First principles prediction of a morphotropic phase boundary in the Bi(Zn1/2Ti1/2)O3−(Bi1/2Sr1/2)(Zn1/2Nb1/2)O3 alloy

The magnitude and direction of polarization within alloys of the tetragonally distorted Bi(Zn1/2Ti1/2)O3 (BZT) and the rhombohedrally oriented (Bi1/2Sr1/2)(Zn1/2Nb1/2)O3are explored using density functional theory. For compositions with ≥50% of BZT, we find that the polarization is mainly in the [001] direction. Conversely, for low concentrations of BZT the polarization is rhombohedrally oriented. Based on these results we propose a phase diagram with a monoclinic phase that appears when the BZT concentration is roughly 50%. At this concentration, the material may have a useful piezoelectric response.