Abstract
The structural phase transitions of the calcium titanate perovskite CaTiO 3 were investigated by the Rietveld analysis of high-temperature neutron and X-ray powder diffraction data in the temperature range of 296–1720 K. The present work demonstrates that the compound exhibits two reversible phase transitions of orthorhombic Pbnm-tetragonal I4/ mcm and of I4/ mcm-cubic Pm 3 ¯ m at 1498±25 K and 1634±13 K, respectively. No evidence of Cmcm phase is observed between the Pbnm and I4/ mcm structures. The lattice parameters discontinuously change at the Pbnm– I4/ mcm transition point, while a continuous change is observed for the I 4 / mcm – Pm 3 ¯ m transformation. These results indicate that the Pbnm– I4/ mcm transition is of first order and that the I 4 / mcm – Pm 3 ¯ m transformation is of either second or higher order.
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