Theoretical Prediction of New High-Performance Lead-Free Piezoelectrics

We predict the occurrence of large ferroelectric polarization and piezoelectricity in the hypothetical perovskite-structure oxides, bismuth aluminate (BiAlO 3 ) and bismuth gallate (BiGaO 3 ), using density functional theory within the local density approximation. We show that BiGaO 3 will have a similar structure to PbTiO 3, although with much stronger tetragonal distortion and therefore improved ferroelectric properties. Likewise, BiAlO 3 shares structural characteristics with antiferrodistortive PbZrO 3, but it is also a ferroelectric with large polarization. Therefore, we propose the Bi(Al,Ga)O 3 system as a replacement for the widely used piezoelectric material, Pb(Zr,Ti)O 3 (PZT), that will avoid the environmental toxicity problems of lead-based compounds. Finally, we show that, in both BiAlO 3 and BiGaO 3, the large distortions from the prototypical cubic structure are driven by the stereochemical activity of the Bi lone pair.