High-Energy SR Powder Diffraction Evidence of Multisite Disorder of Pb Atom in Cubic Phase of PbZr 1-x Ti x O 3

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 PbZr 1- x Ti x O 3 (PZT) and phase transition. The Rietveld refinement adopting the split-atom method reveals that the Pb atom in PZT, except PbTiO 3 ( 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 PbZrO 3 ( 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 Pb 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.