High‐Temperature Phase Transitions in PbZrO ₃

Abstract

A high‐temperature X‐ray diffraction study of a high‐purity PbZrO 3 specimen at 25° to 236°C is reported. The symmetry of the perovskite sub‐cell of PbZrO 3 was determined unambiguously by observing the splitting of the line groups N = 12 and N = 16 when the diffraction pattern was indexed on the basis of the perovskite cell being a unit cell for the structure. Diffractometer studies were conducted of the N = 12 line group using Fe K α radiation and of the N = 16 line group using Cu K α radiation. The ferroelectric phase of PbZrO 3 possessed a rhombohedral sub‐cell with the angle α being acute. Stable two‐phase mixtures and considerable thermal hysteresis were observed at the antiferroelectric α ferroelectric transition temperature. A very weak “extra” diffraction line was observed in the diffraction patterns of the ferroelectric and paraelectric phases, indicating that the unit cells of these structures may be multiples of the perovskite subcell.