Structures and phase transitions in Sr1−xBaxHfO3 perovskites

Abstract

Variable temperature synchrotron powder diffraction methods have been used to study the structures and phase transitions in a series of perovskites of composition Sr_1−xBa_xHfO₃. We find that increasing the Ba content results in a transition from the orthorhombic Pnma type structure to the cubic Pmmvia two intermediate phases, Imma and I4/mcm, as follows:The identification of the correct symmetry has relied on a combination of the observed splitting of the main Bragg reflections and the systematic absence of weak superlattice reflections. Variable temperature diffraction measurements have been used to establish the nature of the various phase transitions (continuous or first order) and these generally are consistent with group theoretical analysis. Unusual behavior is observed for the two compositions Sr_0.5Ba_0.5HfO₃ and Sr_0.8Ba₂HfO₃ at low temperatures.