Piezoelectric properties of perovskite ferroelectrics: Unsolved problems and future research

This article reviews recent advances in the studies of the piezoelectric properties of perovskite materials. Perovskite compositions are the best known and the largest family of ferroelectric and piezoelectric materials.: The dependence of the longitudinal, d(33), piezoelectric:coefficient on crystallographic orientation was examined in single crystals of BaTiO3, PbTiO3, Pb(Zr,Ti)O-3, KNbO3, relaxor-ferroelectric solid solutions [e.g. Pb(Mg1/3Nb2/3)O-3-PbTiO3 and Pb(Zn1/3Nb2/3)O-3-PbTiO3] and Na1/2Bi1/2TiO3. In most cases the largest piezoelectric coefficient was found in a direction which does not coincide with the polarization direction. In relaxer ferroelectrics, some compositions near the morphotropic phase boundary (MPB) exhibit very large piezoelectric (> 2000 pC/N) and coupling coefficients (k(33)> 90%) These results are-discussed in terms of so-called engineered domain structure and crystal anisotropy. The article also discusses evidence for the presence of a monoclinic phase between the rhombohedral and tetragonal phases at the MPB in Pb(Zr, Ti)O-3.