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X-ray room temperature structure from single crystal data, powder diffraction measurements and optical studies of the Aurivillius phase Bi5(Ti3Fe)O15

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Published in Ferroelectrics. 1992, vol. 129, no. 1-4, p. 101-112
Abstract The room temp. structure of the ferroelastic and presumably ferroelec. Aurivillus type compd. Bi5(Ti3Fe)O15 (dc = 8.065, Z = 4) was refined by x-rays on a weakly twinned crystal prepd. in a Bi2O3/B2O3 flux with TiO2/Fe2O3 in stoichiometric proportions. The lattice consts. were orthorhombic with a 5.4318(6), b 41.149(4) and c 5.4691(12) .ANG.. Refinement in space group Fmm2 converged at R(Rw) = 4.6 (4.2%) with 538 averaged reflections. As the crystal showed <5% of twin domains, a supplementary powder refinement was performed to confirm space group Fmm2. The refinement gave confidential values R(Rw) = 3.1 (4.3%) and RBragg = 7.4%. No superstructure reflections were found. The structure is built up of layers, composed of 2 slightly and 2 strongly distorted perovskite units. These layers are sepd. by O layers. Birefringence, Dn, was restudied at room temp. on a wedge shaped crystal and found to be 0.080 +- 4. When studied as a function of temp. Dn revealed 2 phase transitions of 1st and 2nd order, at 560 and 750 Deg, resp. Based on the present structure detn. of the Fmm2 room temp. phase, on group subgroup considerations and polarized light microscopy studies, the following phase sequence is suggested: Fmm2 ->(I)-560 Deg-> Fmmm ->(II)-750 Deg-> I4/mmm. Etching of the crystal surface with concd. HCl produces typical etch figure alignments which point in the direction of the crystal axes a and c and form an angle of 45 Deg with the traces of the (101) domain walls.
Keywords Aurivillius phaseX-ray diffractionStructureOptical studiesEtch figures
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Structures
Project FNS: 1991
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KUBEL, Frank, SCHMID, Hans. X-ray room temperature structure from single crystal data, powder diffraction measurements and optical studies of the Aurivillius phase Bi5(Ti3Fe)O15. In: Ferroelectrics, 1992, vol. 129, n° 1-4, p. 101-112. https://archive-ouverte.unige.ch/unige:31381

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