Abstract
We explore the Bi(Zn$_{1/2}$Ti$_{1/2}$)O$_3$-La(Zn$_{1/2}$Ti$_{1/2}$)O$_3$-PbTiO$_3$ pseudoternary phase diagram using density functional theory and a solid solution model. We find a region of stability against phase segregation that contains a morphotropic phase boundary. Based on the results we identify a ferroelectrically active composition region that is likely to show strong electro-mechanical response. Furthermore, we find that La replacement for Bi not only lowers the polarization as might be expected, but also shifts the balance from tetragonality towards rhombohedral distortions. This may be of general use in modifying phase diagrams of $A$-site driven perovskite ferroelectric solid solutions to generate new morphotropic phase boundary systems.
