Ferroelectricity in Bi26-xMxO40-delta (M = Al and Ga) with the gamma-Bi2O3 structure

We report on the dielectric proper-ties of bismuth aluminate and gallate with Bi:AI(Ga) ratio of 1: 1 and 12:1 prepared at high temperature and ambient pressure. These compounds crystallize in a noncentrosymmetric body-centered cubic structure (space group 123) with a similar to 10.18 angstrom rather than in the perovskite structure.This cubic phase is related to the gamma-Bi2O3 structure which has the actual chemical formula Bi-24(3+) (Bi3+Bi5+)O40-delta. In the aluminates and gallates studied by us, the Al and Ga ions are distributed over the 24f and 2a sites. These compounds exibit ferroclectric hysteresis at room temperature with a weak polarization. (c) 2006 Elsevier Ltd. All rights reserved.