Phase Transition and Thermal Expansion of LaCrO₃ Solid Solutions

Abstract

Perovskite-type LaCrO₃ ceramics substituted with Sr on the La site and with Zn, Cu and Li on the Cr site were prepared and investigated by X-ray diffraction analysis at room temperature and thermal expansion measurement in the range of 25 to 800°C. Single-phase solid solutions were obtained for the substitutions of Zn and Cu up to 20 and 15%, respectively. The transition temperature from an orthorhombic structure to a rhombohedral structure was determined from the inflection of the thermal expansion curve. While the substitution of Sr decreased the volume of the pseudocubic cell, lowering the transition temperature, the substitutions of Zn and Cu increased the volume, raising the transition temperature. The tolerance factor seems to affect the transition behavior. The substitutions of Sr, Zn, Cu and Li resulted in an increase in the thermal expansion coefficient. The relation between the thermal expansion coefficient and the melting point of component oxides as well as the transition temperature was discussed.