Misfit strain modulated phase structures of epitaxial Pb(Zr1−xTix)O3 thin films: The effect of substrate and film thickness

It is well known that the structures and properties of ferroelectric films can be remarkably different from their bulk counterpart, and a nonlinear phenomenological theory of ferroelectrics is applied to study phase structures and electromechanical properties of epitaxial Pb(Zr1−xTix)O3 (PZT) thin films, focusing on the effects of substrate and film thickness. The effective misfit strain induced by lattice mismatch between film and substrate has been calculated, and the misfit strain–composition, temperature–composition, and thickness–composition phase diagrams of PZT films have been constructed. The temperature–composition phase diagram differs substantially from that of bulk PZT ceramics, and the calculated phase structures in thin films allow us to explain numerous previous experimental observations. In particular, it is confirmed that the morphotropic phase boundary (MPB) of PZT films is shifted from that of bulk PZT, resulting in substantially different electromechanical response in PZT thin films. Good agreement with experimental data is observed in general.