Enhanced ferroelectric polarization and potential morphotrophic phase boundary in PZT-based alloys

We present a combined theoretical and experimental study of alloys of the high performance piezoelectric PZT (PbZr$_{0.5}$Ti$_{0.5}$O$_{3}$) with BZnT (BiZn$_{0.5}$Ti$_{0.5}$O$_{3}$) and BZnZr (BiZn$_{0.5}$Zr$_{0.5}$O$_{3}$), focussing on lattice instabilities, atomic displacements and ferroelectric polarization. From theory we find that the 75 - 25 PZT - BZnT alloy has substantially larger cation displacements, and hence ferroelectric polarization than the PZT base material, on the tetragonal side of the phase diagram. We also find a possible morphotrophic phase boundary in this system by comparing displacement patterns and optimized c/a ratios. Experiments indicate the feasibility of sample synthesis within this alloy system.