Pressure and Temperature Dependence of the Dielectric Properties and Phase Transitions of the Antiferroelectric Perovskites: PbZrO3and PbHfO3

Abstract

Hydrostatic-pressure measurements have shown that in PbZr${\mathrm{O}}_{3}$ the antiferroelectric (AFE)-paraelectric (PE) transition temperature ${T}_{a}$ increases ($\frac{d{T}_{a}}{\mathrm{dP}}=4.5\ifmmode\pm\else\textpm\fi{}0.3\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}/\mathrm{kbar}$) whereas the extrapolated Curie-Weiss temperature ${T}_{0}$ decreases $\frac{d{T}_{0}}{\mathrm{dP}}=\ensuremath{-}16.0\ifmmode\pm\else\textpm\fi{}0.5\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}/\mathrm{kbar}$ with increasing pressure. Interpreted in terms of the lattice dynamics, the results give the first experimental evidence that there are two independent low-frequency temperature-dependent lattice vibrational modes in PbZr${\mathrm{O}}_{3}$: a ferroelectric (FE) mode which determines the large polarizability and the Curie-Weiss behavior of the static dielectric constant in the paraelectric phase, and an AFE mode (probably a coupled mode) which causes the AFE transition. On cooling, the crystal becomes unstable against the AFE mode at ${T}_{a}$ just before the instability due to the FE mode is reached at ${T}_{0}$. Pressure increases the frequency of the FE mode but decreases ("softens") that of the AFE mode, and consequently, the static-dielectric-constant anomaly at the transition decreases sharply. The behavior of PbHf${\mathrm{O}}_{3}$ is qualitatively similar to that of PbZr${\mathrm{O}}_{3}$, but is complicated by the presence of two AFE phases at 1 bar. A third AFE phase becomes…