Investigating phase transitions in ABO₃perovskites using perturbed angular correlation spectroscopy

Abstract

Abstract Perturbed Angular Correlation (PAC) measurements were performed at several temperatures on BaTiO3, SrTiO3, BaHfO3 ceramic and PbTiO3 powder samples. In the PbTiO3 and BaTiO3 samples, both the tetragonal (ferroelectric) and the cubic (paraelectric) phases were investigated. For the tetragonal phase temperatures, the perturbation functions for PbTiO3 show strongly decreasing electric field gradients (efgs) and increasing linebroadening with increasing temperature. These two features are evidence for an order-disorder phase transition mechanism. Although the data for tetragonal BaTiO3 provide less information, linebroadening is evident, which is not inconsistent with an order-disorder mechanism. Above the Curie temperatures, both compounds show featureless perturbation functions that decay slowly with increasing time. In addition, this interaction shows little temperature sensitivity. Similarly, PAC measurements on cubic BaHfO3 and cubic SrTiO3 show this behavior. The literature reports similar phenomena for cubic PbZrO3 and cubic PbHfO3, although the explanations differ from report to report. These results suggest that a nuclear spin relaxation mechanism was responsible for the perturbations.