1108 Journal of the Chinese Chemical Society, 2009, 56, 1108-1111
Synthesis and Structure Analysis of Aurivillius Phases
Zulhadjri,a B. Prijamboedi,a A. A. Nugrohob and Ismunandara,*
Inorganic and Physical Chemistry Group, Faculty of Mathematics and Natural Sciences,
Institut Teknologi Bandung, Jl. Ganesa No. 10 Bandung, Indonesia
Magnetic and Photonic Physics Research-Group, Faculty of Mathematics and Natural Sciences,
Institut Teknologi Bandung, Jl. Ganesa No. 10 Bandung, Indonesia
Synthesis Pb1-xBi4+xTi4-xMnxO15 compounds (0 £ x £ 1) were carried out by molten salts method using
eutectic mixture of Na2SO4/K2SO4 salts (1:1 molar ratio) as the flux. The samples were characterized by
X-ray powder diffraction and refined by Le Bail method using Rietica program. The refinement results re-
vealed that the compounds with the composition 0 £ x £ 0.6 formed Aurivillius phase with the space group
A21am while the other composition (x ³ 0.8) showed another phase beside A21am. The ratio b/a of the lat-
tices constants for all the samples are larger than 1 indicating the direction of the orthorhombic along the b
axis of their cells. The lattice parameters and volume of the unit cells decrease as the Mn content increas-
ing from x = 0 to 0.6, for x ³ 0.8 a second phase were observed. The morphologies of Pb1-xBi4+xTi4-xMnxO15
samples were observed by SEM and show plate-like aggregate crystals, typical of layered compounds be-
longing to the Aurivillius phase.
Keywords: Aurivillius phases; Molten-salts; Le Bail method.
INTRODUCTION often lead to inhomogeneous composition, because it is
Recently, the materials showing magnetoelectric done in the high temperatures (>1000 °C), incomplete of
properties have attracted much of interests. Magnetoelec- mixing, and long reaction times (>2-4 days). In addition
tric materials consist of conventional “ferroelectric (d 0) bismuth oxides are relatively volatile and the manganese
cations” and “magnetic (d n) cations” in one phase. This content strongly affect whether we could obtain a single
type of materials considered now as promising materials phase Aurivillius that contain both Ti4+ and Mn 3+ in the
for magnetic sensors, storage media and spintronics de- perovskite block or not.
vices.1-3 Aurivillius phases are ideal candidates for this pur- It has been reported that BiMnO3 with a highly dis-
pose because these phases consists of perovskite blocks torted perovskite could be synthesized using high pressure,
with composition [An-1BnO3n+1]2- wherein they can be built i.e. at 6 GPa.8 Therefore, it can be assumed that Aurivillius
by combination of d 0 and d n in the middle octahedral compounds containing Mn 3+ ion can be synthesized by
sheets.4-6 These blocks are separated by fluorite-like [Bi2O2]2+ high pressure technique or other techniques that give high
layers. homogeneity in their precursor such as molten-salt (flux)
Extensive studies have been conducted on Aurivillius technique. Molten salt (flux) synthesis method has been ap-
phases such Bi4Ti3O 12. mBiMnO 3 (m = 1, 2) system in plied by Digamber et al. 6 and Fuentes et al. 9 to produce
which a ferroelectric (Bi4Ti3O12) is combined with m mol magnetoelectric compounds, Bi5Ti3FeO15 using Na2SO4/
BiMnO3 (ferroelectric, ferromagnetic). There have been K2SO4 and NaCl/KCl as the fluxes, respectively. Molten
several report described the synthesis of these compounds flux could accelerate the reaction kinetics, hence reducing
by solid-state reaction; 7 however the results are still time and temperature of synthesis. These are important
showing presence of impurity and other phases and con- growing variables, which enable Aurivillius phase with
flicting results often becoming controversy. Syntheses of different valence of Ti4+ and Fe3+ in perovskite block to be
Bi4Ti3O12.mBiMnO3 by conventional solid-state reaction obtained. The Aurivillius phases Bi5Ti3FeO 15 formed at
* Corresponding author. Fax: +62-22-250 4154; E-mail: firstname.lastname@example.org
Synthesis and Structure of Pb1-xBi4+xTi4-xMnxO15 J. Chin. Chem. Soc., Vol. 56, No. 6, 2009 1109
flux temperature 850 °C and showed good crystallinity and and the others Aurivillius compounds with n = 4 in Interna-
purity at higher temperature (900 to 1000 °C). tional Crystallography Standard Data (ICSD). There are
The aim of this work is to synthesize Aurivillius several space groups reported for n = 4 of Aurivillius
phases, n = 4 containing magnetic and ferroelectric cations, phases i.e. A21am (ICSD # 51862, Kennedy et al.11), Fmm2
Pb1-xBi4+xTi4-xMnxO15 with composition 0 £ x £ 1 by mol- (ICSD # 154483), and I4/mmm (ICSD # 150929). These
ten-salt method and analyze their crystals structure by Le space groups were tested in the refinements of XRD data
Bail technique using Rietica program. samples by Le Bail method using Rietica program for all
samples with x £ 0.6, and the best fit were obtained using
EXPERIMENTAL A21am space group. The fitting results of refinement X-ray
Stoichiometric quantities of raw materials (TiO 2, diffraction data by Le Bail technique for all of samples are
Mn2O3, Bi2O3, and PbO with high purity, aldrich ³ 99.9%) shown in Fig. 2.
were mixed in agate mortar. The mixtures of raw materials The cell parameters of Pb1-xBi4+xTi4-xMnxO15 refined
were ground with the eutectic mixture of Na2SO4/K2SO4 by Le Bail method are shown in Table 1. From these data
salts (1:1 molar ratio). The molar ratio of oxide compounds the ratio of lattice constants b/a for all samples is larger
to the flux mixture was 1:7, which was excess in flux. The than 1 meanwhile the pattern of lattice constants applied in
reactant mixtures were placed inside an alumina crucible refinement were Bi5Ti3FeO15 which are a = 5.4698(1) Å, b
and heated at temperatures of 750 °C, 850 °C, and 950 °C = 5.4389(1) Å and c = 41.197(1) Å.10 These indicate that
for 20 h. The products were washed several times with hot the direction of the orthorhombic for our products is along
distilled water to remove the alkali metal salts and dried at the b axis of their cell. This ratio for Bi5Ti3MnO15 reported
110 °C for 20 h. The crystals samples were pressed into the by Kumar et al.7 is also upper than 1 with value 1.007.
pellet and then were heated at 1050 °C for 15 h. The forma- The variation of the lattice parameters and volume of
tion of a single phase oxide was confirmed by powder XRD the unit cells of the samples as a function of Mn content is
measurements at room temperature on a PANalytical model shown in Fig. 3. The lattice constants and the volume unit
PW 3373 instrument. X ray powder diffraction patterns cell decrease with the increase of Mn content until x = 0.6
were refined by Le Bail method using Rietica program to mol. It is known that the ionic radii of Pb2+, Bi3+, Ti4+, and
determine their crystals structures. The surface morphol- Mn3+ are 1.45 Å, 1.28 Å, 0.75 Å, and 0.79 Å, respectively.12
ogy of products was characterized by scanning electron Based on these radii, the substituting of Ti4+ by Mn3+ and
microscopy (SEM) using JEOL, JSM-6360LA instrument. Pb2+ by Bi3+ should give decreasing in the lattice constant
RESULTS AND DISCUSSION
In this study, the samples Pb1-xBi4+xTi4-xMnxO15 has
been synthesized by heating mixture of raw materials and
fluxes with several steps of temperature. The heating was
started at 750 °C to prevent melting of bismuth oxides.
When the samples heated at 1050 °C, the products melt and
became harder in the flux. Therefore, the alkali metal salts
were removed after heated at 950 °C. The polycrystals
product without containing Mn cation showed cream color
and changed to black colors as the samples containing Mn
Fig. 1 shows the X-ray diffraction pattern (XRDP) of Fig. 1. Powder X-ray diffraction pattern of
Pb1-xBi4+xTi4-xMnxO15 with compositions 0 £ x £ 1. In gen- Pb 1-x Bi 4+x Ti 4-x Mn x O 15 synthesized by molten
eral, all of the XRDP products are similar, except for x ³ 0.8 salt method, a) x = 0 (PbBi4Ti4O15), b), x = 0.2
(Pb 0.8 Bi 4.2 Ti 3.8 Mn 0.2 O 15 ), c) x = 0.4
(Bi5Ti3MnO15) in which shows splitting in some peaks i.e.
(Pb 0.6 Bi 4.4 Ti 3.6 Mn 0.4 O 15 ), d) x = 0.6
around 2q = 28°, 30°, and 38° and appearance of another (Pb 0.4 Bi 4.6 Ti 3.4 Mn 0.6 O 15 ), e) x = 0.8
peak around 2q = 15°. Similar phenomena were observed (Pb 0.2 Bi 4.8 Ti 3.2 Mn 0.8 O 15 ), and f) x = 1
in the magnetoelectric Aurivillius phases9,10 of Bi5Ti3FeO15 (Bi5Ti3MnO15).
1110 J. Chin. Chem. Soc., Vol. 56, No. 6, 2009 Zulhadjri et al.
Table 1. Cell Parameters of Pb1-xBi4+xTi4-xMnxO15 a)
PbBi4Ti4O15, b) Pb0.8Bi4.2Ti3.8Mn0.2O15, c)
Pb0.6Bi4.4Ti3.6Mn0.4O15, d) Pb0.4Bi4.6Ti3.4Mn0.6O15 refined
with A21am space group
Parameters a b c d
a (Å) 5.4254(5) 5.4184(5) 5.4116(4) 5.4005(6)
b (Å) 5.4448(3) 5.4407(4) 5.4375(4) 5.4375(5)
c (Å) 41.270(3) 41.201(3) 41.195(3) 41.196(4)
V (Å3) 1219.1(2) 1214.6(2) 1212.2(1) 1209.7(2)
b/a 1.004 1.004 1.005 1.007
Z 4 4 4 4
Rp (%) 2.14 2.30 1.740 2.49
Rwp (%) 3.15 3.60 2.35 3.51 Fig. 3. Lattice constants and volume of the unit cell as
c2 4.636 6.763 1.343 1.656 a function of Mn content for
Pb1-xBi4+xTi4-xMnxO15 with 0 £ x £ 0.6.
Fig. 2. Plot Le Bail of X-ray powder diffraction of com- Fig. 4. SEM micrographs of Pb 1-x Bi 4+x Ti 4-x Mn x O 15
pounds a) PbBi4Ti4O15, b) Pb0.8Bi4.2Ti3.8Mn0.2O15, synthesized by molten salt method, a)
c) Pb0.6Bi4.4Ti3.6Mn0.4O15, d) Pb0.4Bi4.6Ti3.4Mn0.6O15. PbBi 4 Ti 4 O 15 , b) Pb 0.8 Bi 4.2 Ti 3.8 Mn 0.2 O 15 , c)
Observed X-ray diffraction intensity (circle), Pb 0.6 Bi 4.4 Ti 3.6 Mn 0.4 O 15 , d)
calculated data (solid line), the difference of Pb0.4Bi4.6Ti3.4Mn0.6O15.
patterns, y obs - y cal (solid line on the bottom
curve) and the small bars show the positions of
allowed Bragg reflections in the space group
The Aurivillius compounds Pb1-xBi4+xTi4-xMnxO15 (0
£ x £ 0.6) which containing magnetic and ferroelectric cat-
and the volume of unit cell as Mn content increasing. The ions were prepared by molten-salt synthesis method using
lattice constants and the volume unit cell of the experiment Na2SO 4/K 2SO 4 mixture as the flux. These compounds
are in agreement with the theoretical calculated according adopt orthorhombic structure with space group A2 1am,
to radii cations on the mol Mn = 0.2 – 0.6. It is difficult to however in the case of x = 0.8 and 1 mol, the products con-
replace completely one mol of Ti4+ by Mn3+ in which both tain impurities. The direction of the orthorhombic for all of
are different valence and symmetry. the samples is along the b axis of their cells.
The morphologies of Pb1-xBi4+xTi4-xMnxO15 samples
were observed by SEM as shown in Fig. 4. It can be seen ACKNOWLEDGMENTS
that the powder products are a plate-like aggregate crystals, The authors acknowledge the financial support from
typical of layered compounds belonging to the Aurivillius ITB Bandung under Program Riset ITB No Kontrak
Synthesis and Structure of Pb1-xBi4+xTi4-xMnxO15 J. Chin. Chem. Soc., Vol. 56, No. 6, 2009 1111
041/K01.7/RL/2008. Zulhadjri thanks to the Ministry of 5. McCabe, E.-E.; Greaves, C. J. Mater. Chem. 2005, 15, 177.
National Education of the Republic of Indonesia for BPPS 6. Digamber, G.-P.; Maggard, P.-A. Mater. Res. Bull, 2006, 41,
7. Kumar, M.-M.; Srinivas, A.; Kumar, G.-S.; Suryanarayana,
S.-V. Solid State Commun. 1997, 104, 12, 741.
Received February 12, 2009. 8. Chi, Z.-H.; Xiao, C.-J.; Feng, S.-M.; Li, F.-Y.; Jin, C.-Q. J.
Appl. Phys. 2005, 98, 103519.
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