Ferroelectricity in (M=Al and Ga) with the structure

We report on the dielectric properties of bismuth aluminate and gallate with Bi:Al(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 I23) with a ∼ 10.18 Å rather than in the perovskite structure. This cubic phase is related to the γ - Bi 2 O 3 structure which has the actual chemical formula Bi 24 3 + ( Bi 3 + Bi 5 + ) O 40 − δ . In the aluminates and gallates studied by us, the Al and Ga ions are distributed over the 24 f and 2 a sites. These compounds exhibit ferroelectric hysteresis at room temperature with a weak polarization.