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					SCALING OF THE STRUCTURAL RELAXATION IN FRAGILE AND STRONG GLASSFORMING LIQUIDS
A. Le Grand, C. Dreyfus, C. Bousquet and R.M. Pick
I.M.P.M.C., Université Pierre et Marie Curie-Paris 6 and CNRS-UMR 7590, Paris, France
catherine.dreyfus@impmc.jussieu.fr                                                                                                   Formatted: English (United Kingdom)
A scaling law for the alpha relaxation time, tau, involving the ratio of a density-dependent energy to the thermal
energy, has been found to hold in many fragile glass-forming liquids. This scaling has been recently linked to a local
quantity, nloc(d,T) relating the variation of the alpha relaxation time with density, d, to its variation with
temperature, T. In many fragile liquids, the variation of nloc(d,T) is weak enough to take it as constant over the
experimental temperature and density domain. We show that simulated liquid silica has an opposite behavior; close to
Tg, nloc is negative for moderate densities and exhibits a significant variation with d and T, reaching positive values
for higher temperature and/or densities. Moreover, those variations linearly correlate to a measure of the bonding
properties of the liquid.
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[1] Reference 1 (Journal of Non-Crystalline Solids style should be used)
[2] Reference 2 (Journal of Non-Crystalline Solids style should be used)

EXAMPLE EXTRACTED FROM THE 5IDMRCS BOOK:

NEUTRON SCATTERING STUDY OF THE VIBRATIONS IN VITREOUS SILICA AND GERMANIA: A NEW
PROCEDURE TO TREAT THE INELASTIC NEUTRON SCATTERING DATA
E. Fabiani (1), A. Fontana (2) and U. Buchenau (3)
(1) Institute Laue-Langevin, BP 156, F-38042 Grenoble Cedex 9, France
(2) Dipartimento di Fisica and Istituto Nazionale per la Fisica della Materia, Universita di Trento, 38050 Povo (Trento), Italy
(3) Institut für Festkörperforschung, Forschungszentrum Jülich, Postfach 1913, 52425 Jülich, Germany
buchenau-juelich@t-online.de
We report thermal neutron time-of-flight measurements on vitreous silica and vitreous germania taken over a large
momentum transfer range with the spectrometer IN4 at the High Flux Reactor at the Institut Laue Langevin in Grenoble. The
high quality of the data allows for an evaluation which goes beyond the usual incoherent approximation, extending and
improving early work [1,2]. We extended the incoherent approximation for the determination of the vibrational density of
states of glasses from inelastic neutron or x-ray scattering data to treat the coherent scattering. The inelastic dynamic
structure factor at the boson peak turns out to be well described in terms of a mixture of rotation and translation of practically
undistorted SiO4 or GeO4 tetrahedra. The comparison with the heat capacity data from silica and germania between 1 and 20
K was used to check the vibrational density of states obtained by this way. The good agreement between the calculated and
the experimental data shows the validity of this new procedure.
[1] U. Buchenau, M. Prager, N. Nücker, A. J. Dianoux, N. Ahmad and W. A. Phillips, Phys. Rev. B, 34, 5665, 1986
[2] A. Wischnewski, U. Buchenau, A. J. Dianoux, W. A. Kamitakahara and J. L. Zarestky, Phys. Rev. B, 57, 2663, 1998

				
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