The missing boundary in the phase diagram of PbZr1−xTixO3

PbZr 1−x Ti x O 3 (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 (M A ) structure and another monoclinic (M B ) structure has been found. The general advantage of a particular monoclinic distortion (M A ) 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. PbZr 1−x Ti x O 3 is 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.