High-energy SR powder diffraction evidence of multisite disorder of Pb atom in cubic phase of PbZr1-xTixO3

High-energy synchrotron-radiation (SR) powder diffraction experiments have been carried out to investigate the relationship between the crystal structure of the paraelectric phase in PbZr1-xTixO3 (PZT) and phase transition. The Rietveld refinement adopting the split-atom method reveals that the Pb atom in PZT, except PbTiO3 (x = 1), is settled at multisites in relevant directions from the corner site of an ideal cubic structure. Namely, the Pb atom is found to be disordered at 12 sites in the 110 directions in PbZrO3 (x = 0), and at 8 sites in the 111 directions in the Zr-rich region (0 < x < 0.5). The disordered motion of the Pb atom markedly changes at x = 0.5, and the (110) disorder is preferable in the Ti-rich region (0.5 < x < 1). The disordered characteristics of the Ph atom and the structural boundary observed at x = 0.5 in the paraelectric phase are significant for understanding of the mechanism of the order-disorder phase transition and appearance of a morphotropic phase boundary (MPB) in PZT.