On the origin of the large piezoelectric effect in morphotropic phase boundary perovskite single crystals

The high-field behavior of perovskite ferroelectrics close to a morphotropic phase boundary is investigated using the thermodynamic theory of ferroelectrics. For Pb(Zr0.55Ti0.45)O3, a phase transition from the rhombohedral to the tetragonal state is predicted for a critical field of approximately 4 MV m−1 parallel to the 〈001〉 axis. The transition is characterized by a strain of 0.015 parallel to 〈001〉. It is postulated that this transition is the origin of the large field-induced strains observed in single crystals of complex perovskite solid solutions with morphotropic phase boundaries. It is proposed that the transition is diffuse with respect to the applied field due to the inhomogeneity of the critical field arising from the B-site disorder in the complex perovskites. A simple random-field model illustrates the hypothesis.