Space group and crystal structure of the Perovskite CaTiO3 from 296 to 1720 K

The structural phase transitions of the calcium titanate perovskite CaTiO3 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 image 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 image transformation. These results indicate that the Pbnm–I4/mcm transition is of first order and that the image transformation is of either second or higher order.