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

We present a combined theoretical and experimental study of alloys of the high performance piezoelectric PZT (PbZr0.5Ti0.5O3) with BZnT (BiZn0.5Ti0.5O3) and BZnZr (BiZn0.5Zr0.5O3), focusing on atomic displacements, ferroelectric polarization, and elastic stability. 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. Elastic stability calculations find the structures to be essentially stable. Experiments indicate the feasibility of sample synthesis within this alloy system, although measurements do not find significant polarization, probably due to a large coercive field.