Cation disorder in ferroelectric PbBi2Nb2O9
- 1 June 1996
- journal article
- research article
- Published by International Union of Crystallography (IUCr) in Acta crystallographica Section B, Structural science, crystal engineering and materials
- Vol. 52 (3) , 432-439
- https://doi.org/10.1107/s0108768195015072
Abstract
The ferroelectric Curie temperature, Tc , of PbBi2Nb2O9 was found to shift from 833 K in samples slowly cooled from 1373 K to Tc 's up to 883 K when the samples were quenched from various temperatures in the range 973–1373 K. The variation of Tc with heat treatment was fully reversible. Extra Raman modes appear and the width of some Raman bands change as a function of heat treatment. These results are interpreted in terms of cation order–disorder involving the Pb2+ and Bi3+ ions in the perovskite units and the Bi2O2 layer. Neutron Rietveld analyses of the structures (orthorhombic, A21 am, Z = 4, λ = 1.216) indicate a possible change in cationic order–disorder, with Pb2+ ions preferentially occupying the perovskite A-sites to the extent of 91 (7) and 80 (7)%, respectively, in the quenched and slowly cooled samples.Keywords
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