Study On High Temperature Phase Transformation And Thermal Expansion Properties Of Perovskite CaTiO 3

Perovskite are the compounds which have the same structure as the mineral perovskite CaTiO₃, it has received more and more attention in the past few decades because of its diversity of physical and chemical properties. Perovskites represent prime device materials with applications in a wide variety, including solid fuel cell, pyroelectric sensors, high-temperature heating materials and immobilizing high-level radioactive waste, and have become the hot topic in the field of physics and chemistry.From a geological point of view, perovskites are also of important research value, and many important properties are still undiscovered. Liu（1974） proves that（Mg,Fe）SiO₃ perovskite are the major components of the lower mantle, and it may account for 70-90% of the total（Jackson and Rigden, 1998）. But due to its very low thermal stability（Madon et al. 1989）, experimental accuracy could not be met under the current technology. CaTiO₃ with high thermal stability and same structure with（Mg,Fe）SiO₃ perovskite then becomes a good substitute.CaTiO₃ is considered to be the orthorhombic Pbnm phase at room temperature and ambient pressure, and the pervious researchers argued about the findings of its high temperature properties and phase transformation behavior with increasing temperature. In this study, the structure of Synthetic CaTiO₃ were investigated by high temperature powder X-ray diffraction（XRD） in the temperature range at 300-1580 K. The results indicated that the Pbnm-I4/mcm transition occured at 1300-1350 K, and the transition was of first order. The orthorhombic Cmcm phase was not be observed, which supported the conclusion by Yashima and Ali（2009）. The thermal expansion coefficients of CaTiO₃ were calculated at room temperature, and the cell refinements were done by using the XRD data. These properties could be interpreted by their structures.