Distinctive charge density distributions of perovskite-type antiferroelectric oxides PbZrO₃ and PbHfO₃ in cubic phase

The electron charge density distributions of simple perovskite oxides, PbBO₃ (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 PbZrO₃ and PbHfO₃ 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)-O₃ covalent bond. None of these structural characteristics are observed in the cubic phase of PbTiO₃ that undergoes ferroelectric phase transition. The distinctive structural features observed in PbZrO₃ and PbHfO₃ should provide a clue to the mechanism of antiferroelectric phase transition.