Ferroelectric Behavior of PZT-BCO-BFO Solid Solutions

The ferroelectric behavior of 75% PbZr_0.5Ti_0.5O₃ - 25% BiMO₃ (where M=Fe,Co) (PZT-BMO) was studied using first principles density functional theory calculations. Despite the large rhombohedral and tetragonal polar distortions expected for the BiFeO₃ (BFO) and
BiCoO3 (BCO) end members, respectively, we find that both solid solutions retain the monoclinic phase of PZT. Furthermore, unlike the BCO and BFO end members that have large polarizations, the polarization for the PZT-BCO solid solution was determined to be 0.6 C/m2, closer to that of PZT. Combining our results with previous work on the BCO-BFO solid solution, we are able to suggest a phase diagram where PZT rich compositions retain the monoclinic phase present at the morphotropic phase boundary in PZT. Together, these results suggest the possibility of enhanced electromechanical responses for compositions of PZT-BMO with less than 75% PZT; thereby providing a novel route to designing high performance piezoelectrics with reduced Pb content.