The missing boundary in the phase diagram of PbZr1−xTixO3

PbZr1−xTixO3 (PZT) is one of the most important and widely used piezoelectric materials. The study of its local and average structures is of fundamental importance in understanding the origin of its high-performance piezoelectricity. Pair distribution function analysis and Rietveld refinement have been carried out to study both the short- and long-range order in the Zr-rich rhombohedral region of the PZT phase diagram. The nature of the monoclinic phase across the Zr-rich and morphotropic phase boundary area of PZT is clarified. Evidence is found that long-range average rhombohedral and both long- and short-range monoclinic regions coexist at all compositions. In addition, a boundary between a monoclinic (MA) structure and another monoclinic (MB) structure has been found. The general advantage of a particular monoclinic distortion (MA) for high piezoactivity is discussed from a spatial structural model of susceptibility to stress and electric field, which is applicable across the wide field of perovskite materials science. PbZr1−xTixO3is a widely used piezoelectric material. Here, the authors clarify the long-standing issue of the monoclinic crystal phase evolution across the morphotropic phase boundary in the compound’s phase diagram, contributing also to the understanding of its piezoelectric properties.