Direct Observation of Covalency between O and Disordered Pb in Cubic PbZrO₃

In cubic PbZrO₃, which undergoes an antiferroelectric phase transition, the distinct disorder of Pb at twelve sites toward the neighboring O is detected for the first time by analyzing high-energy X-ray powder diffraction data. In the charge density distributions, the covalent nature of the Pb-O bond is also revealed, which proves the existence of electron hybridization between O and disordered Pb in cubic PbZrO₃. None of these structural characteristics of PbZrO₃ were found in the previously studied cubic PbTiO₃ structure [Y. Kuroiwa et al.: Phys. Rev. Lett. 87 (2001) 217601], which undergoes a ferroelectric phase transition. This may be a clue to understanding why PbTiO₃ and PbZrO₃ respectively show ferroelectric and antiferroelectric phase transitions.