PHASE-TRANSITION AND THERMAL-EXPANSION OF LACRO3 SOLID-SOLUTIONS

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 me asurement in the range of 25 to 800-degrees-C. Single-phase solid solu tions were obtained for the substitutions of Zn and Cu up to 20 and 15 %, respectively. The transition temperature from an orthorhombic struc ture to a rhombohedral structure was determined from the inflection of the thermal expansion curve. While the substitution of Sr decreased t he volume of the pseudocubic cell, lowering the transition temperature , the substitutions of Zn and Cu increased the volume, raising the tra nsition temperature. The tolerance factor seems to affect the transiti on behavior. The substitutions of Sr, Zn, Cu and Li resulted in an inc rease in the thermal expansion coefficient. The relation between the t hermal expansion coefficient and the melting point of component oxides as well as the transition temperature was discussed.