Secrets of PZT

Lead zirconate titanate, Pb(Zr,Ti)O3 or PZT, is the best known and most important piezoelectric material. During the fifty years since its discovery its structure and properties have been studied in a great detail. Despite these efforts and the fact that PZT is used in innumerable devices its properties are still not well understood. PZT is not (widely) available in form of sufficiently large single crystals and its lattice properties are therefore inaccessible experimentally. PZT??s phase diagram has undergone a major modification a decade ago when a monoclinic phase was discovered in the morphotropic phase boundary region; this modification and the nature of the apparent monoclinic signature are now being a subject of intense debate. PZT is never used chemically pure in applications and its main modifications are in form of acceptor (hard) and donor (soft) doped materials. Our understanding of details of hardening and softening processes is, however, insufficient as demonstrated by recent studies of defect chemistry of hard and soft materials, showing a more complex defect structure than previously thought. In this presentation we shall review the recent advances in revealing the remaining secrets of PZT: the presence of the monoclinic phase, the nature of the morphotropic phase boundary, mechanisms and defects involved in hardening and softening, balance between domain wall and lattice contributions to the outstanding properties of PZT will be discussed.