Monoclinic phases in the Pb(Zr_xTi_1-x)O₃ ceramics

Abstract

Following the recent report that the tetragonal phase of Pb(Zr_xTi_1-x)O₃ (PZT) with compositions close to the morphotropic phase boundary (MPB) transforms to a monoclinic phase with Cm space group at low temperatures, we reported yet another low temperature phase transition in which the Cm phase transforms to another monoclinic phase with Cc space group. We have shown that Cm to Cc phase transition is an antiferrodistortive (AFD) transition leading to superlattice reflections which are observable in the electron and neutron diffraction patterns only and not in the XRD patterns as a result of which the earlier workers missed the C_c phase in their high-resolution XRD studies at low temperatures. Rietveld analysis of high-resolution powder neutron diffraction data rules out the possibility of R3c space group, instead of Cc, for the superlattice phase.