Disorder of Pb Atom in Cubic Structure of Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ System

Abstract

The crystal structures of (1-x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–PT: 0≤x≤0.3) in the cubic phase at 650 K have been investigated by analyzing the high-energy synchrotron-radiation (SR) powder diffraction data using the Rietveld method. It is found that the Pb atom does not settle at the ideal high-symmetry position with a harmonic thermal parameter. The split-atom method reveals that the Pb atom in the cubic phase is disordered and settles randomly at crystallographically equivalent positions slightly off-center of the cubic-corner site. The disordered directions of the Pb atom are significantly changed at the concentration x∼0.15. This structural boundary found in the cubic phase is related to the appearance of the morphotropic phase boundary (MPB).