Theoretical prediction of new high-performance lead-free piezoelectrics

Abstract

We predict the occurrence of large ferroelectric polarization and piezoelectricity in the hypothetical perovskite-structure oxides, bismuth aluminate (BiAlO₃) and bismuth gallate (BiGaO₃), using density functional theory within the local density approximation. We show that BiGaO₃ will have a similar structure to PbTiO₃, although with much stronger tetragonal distortion and therefore improved ferroelectric properties. Likewise, BiAlO₃ shares structural characteristics with antiferrodistortive PbZrO₃, but it is also a ferroelectric with large polarization. Therefore, we propose the Bi(Al,Ga)O₃ system as a replacement for the widely used piezoelectric material, Pb(Zr,Ti)O₃ (PZT), that will avoid the environmental toxicity problems of lead-based compounds. Finally, we show that, in both BiAlO₃ and BiGaO₃, the large distortions from the prototypical cubic structure are driven by the stereochemical activity of the Bi lone pair.