Distinctive Charge Density Distributions of Perovskite-Type Antiferroelectric Oxides PbZrO₃and PbHfO₃in Cubic Phase

Abstract

The electron charge density distributions of simple perovskite oxides, Pb B O 3 ( B = Ti, Zr and Hf), in their cubic phase are investigated by analyzing high-energy synchrotron powder diffraction data by the maximum entropy method (MEM)/Rietveld method. Clear structural differences between the antiferroelectric and ferroelectric perovskites are revealed. In the cubic phase of PbZrO 3 and PbHfO 3 that undergo antiferroelectric phase transitions, the Pb atom is disordered around the special Wyckoff position. The thermal motion of the O atom is anisotropic, and the charge density distributions around the O atom are extended in the directions perpendicular to the Zr(Hf)-O covalent bond. None of these structural characteristics are observed in the cubic phase of PbTiO 3 that undergoes ferroelectric phase transition. The distinctive structural features observed in PbZrO 3 and PbHfO 3 should provide a clue to the mechanism of antiferroelectric phase transition.