Electron Charge Density Study on Antiferroelectric Phase Transition in PbZrO3

Electron charge density distributions of PbZrO 3 both in the paraelectric and antiferroelectric phases are investigated at 520 and 100 K, respectively, by analyzing the high-energy synchrotron-radiation (SR) powder diffraction data utilizing the maximum entropy method (MEM)/Rietveld method. A clear evidence to show that the Pb atom in the paraelectric phase is disordered in the ⟨ 110⟩ directions and forms covalent bonds with the neighboring twelve O atoms is revealed. In the antiferroelectric phase, the Pb atoms are ordered alternately parallel and antiparallel to the direction, which allows the formation of strong covalent bonds on the shortened Pb─O bonds. Anisotropic thermal motion of the O atoms in the paraelectric phase is observed, which implies the rotation of ZrO 6 octahedra at the antiferroelectric phase transition.