30 K to 300 K. Posters • P13 58 Effects of Mg and Si ions to the symmetry of dense aluminum oxide hydroxide K. Komatsu , A. Sano , H. Kagi , E. Ohtani , Y. Kudoh and J. Loveday 1 2 1,2 3 2 4 4 1 Centre for Science at Extreme Conditions, The University of Edinburgh, UK 3 Geochemical Laboratory, Graduate School of Science, The University of Tokyo, Japan The Institute for Solid State Physics, The University of Tokyo, Japan Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Japan 4 Investigations of hydrogen bonding of dense hydrous minerals under pressure are crucial to understand the budget and stability of water in the Earth’s interior. δ-AlOOH, a highpressure polymorph of diaspore (α-AlOOH) and boehmite (γ-AlOOH), has been found to be stable to pressures above 30 GPa at 1000~1200°C, and thus it may serve as a water reservoir in the cold subducted slabs, transporting water into the lower mantle [1,2]. Although there are a number of studies for δ-AlOOH, no consensus exists for the space group of this phase. Based on powder X-ray diffraction data (XRD) the crystal structure of δ-AlOOH was first proposed in the space group P21nm without determining the H atom parameters [3]. Kudoh et al. (2004) [4] reported the space group Pnn2 for the structure of a similar phase containing Mg and Si [δ-(Al0.86Mg0.07Si0.07)OOH] using single-crystal XRD data. For this structure model also identified two partly occupied H sites from difference-Fourier maps. Recently, we measured the single crystal XRD data of δ-AlOOH without Mg and Si, indicating that the space group is unequivocally P21nm [5]. Given that both results of the single crystal XRD studies [4, 5] are true, the interest arises because a little amount of Mg and Si ions may control the symmetry of crystal and hydrogen positions. In order to validate the effects of Mg and Si ions, neutron diffraction patterns for δ-(Al1-x-yMgxSiy)OOH were observed. The polycrystalline samples (30-50 mg) of δ-(Al1-x-yMgxSiy)OOH were synthesized at 18 GPa and 950-1000°C using Kawai-type multi anvil apparatus. Synthesized boehmite (γ-AlOOH) and reagent grade MgO and SiO2 were used as starting materials. Neutron diffractions were measured at ambient conditions using V-can as a sample container on D20 in Institut LaueLangevin, France. The neutron diffraction pattern of a pure δ-AlOOH (x = y = 0) sample was well fitted using the previously reported structure [5-6] with the P21nm space group, which has the systematic absences of h + l odd for h0l, h odd for h00 and l odd for 00l. The pattern of a sample with x = y = 0.07 has an additional systematic absences of k + l odd for 0kl, which suggests the Pnn2 space group corresponding with the single crystal XRD study [4]. However, in the difference Fourier-map of δ-AlOOH, the H2 site which was reported by [4] was not observed. A sample with x = y = 0.01 had intensities for the reflections of k + l odd for 0kl, which indicates in the P21nm space group like a pure δ-AlOOH. These results shows that the threshold for the symmetry change from P21nm to Pnn2 would be exist between x = y = 0.01 and 0.07. [1] [2] [3] [4] [5] [6] Sano et al., J. Phys. Chem. Solid. 65, 1547 (2004). Sano et al., American Geophysical Union, Fall Meeting 2005, abstract #MR41A-0914 (2005). Suzuki et al., Phys. Chem. Mineral. 27, 689 (2000). Kudoh et al., Phys. Chem. Mineral. 31, 360 (2004). Komatsu et al., Acta Crystallogr. E62, i216(2006). Vanpeteghem et al., Phys. Chem. Mineral. (in press, 2007). Posters • P14 59 High-pressure powder and single crystal diffraction on Station 9.5HPT (SRS, Daresbury) – a powerful extreme conditions facility using a novel Laue focusing monochromator Alistair R. Lennie, John E. Warren, Mike C. Miller, David Laundy, Mark A. Roberts, and Graham Bushnell-Wye SRS, Daresbury, UK A novel Laue focusing monochromator, developed to provide intense X-radiation for high pressure powder and single crystal diffraction experiments, has been successfully implemented on Station 9.5HPT at the SRS, Daresbury, providing a dedicated high pressure research facility. The beam is deflected horizontally and focused vertically. The horizontally deflected beam creates space for a range of experimental configurations, while the vertical focusing and bandpass increase of the bent crystal provide the intensity of radiation required for the diamond anvil cell experiment. This station has now been successfully used for a wide range of high pressure powder diffraction studies. In-house PINCER software used to control motorised stages on Station 9.5 HPT has been recently enhanced so that data collection from a mar345 image plate detector can be initiated from the PINCER interface. This new software enables rapid implementation of complex automated routines combining sample stage motion and image plate readout. The geometry of the motorized translation and rotation sample stages (x, y, z, ω) allows reproducible sample centring; with the new software, high-pressure single crystal oscillation data can be collected in small angular steps, within total ω rotations of up to ±40° achievable. We have recently taken single crystal diffraction measurements on Station 9.5HPT from potassium tartrate and gillespite at both ambient and at high pressure in Merrill-Bassett diamond anvil cells. We are in the process of developing single crystal data reduction methods for the oscillation data we have collected. Using this facility, single crystal data collection from both small and large high pressure/temperature cells is now feasible, opening up exciting new possibilities for high pressure research at the SRS. Reference: Alistair R. Lennie, David Laundy, Mark A. Roberts and Graham Bushnell-Wye, A novel facility using a Laue focusing monochromator for high-pressure diffraction at the SRS, Daresbury, UK, J. Synchrotron Radiation 14, 433 (2007). Posters • P15 60 X-ray diffraction study of pressure-induced phase transitions in GeTe-Sb2Te3 (GST) system, a material used as phase change optical recording C. Levelut , R. Le Parc , J. Haines , M. Krbal , A. Kolobov , A. Pradel , M. Ribes , P. Fons , 3 4 J. Tominaga , and M. Han 1 1 1 2 2 2 2 2 3 Laboratoire des Colloides, Verres et Nanomatriaux, UMR 5587 CNRS UM2, Université Montpellier II, Place Eugéne Bataillon, 34095 Montpellier Cedex 5, France 2 Institut Charles Gerhardt, UMR 5253 CNRS UM2 - ENSCM, Université Montpellier II, Place Eugéne Bataillon, 34095 Montpellier Cedex 5, France 3 Center for Applied Near-Field Optics Research, National Institute of Advanced Industrial Science and Technology 1-1-1, Higashi, Tsukuba 305-8562, Japan 4 European Synchrotron Radiation Facility, Grenoble France Quasibinary GeTe-Sb2Te3 alloys with defect NaCl-type structure a material of choice for phase change optical recording such as DVD-RAM. This material was found to become amorphous at high pressure by x-ray powder diffraction experiments both in a He pressure medium and at high temperature on ID09A at the ESRF. The powder diffraction pattern was gradually replaced by a broad amorphous feature at pressures of greater than about 14 GPa. The exact transition pressure does not depend on temperature. XAFS measurements have shown that the local structure around Ge atoms in pressureamorphized GST is very similar to that found in laser-amorphized samples and provided evidence for a decrease in the coordination number from six to four at the crystalline to amorphous transformation in recovered samples [1]. The instantaneous pressure experienced by GST in a capped layer of an optical disk during the laser-induced writing process is of the same order at that used in the present study. Pressure thus appears to be an important factor in the formation of the amorphous phase in devices and the present results provide new insight into the mechanism of phase-change optical recording. [1] A. V. Kolobov, J. Haines, A. Pradel, M. Ribes, P. Fons, J. Tominaga, Y.Katayama, T. Hammouda and T.Uruga, Phys. Rev. Lett. 97, 035701 (2006). Posters • P16 61 Structural mechanism of pressure-induced over-hydration in thomsonite: A synchrotron powder diffraction study A. Yu. Likhacheva, Yu. V. Seryotkin, A. Yu. Manakov, S. V. Goryainov, A. I. Ancharov Institute of geology and mineralogy SB RAS, Russia alih@uiggm.nsc.ru Recent structural studies of fibrous zeolite natrolite Na2Al2Si3O10∗2H2O, compressed in water [1,2], excited a large interest to the over-hydration phenomenon, which consists in the framework expansion due to penetration of additional water molecules into the channels under compression in water medium. In this work we have studied the structure behavior of another fibrous zeolite, thomsonite NaCa2Al5Si5O20∗6H2O, in order to elucidate the influence of variations in the intra-channel water-cation stuffing onto the high-pressure behaviour of fibrous zeolites under compression in water. The powder diffraction experiments were performed at 4th beamline of the VEPP-3 storage ring of Synchrotron centre SSRC, Novosibirsk [3], at a fixed wavelength of 0.3675 Å, using a diamond anvil cell and water-rich mixture of ethanol:water (1:3) as pressure-transmitting medium, at 0–3 GPa. Rietveld refinements of the unit cell and atomic parameters were performed using the GSAS set of programs in the 2 range of 3–25º, to Rwp = 0.006, RF2 = 0.15. At 0–2 GPa the compressibility of thomsonite is markedly lower than that reported previously, where a nominally penetrating medium with 6 % H2O was used [4]. This indicates to a pressure-induced hydration (PIH), which results in the transition to highhydrated phase observed at 2 GPa. The structure of high-hydrated thomsonite contains one additional, half-occupied H2O position, entering the coordination of calcium in the split position Ca(2). This produces a scolecite-like coordination of calcium O4(H2O)3. The resulting chemical formula of high-hydrated thomsonite is NaCa2Al5Si5O20∗6.9H2O. The appearance of new H2O position causes a 4.5 % volume expansion through the cooperative rotation of [(Si,Al)2O5] chains leading to the enlargement of the cross-section of the main channels parallel to c axis. The observed deformation mechanism is similar to that found in high-hydrated and superhydrated natrolite [1,2], although, in the structure of thomsonite only one half of the channels provides free space for additional H2O molecules. The latter seems to determine a difficult response of the thomsonite structure to PIH, showing a large hysteresis and slow kinetics of the transition to the HP phase, as well as a less pronounced volume effect (4.5 %) as compared to natrolite (6.8 %). The present data indicate that the over-hydration effect in fibrous zeolites strongly depends on partial water pressure in compressing medium. This work is supported by RFBR grants # 06-05-64542, 07-05-00742, SibD RAS Integration project 43 and RAS Program P-9-3. [1] [2] [3] [4] Lee et al., J. Am. Chem. Soc. 124, 5466 (2002). Seryotkin et al., Eur. J. Mineral. 17, 305(2005). Ancharov et al., Nucl. Instr. Meth. Phys. Res. A, 470, 80 (2001). Lee et al., Phys. Chem. Minerals, 31, 22 (2004). Posters • P17 62 The high pressure structures of methane H. E. Maynard, J. S. Loveday, E. Gregoryanz, L. F. Lundegaard, C. L. Bull, M. Guthrie, R. J. Nelmes SUPA, School of Physics and Centre for Science at Extreme Conditions, University of Edinburgh, Mayfield Road, Edinburgh, EH9 3JZ, UK Methane is the most abundant organic molecule in our universe and as such its highpressure behaviour is crucial to models of the outer planets and their satellites. There has been much discussion on the dissociation behaviour of this simple molecule within the temperature and pressure regimes of these planetary systems [1]. However, at room temperature, the high-pressure phase diagram of this fundamental molecule is currently not well understood and, again, there has been much debate as to the phase relations of the currently known high-pressure forms [2,3]. Methane is a relatively small neutral molecule, and in f.c.c. phase I (15 kbar, 300 K) can be approximated to a sphere as all the molecules are completely rotationally disordered. However, subsequent transitions at approximately 50 kbar and 90 kbar, to phase A and B respectively, result in bigger and more complex unit cells, the structure of which is still not fully understood. We will present structural studies of two of the high-pressure room temperature phases (A and B) obtained using both x-ray single crystal and neutron powder diffraction techniques. We find the unit cell of phase A to be essentially the same as [4]; and we find the unit cell of 3 phase B we find to be significantly larger (at approximately 1800 Å ) than that proposed in [5]. [1] L.R.Benedetti, J.H.Nguyen, W.A.Caldwell, H.Liu, M.Kruger & R.Jeanloz. Dissociation of CH4 at high pressures and temperatures: Diamond formation in giant planet interiors? Science 286, 100 (1999). [2] R.Bini & G.Pratesi. High pressure infrared study of solid methane: Phase diagram up to 30 GPa. Physical Review B 55, 14800 (1997). [3] P.Hebert, A.Polian, P.Loubeyre & R.LeToullec. Optical studies of methane under high pressure. Physical Review B 36, 9196 (1987). [4] I.Nakahata, N.Matsui, Y.Akahama & H.Kawamura. Structural studies of solid methane at high pressures. Chemical Physics Letters 302, 359 (1999). [5] S.Umemoto, T.Yoshii, Y.Akahama & H.Kawamura. X-ray diffraction measurements for solid methane at high pressures. Journal of Physics: Condensed Matter 14, 10675 (2002). Posters • P18 63 High pressure studies of (N2)11He S. Ninet, G. Weck and P. Loubeyre CEA – Département de Physique Théorique et Appliquée, Bruyères le Châtel, France sandra.ninet@cea.fr High pressure studies of simple elements (H2, He, N2, Ne …) mixtures have demonstrated the existence of a novel class of solid called Van der Waals solids. For example, experimental studies of the N2/He binary diagram[1] have revealed the existence of the stoechiometric compound He(N2)11[2]. At ambient temperature, this solid is stable up to 9 GPa in a large domain of concentration: the binary phase diagram is summarized in Ref. [3]. By X-ray diffraction [2], an hexagonal unit cell with 24 particles has been proposed for He(N2)11. Nevertheless, the space group has not been determined and the pressurevolume dependence has been measured in a limited domain of pressure (9–14.5 GPa). Raman measurements performed up to 40 GPa[4] have revealed that a close relationship exist between the structure of He(N2)11 and the ε-phase of nitrogen. No phase transition was reported in this domain of pressure. In this presentation, we will report recent X-ray and Raman experiments performed on single crystals of He(N2)11 under high pressure. Diamond anvil cells have been loaded with an initial gases mixtures (3%N2/97%) and single crystals of He(N2)11 have been grown from the fluid He/compound phase separation at ambient temperature. Under such conditions, small single crystals of solid He(N2)11 embedded in a helium cushion (hydrostatic conditions) have been realised. Doing Raman scattering and X-ray diffraction, the stability of He(N2)11 has been studied. In particulary, the equation of state and the evolution of the phonon modes have been extended in a large domain of pressure. Finally, the determination of the structure of this compound will be investigated. [1] [2] [3] [4] W.L. Vos and J.A. Schouten, Phys. Rev. Lett. 64, 898 (1990); Physica A182, 365 (1992). W.L. Vos, L.W. Finger, R.J. Hemley, J.Z. Zhu, H.K. Mao and J.A. Schouten, Nature 358, 46 (1992). W.L. Vos and J.A. Shouten, Low Temp. Phys. 19, 338 (1993). H. Olijnyk and A.P. Jephcoat, J. Phys .: Condens. Matter 9, 11219 (1997). Posters • P19 64 Structure of solid ammonia up to 24 GPa by powder neutron diffraction S. Ninet1, F. Datchi1, S. Klotz1, G. Hamel1, J. Loveday2 and A.M. Saitta1 1 Institut de Minéralogie et de Physique des Milieux Condensés, Paris, France 2 School of Physics, University of Edinburgh, Edinburgh, UK Solid ammonia is an archetypal H-bonded solid, but has a more complex H-bond topology than water ice. In phase IV, which is the first ordered high-pressure phase stable at 300 K (above ~4 GPa), it was found by powder neutron diffraction [1] that the 3 H-bonds are nonequivalent, by contrast to the low-temperature solid ammonia I. The structure of this phase IV was recently confirmed by single-crystal x-ray diffraction (SCXRD) at 300 K [2] and polarized Raman scattering at low temperature [3]. The stability of phase IV above ~10 GPa has been a long-standing issue, as well as the occurrence of a symmetric H-bonded solid at high pressure. From our SCXRD experiments to 120 GPa, we showed that an isostructural transition takes place at 12 GPa in NH3 and 18 GPa in ND3. The large isotopic shift suggested a displacement of the H(D) atoms in the transition, but the atomic positions could not be determined from these experiments. To obtain the structure of solid ammonia, we have thus performed neutron powder diffraction experiments in a Paris-Edinburgh cell up to 24 GPa at ISIS. Because of the large incoherent scattering cross-section of the H atoms, deuterated samples were used. We will present the results of these experiments and discuss the origin of the phase transition at 18 GPa. These results will also be compared to ab-initio calculations. [1] J. S. Loveday, R. J. Nelmes, W. G. Marshall, J. M. Besson, S. Klotz and G. Hamel, Phys. Rev. Lett. 76, 74 (1996). [2] F. Datchi, S. Ninet, M. Gauthier, A. M. Saitta, B. Canny and F. Decremps, Phys. Rev. B 73, 114111 (2006). [3] S. Ninet, F. Datchi, A. M. Saitta, M. Lazzeri and B. Canny, Phys. Rev. B 74, 104101 (2006) Posters • P20 65 High pressure and high temperature in-situ Brillouin spectroscopy using infrared laser heating system combined with XRD at SPring-8 Yasuo Ohishi , Motohiko Murakami , Yuki Asahara , Naohisa Hirao , Nagayoshi Sata , 4 and Kei Hirose 1 2 1 2 1 1 3 Material Science Division, JASRI/SPring-8, Hyogo 679-5198, Japan 3 Institute for Study of the Earth’s Interior, Okayama University, Tottori 682-0193, Japan IFREE/ JAMSTEC, Kanagawa 237-0061, Japan 4 Department of Earth and Planetary Science, Tokyo Institute of Technology, Meguro, Tokyo 1528551, Japan The accurate sound velocity data of deep earth material at high pressure and high temperature are essentially required to the interpretation of seismic data, which leads to giving us the strong constraints on the mineralogy of deep earth. Here, we describe a new Brillouin scattering measurement system that has been installed on a synchrotron x-ray beamline at BL10XU/SPring-8 for simultaneous measurements of sound velocities and lattice parameters. Combined system of infrared laser (CO2 laser) heated diamond anvil cell and Brillouin scattering measurements system with x-ray diffraction system at synchrotron facility allows us to successfully obtain the high quality sound velocity and density data under high pressure and high temperature condition relevant to that of earth’s deep interior. The Brillouin spectrometer consists of a Fabry-Perot interferometer, a diode laser and optics (horizontal scattering plane). These are placed on the optical bench which is mounted on heavy-duty linear translation stages for vertical and horizontal motions in order to align the x-ray beam with the energy of ~40 keV. This allows us to independently adjust the x-ray beam spot to the sample without any change for the Brillouin setup, and we can obtain accurate sample position with a resolution better than 3 micron. The Brillouin measurements are performed in a symmetric scattering geometry of 50 degree which was calibrated by both MgO single crystal and glass material (BK7). All combined measurement system (Brillouin, X-ray, laser heating and temperature measurements) is conducted in a same horizontal plane. The laser heating system with water-cooled type DAC achieved the quite stable heating above 2 hours duration during Brillouin experiments. The x-ray CCD is used as an area detector for angle-dispersive x-ray diffraction measurement. This facility has been firstly tested in studies on polycrystalline materials and fluid phase at high pressure and high temperature. We present the latest obtained data and discuss the possible application for the earth’s deep interior and further technical development. Posters • P21 66 High-pressure syntheses of new carbonate phases Shigeaki Ono 1 1,2 Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK 2 Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan There is interest in the behaviour of carbonate minerals at high pressures and high temperatures because of their importance to the Earth’s carbon cycle. The mantle provides CO2 to the surface through degassing of the magmatism, whereas carbonate minerals in sediments and altered oceanic crust can be recycled into the mantle through subduction. Therefore, we have investigated the pressure-induced phase transition of carbonate minerals in several compositions using a diamond anvil cell combined with X-rays from a synchrotron radiation source. High-pressure X-ray diffraction experiments were performed using a laser-heated diamond anvil cell apparatus. The samples were heated with either a YLF or YAG laser to overcome any potential kinetic effects on the possible phase transitions. The heated samples were probed using an angle-dispersive X-ray diffraction technique at the BL13A synchrotron beam line at the Photon Factory (Japan) or the BL10XU beam line at SPring-8 (Japan). Details of the synchrotron X-ray experiments are described elsewhere [1,2]. Powdered samples (MgCO3, CaCO3, SrCO3, BaCO3, MnCO3, and PbCO3) were used in this study. We could discover many high-pressure phases (~10 phases) in this project. Although the crystal structure of some of new phases has not been identified (e.g., [3,4]), two types of structure were confirmed. One is the post-aragonite structure, which appears in CaCO3, 4+ SrCO3, and BaCO3 [4–6]. This structure has C cations exhibiting a three-fold coordination with the oxygen ions, which is same coordination of other known carbonates. Another is the pyroxene-type structure, which was confirmed in MgCO3 and CaCO3 [7,8]. In the case of 4+ the pyroxene-type structure, the C cations exhibit a four-fold coordination. Four-fold coordinated structures are commonly observed in many silicate minerals under ambient conditions. Our study indicates that the pressure-induced phase transition with coordination change from three to four is likely to occur in many carbonate minerals. [1] [2] [3] [4] [5] [6] [7] [8] Ono et al., J. Appl. Phys. 97, 073523 (2005). Ono et al., J. Phys Condens. Matter 17, 269 (2005). Ono, Mineral Mag (2007, submitted). Ono, Phys. Chem. Minerals 34, 215 (2007). Ono et al., Phys. Chem. Mineral 32, 8(2005). Ono et al., Am. Mineral. 90, 667 (2005). Oganov et al., Earth. Planet. Sci. Lett. 241, 95 (2006). Ono et al., Am. Mineral. (2007, in press). Posters • P22 67 Synchrotron studies of halide perovskites at high pressure S. A. T. Redfern , F. Aguado Menendez , G. Bromiley , J. Walsh , M. Kunz , A. Lennie 1 1 1 1 1 2 3 University of Cambridge, Department of Earth Sciences, Cambridge, CB2 3EQ, UK 2 3 ALS, LBL, 1 Cyclotron Road, Berkeley, CA, USA SRS Daresbury Laboratory, Warrington, Cheshire, UK In view of their technological and geophysical importance, intense activity has developed over the years to determine the P-T phase diagrams in perovskites and related compounds, as well as to understand the origin of such instabilities. This activity has been mainly focused on oxides. Our understanding of the behaviour of halide perovskites is significantly less developed, yet these phases provide a fascinating route into building a comprehensive model of perovskite behaviour, given they are the most accessible 1:2 perovksites and they are significantly more compressible than the oxides. Neighborite, NaMgF3, is something of an exception, since it has been employed as a structural analog of magnesium silicate perovskite in Earth’s lower mantle. Recent results show that NaMgF3 undergoes a phase transition to CaIrO3 post-perovksite structure, and a further post-post-perovskite at pressures of around 30 GPa. The behaviour of other halides is completely uncharted, in this respect, yet they provide the potential for a greater variation in crystal chemical responses. In particular they provide an arena in which to explore the general relationships between perovskite compression mechanisms, phase transitions, solid solution formation and transformations to post-perovskite. I will report recent results from studies of a wide variety of perovskite structures with different symmetries, from cubic to orthorhombic. The different ions constituting these perovskites provide a wide range of tolerance factors, from to 0.876 (KCaCl3) to 1.037 (KMgF3) that provide a route to understanding soft perovskites under wide pressure ranges. In addition, we have explored the differences in the pressure behaviour of some chloride-fluoride pairs (CsCaCl3 and CsCaF3, KMgCl3 and KMgF3) to explore the effect of X cation in the compressibility and structural evolution of these perovskites. Recent technical advances in sample environment have included the development of a rotation Paris-Edinburgh cell, in which shear stresses may be applied to ferroelastic perovskites under high pressure, and thus investigate the nature of anelastic responses in these phases and their relationships to phase transformation microstructures. Posters • P23 68 Dense nitride formation using laser heated diamond cells and multianvil presses: from the unstable to the new G. Serghiou University of Edinburgh, School of Engineering and Electronics, Kings Buildings, Mayfield Road, EH9 3JL UK The crystal chemistry of nitrides has been drastically enriched by using high pressures and temperatures. Novel architectures that have arisen are the cubic spinel structure, the thorium phosphide structure, single bonded polymeric nitrogen, and noble nitrides with single bonded dinitrogen units. Much of the recent activity was perhaps initiated by proposals that novel dense carbon nitrides may be formed at high pressures that could be harder than diamond. Using some of our experiments to 75 GPa and 4000 K on group IV and transition metal nitrides, we present examples of candidate crystalline nitrides which do not form at pressure, ones that retain their ambient modifications and ones that transform to novel architectures at high densities, and present some structural criteria governing their formation. Posters • P24 69 Investigation of gas hydrates in ternary systems H2 - CH4 - H2O, H2 - C3H8 - H2O and H2-cross linked tetrabutilammonium polyacrilateH2O at pressures up to 250 MPa and wide range of H2 concentrations S. S. Skiba, E. G. Larionov, A. Yu. Manakov, B. A. Kolesov Nikolaev Institute of Inorganic Chemistry SB RAS, Akad. Lavrentiev ave., 3, Novosibirsk, 630090, Russian Federation Decomposition temperatures of gas hydrates in ternary systems are investigated by means of differential thermal analysis (DTA) at a pressure up to 250 MPa. Phase diagrams of the systems H2 -CH4 - H2O and H2 –C3H8 - H2O are constructed. X-ray diffraction patterns and Raman spectra of quenched hydrate samples in the systems H2 -CH4 - H2O and H2 –C3H8 - H2O are recorded. T C o Isobar 100 MPa T C l+g o Isobar 100 MPa γ+g+l h1+l+g h1+g h1+h2+g h2+l+g h2+g γ+g+l γ+g Isobaric section of the phase diagram of H2 CH4 - H2O at a pressure of 100 MPa. h1– methane hydrate, l–aqueous solution with gas, g–gaseous phase, h2- hydrogen hydrate. Isobaric section of the phase diagram of H2 C3H8 - H2O at a pressure of 100 MPa. γ-solid solution based on the hydrate of cubic structure II, l– aqueous solution with gas, g– gaseous phase. Cross-linked tetrabutilammonium polyacrilat + H2+H2O 20 18 16 Temperature ( C) 14 12 10 8 6 4 0 Q Cross-linked tetrabutilammonium polyacrilat+H2O 500 1000 1500 2000 2500 Decomposition temperatures of the systems H2-Cross Linked Tetrabutilammonium Polyacrilate-H2O and Cross Linked Tetrabutilammonium Polyacrilate-H2O measured by means of DTA method. o Pressure (MPa) Analysis of the data obtained indicated that: 1. For the system H2 -CH4 - H2O with hydrogen content of the initial gas mixture within the range 0 to 70 molar % and at a pressure of 20 MPa and more, the hydrates formed from this mixture have a sI structure in which all the cavities are occupied with methane molecules, while hydrogen molecules are not included in the composition of the hydrate. 2. For the system H2 -C3H8 - H2O within the entire investigated range of pressure and concentrations of the initial gas mixture, a continuous series of solid solutions based on cubic structure II is characteristic. 3. It was shown that decomposition temperatures of the system H2-Cross Linked Tetrabutilammonium Polyacrilate-H2О at pressures up to 250 MPa are higher than those of the system Cross Linked Tetrabutilammonium Polyacrilate-H2О. Posters • P25 70 The high-pressure crystalline structure and lattice dynamics of the heavy alkaline earth hydrides Jesse S. Smith , Serge Desgreniers , John S. Tse , Dennis D. Klug , and Roxana Flacau 1 2 1 1 2 3 1 Laboratoire de physique des solides denses, University of Ottawa, Canada Department of Physics and Engineering Physics, University of Saskatchewan, Canada 3 Steacie Institute for Molecular Sciences, National Research Council of Canada There has been much recent research interest surrounding metal hydrides in various contexts, including hydrogen storage, fundamental lattice dynamics, and ionic AX2 compounds (A = metal). A recent study showed that magnesium hydride undergoes a series of pressure-induced structural phase transitions; above 17 GPa it adopts the cotunnite structure (Pnma), which remains stable up to at least 57 GPa. In contrast, the heavy alkaline earth hydrides MH2 (M = Ca, Sr, or Ba) adopt the cotunnite structure at ambient conditions, suggesting that a pressure-dependent study of these hydrides may offer timely insight into the structural behavior of MgH2 at pressures approaching 100 GPa. We present highpressure powder x-ray diffraction data recently obtained at the Hard X-ray MicroAnalysis beamline at the Canadian Light Source, together with Raman spectroscopy data and firstprinciples calculations, investigating the stability of the heavy alkaline earth hydrides at high pressure and at 300 K. Each undergoes a similar pressure-induced structural phase transition. The proposed structure for the high-pressure phase is the Ni2In structure (P63/mmc), with the alkaline earth metal and hydrogen atoms in special positions. The phase transition can be characterized by an increase in the coordination number of the alkaline earth metal from 9 to 11. This type of pressure-induced structural progression is consistent with that observed for a number of other ionic AX2 compounds. Posters • P26 71 Pressure-induced volume collapse in silicon clathrates P. Toulemonde , D. Machon , S. Le Floch , F. Morales , M. Núñez-Regueiro 1 and A. San Miguel 1 1,2 1 2 2 2 Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Lyon 1 et CNRS, France 2 Institut Néel, CNRS/Université Joseph Fourier, Grenoble, France. pierre.toulemonde@grenoble.cnrs.fr Silicon clathrates are formed by tetrahedral silicon atoms organized in cubic crystalline structures allowing for strong intercalation in their Si20, Si24 and Si28 constituting nanocages [1]. Among the three types of Si-clathrates, the type-I with composition M8Si46 was particularly studied the last eight years. The choice of the M intercalated element influences greatly its stability under pressure [1–5]. In addition, these compounds show under pressure an intriguing isostructural phase transformation with an important volume collapse [2,3]. To understand such kind of phase transition, different explanations have been proposed [3-8]: disorder caused by the migration of some Si atoms from the host lattice, modifications of the hybridization between host silicon and guest atoms, the instability of the silicon framework or the appearance of nesting at the Brillouin zone. We have performed X-ray diffraction, EXAFS, X-ray inelastic scattering and resistivity experiments under pressure on Si-clathrates, in particular on the type-I Ba8Si46, to clarify the nature of this isostructural phase transition. The results of these different investigations will be presented. [1] A. San Miguel, P. Toulemonde, High Press. Res. 25, 159 (2005) and references therein. [2] A. San Miguel et al., Phys Rev B 65, 054109 (2002). [3] A. San Miguel et al., Europhys. Lett. 69, 556 (2005). [4] T. Kume et al., Phys. Rev. Lett. 90 , 155503 (2003). [5] J. Tse et al., Phys. Rev. Lett. 89 195507 (2002). [6] L. Yang et al., Phys. Rev. B 74, 245209 (2006). [7] T. Iitaka, Phys. Rev. B 75, 012106 (2007). [8] A. San Miguel, Chem. Soc. Reviews 35, 876 (2006). Posters • P27 72 New insight on high pressure experiments: X-ray spectroscopy on the FAME beamline at the ESRF Jean-Louis Hazemann , Denis Testemale , Olivier Proux , Eric Lahéra , Pierre Toulemonde 1 2 1 1 2 2 1 Institut Néel, CNRS, Grenoble, France Lab. de Géophysique Interne et Tectonophysique, UMR CNRS/Univ. J. Fourier, Grenoble, France FAME is the French Absorption spectroscopy beamline in Material and Environmental sciences at the ESRF (France), one of the four French Collaborating Research Group (CRG) beamlines, dedicated to X-ray Absorption Spectroscopy (XAS). The aim of this beamline is to cover a wide variety of common applications of XAS in condensed matter physics, materials science, biophysics, chemistry and mainly in geochemistry and geophysics sciences. We have concentrated our effort on the study of diluted systems, small samples and in situ experimental devices. The stability requirements of such XAS spectra acquisitions and the operational simplicity of the instrument for the users were then the main leading factors in the design of the whole beamline and especially the double-crystal 2 monochromator [1]. The size of the monochromatic beam is 300 × 200µm on the sample (H × V, FWHM). Most of the in situ experiments are performed using high pressure devices. For the study of fluids under supercritical conditions (Tc = 374°C, Pc = 22 MPa for water), a dedicated cell has been developed [2]. Its specificities allow a complete separation between pressure and temperature and the possibility to perform XAS experiments both in the transmission mode (study of a concentrated element) and in the fluorescence mode (diluted element). The limitations of this device are a temperature of 1600°C and a pressure of 0.2 GPa. Another cell is under development for the study of large volume solutions from ambient to 1 GPa. First tests have already been done and the cell will be tested under the beam in 2008. Other apparatus can be installed to reach higher pressure: Paris-Edinburg press and Diamond Anvil cells have been successfully used. High-pressure investigation of the leadfree relaxor ferroelectric has been done from ambient to 15 GPa for (Na0.5Bi0.5)TiO3 at the Bi LIII edge [3] and BaTi0.65Zr0.35O3 at the Zr K-edge. [4] More recently study of the local structure of Zn in Zn1− x Be x Se mixed crystals has been probed from ambient to 20 GPa [5]. The reduction of Selenium by Agrobacterium tumefaciens, which reduces under pressure selenite IV VI 0 (Se ) and selenate (Se ) into elemental selenium (Se ) and dimethyl-selenide has been followed using XANES using a dedicated DAC [6]. The high flux, the size of the focused beam and the stability of the entire optical elements allow now to regularly use high pressure facilities on CRG-FAME. Such experiments are actually mainly in the geochemistry, environmental or material sciences fields. Moreover, these properties allow to conduct high resolution X-ray spectroscopies experiments (RIXS, XES, IXS...). The development of a new spectrometer suitable for high pressure purpose is under progress. Measurements at the O K-edge of water using hard x-ray will be presented. [1] Proux O., Nassif V., Prat A., Ulrich O., Lahera E., Biquard X., Menthonnex J.-J. and Hazemann J.L., Journal of Synchrotron Rad. 13, 59-68 (2006). [2] Testemale D., Argoud R., Geaymond O., Hazemann J.-L., Review of Scientific Instruments 76, 043905 (2005). [3] Kreisel J., Hippert F., Chaabane B., Dkhil B., ESRF Experimental Report HS 2115 (2003). [4] Hippert F., Laulhé C., Kreisel J., Bouvier P., ESRF Experimental Report 30 02 733 (2005). [5] Polian A., Pages O., Itié J.-P., ESRF Experimental Report 30 02 792 (2007). [6] Oger P. M., Daniel I., Picard A., Biochimica et Biophysica Acta 1764, 434–442 (2006). Posters • P28 73 Stepwise structural transitions of β-Sr0.33V2O5 observed under high pressure Hiroaki Ueda , Touru Yamauchi , Kanji Ohwada , Hajime Sagayama , 3 1 Hiroshi Sawa and Yutaka Ueda 1 1 1 2 3 Institute for Solid State Physics, University of Tokyo, Chiba 277-8581, Japan 2 3 Japan Atomic Energy Agency, Hyogo 679-5148, Japan High Energy Accelerator Research Organization, Ibaraki 305-0801, Japan β-vanadium bronze A0.33V2O5 is a series of quasi-one-dimensional conductors, which have mixed-valence states, and most of which exhibit charge order transitions. Compounds with a monovalent ion as A-site (A = Li, Na, Ag) exhibit pressure-induced superconductivities when the charge ordered state are suppressed. On the other hand, no superconductivity is found for those with a divalent ion (A = Ca, Sr), though the charge order phases disappear around 1 GPa. To elucidate the origin of different properties between monovalent and divalent compounds, we have conducted detailed measurements of compounds with divalent ion under pressure. At ambient pressure, β-Sr0.33V2O5 and β-Ca0.33V2O5 have an anomaly in resistivity and susceptibility data at charge ordering temperatures. Below those temperatures, spin gap states are formed. By applying pressure, charge ordering temperatures gradually reduce and then additional anomalies are clearly observed in magnetical measurement, indicating the appearance of new phases [1]. Single crystal x-ray diffraction measurements of β-Sr0.33V2O5 under high pressure were conducted at Photon Factory, which reveals that these anomalies correspond to structural changes. In the structural view point, pressure-temperature phase diagram is divided into four main phases. Furthermore, in the vicinity of the point where these four phases meet, we observed many kinds of commensurate superlattice signals by changing temperature, indicating stepwise structural transitions. These stepwise transitions are systematically explained from a symmetrical view point. We propose that coupling between charge degrees of freedom in one-dimensional chains and lattice softening plays an essential role in this phenomenon. [1] T. Yamauchi, H. Ueda, J.-I. Yamaura, and Y. Ueda, Phys. Rev. B 75, 014437 (2007). Posters • P29 74 Structural studies of fluid oxygen at high pressure and high temperature G. Weck , J. Eggert and P. Loubeyre 1 1 2 1 CEA, Physique de la matière condensee, BP12, 91680 Bruyères le Châtel, France 2 LLNL, 7000 East Ave, Livermore Ca, USA Remarkable structural changes have recently been disclosed at high pressure in simple molecular solids, more particularly in H2 [1], O2 [2, 3], N2 [4] or CO2 [5]. Similarly, the combining effects of density and disorder should also produce a variety of interesting transformations in dense molecular fluids such as polymerization, dissociation or metallization. Fluid O2 is a good candidate for observing interesting structural changes at high pressure. First, metallization has been observed in the solid above 96 GPa [6, 7] and above 120 GPa in the fluid[8]. Moreover, the formation of O8 molecular units in the solid above 12 GPa has recently been demonstrated by single crystal x-ray diffraction [2] and powder X-ray diffraction [3]. A main motivation of the present study is to observe whether or not a similar association of oxygen molecules exists in the dense fluid within the same pressure range. The presentation will be organized as follows. We will first present a new determination of the melting line up to 750 K because it is the boundary limit of the fluid domain, where density induced structural changes in the fluid are expected to be maximized. Then we will present Raman measurements of the vibron O2 mode. These measurements indicate that over the P-T range of this study the intra-molecular bonding of the O2 molecule is hardly changing. Finally we will present the evolution with density of the structure factor of fluid O2 and a comparison with a molecular dynamic simulation performed with an effective pair potential derived from shock wave data. [1] I. Goncharenko and P. Loubeyre, Nature (London) 43, 1206 (2005). [2] L.F. Lundergaard, G. Weck, M.I.McMahon, S. Desgreniers and P.Loubeyre, Nature (London) 443, 201, (2006). [3] H. Fujihisa, Y. Akahama, H. Kawamura, Y. Ohishi, O. Shimomura, H. Yamawaki, M. Sakashita, Y. Gotoh, S. Takeya, and K. Honda, Phys. Rev. Lett 97, 085503 (2006). [4] M. I. Eremets, A.G. Gavriliuk, I.A. Trojan, D. A. Dzivenko, and R. Boehler, Nature Materials 3, 558 (2004). [5] M. Santoro, F. A. Gorelli, R. Bini, G. Ruocco, S. Scandolo and W. A. Crichton, Nature (London) 441, 857 (2006). [6] S. Desgreniers, Y. K. Vohra and A. L. Ruoff, J. Phys. Chem. 94, 1117 (1990). [7] K. Shimizu, K. Suhaura, M. Ikumo, M.I. Eremets, and K. Amaya, Nature (London) 393, 767, (1998). [8] M. Bastea, A. C. Mitchell, and W. J. Nellis, Phys. Rev. Lett. 86, 3108 (2001). Posters • P30 75 Between open and dense: a new modification of Germanium: Ge(hR8) Aron Wosylus and Ulrich Schwarz Max Planck Institute of Chemical Physics of Solids, Dresden, Germany Recently [1] a new modification of Germanium was prepared by chemical oxidation of alkaline metal germanides by ionic liquids. This polymorph [further labelled as Ge(cF136)], with an empty clathrate-II-type structure, comprises a four-bonded, nearly tetrahedrally arranged network, with large voids where originally the metal atoms were placed. The density of this open, porous structure is naturally lower than that of the Ge(cF8) justifies a pressure driven structural phase transition under pressure. We investigated the influence of pressure on Ge(cF136) by means of in-situ X-ray powder diffraction in a diamond anvil cell using the ESRF BL ID09a. The structure started to transform to Ge(tI4) with β-Sn type structure at about 8 GPa. Surprisingly not all diffraction peaks can be indexed on the basis of Ge(cF136) and Ge(tI4)! The analysis reveal that the additional diffraction lines arise from a structure, which is isotypic to Si(hR8) [2]. By fitting the intensities using Rietveld refinements we could confirm the assignment and were able to follow the structure development under pressure. The changes of the atomic volume with respect to pressure are shown in the left figure. It is clearly visible that the volume of the new modification lies between that of Ge(cF136) and Ge(tI4). The crystal structure (figure on the right) consists of a four-bonded network like Ge(cF136), but the angles are more distorted ranging from 90 to 140°. Similar to the atomic volume the bond-length of the germanium atoms are between that of Ge(cF136) and Ge(tI4). [1] A. M. Guloy et al., Nature 443, 320 (2006). [2] J. Crain et al., Phys. Rev. B 50, 13043 (1994). Posters • P31 76 High Pressure X-Ray Diffraction Studies and Compressibility of ThSi and USb2 Compounds S. Yagoubi , R. Caciuffo, F. Wastin, J. Rebizant, T. Lebihan, S. Heathman European Commission, Joint Research Centre-Institute for Transuranium Elements (ITU), Postfach 2340, D-76125 Karlsruhe, Germany 1 Said.Yagoubi@ec.europa.eu 1 The high-pressure X-Ray diffraction behavior of two actinide compounds ThSi and USb2 have been studied using Le-Toullec type diamond anvil cells (DAC) with nitrogen and silicone oil pressure transmitting media respectively. The crystal structure of ThSi has been investigated by X-ray powder diffraction under pressure up to 54 GPa applying synchrotron radiation at the European Synchrotron Radiation Facility in Grenoble (ID30). High quality diffraction patterns [Fig. 1] were collected on a Mar345 image plate with a beam size of 20 µm x 20 µm at fixed wavelength of 0.3738 Å. Data reduction was performed with standard software Fit 2D [1] and 1D powder patterns generated. Le Bail [2] fitting and Rietveld [3] refinement were applied to extract cell dimensions and refine atomic positions as a function of pressure. The bulk modulus and the pressure derivative were calculated, [Fig. 2]. ThSi Birch B0 = 96.4 B´0 = 4.3 Vinet B0 = 95.3 B´0 = 4.6 V/V0 Pressure [Gpa] Figure 1: Rietveld Refinement of ThSi recorded at 41 GPa Figure 2: Reduced volume of ThSi versus pressure in GPa For USb2, the crystal structure has been investigated by X-ray powder diffraction in the pressure range up to 36 GPa applying Molybdenum radiation at the ITU high pressure laboratory. The diamond anvil cell is mounted onto a modified Bruker Smart System equipped with an APEX 1024K detector system and focusing Göbel mirror optics. A phase transformation from the normal tetragonal structure to an orthorhombic structure similar to that was observed in other isotype compounds [4,5] USb2 was observed at 10 GPa, [Fig. 3]. Figure 3: Debye Scherrer rings showing a phase transformation from the tetragonal structure to an orthorhombic structure in USb2 [1] A. P. Hammersley, S. O. Svensson, High Press. Res. 14, 235 (1996). [2] A. Le Bail, H. Duroy, J. L. Fourquet, Mat. Res. Bull. 23, 447 (1988). [3] H. M. Rietveld, J. Appl. Cryst. 2, 65 (1969). [4] U. Benedict, S. Dabos, H. Luo, High Temp. High Press. 22, 523 (1990). [5] L. Gerward, J. Staun, U. Benedict, High Press. Res., 13, 327 (1995). Posters • P32 77 First-principles crystal structure prediction Yansun Yao and John S. Tse Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, S7N 5E2, Canada The objective of this research is determining unknown crystal structures from fundamental physics laws, using the state-of-the-art parallel computation techniques. We have developed a code for crystal structure prediction based on first-principles density functional theory by incorporating features described in several recently proposed evolutionary algorithms [1-4]. The goal is to predict the most stable crystal structure and/or energetically favourable meta-stable crystal structures from the knowledge of only constituent elements at any given pressure or volume condition. Besides the crossover, mutation, and permutation operations introduced before [1-4], we implemented ‘nudged cell’ method [5] into our code to search for the local minima in free energy surface. In order to search for the meta-stable structures, which are considered as the offspring evolved at different evolutionary stages, we distinguish the structures by their space groups and radial distribution functions, and always keep some lowest energy structures from each generation. Taking advantage of evolutionary procedures from selected low energy candidate structures, randomly generated structures evolve gradually into lower energy phases after a few generations. As a test, we have performed structure prediction calculations on elemental silicon from 0 to 80 GPa and successfully recovered all known stable and meta-stable phases within this pressure range. We have also investigated the high-pressure structures of calcium. We predicted a new stable structure and several metastable structures that might explain the diffraction pattern of Ca IV and Ca V in the pressure range from 100 to 160 GPa. [1] [2] [3] [4] [5] D. M. Deaven and K. M. Ho, Phys. Rev. Lett. 75, 288 (1995). N. L. Abraham and M. I. J. Probert, Phys. Rev. B 73, 224104 (2006). A. R. Oganov and C. W. Glass, J. Chem. Phys. 124 (2006) 244704. G. Trimarchi and A. Zunger, Phys. Rev. B 75, 104113 (2007). Y. Le Page and J. R. Rodgers, Comp. Mater. Sci. 37 (2006) 537.