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Layered Intergrowth Phases Bi4MO8X(X=Cl,M=Ta andX=Br,M=Ta or Nb): Structural and Electrophysical Characterization

Authors
Journal
Journal of Solid State Chemistry
0022-4596
Publisher
Elsevier
Publication Date
Volume
166
Issue
1
Identifiers
DOI: 10.1006/jssc.2002.9572

Abstract

Abstract The high-temperature structural behavior of the layered intergrowth phase Bi 4TaO 8Cl, belonging to the Sillén-Aurivillius family, has been studied by powder neutron diffraction. This material is ferroelectric, space group P2 1 cn, at T C<640 K. An order–disorder transition to centrosymmetric space group Pmcn is found around 640 K, which involves disordering of TaO 6 octahedral tilts. A second phase transition, of a first-order nature, to space group P4/ mmm occurs at a temperature of ∼1038 K. The crystal structures of the bromide analogs Bi 4 MO 8Br ( M=Nb, Ta) have also been determined at room temperature; both are isomorphous with Bi 4TaO 8Cl and exhibit maxima in dielectric constant at temperatures of approximately 588 and 450 K, respectively.

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