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 Pm3¯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 I4/mcm–Pm3¯m transformation. These results indicate that the Pbnm–I4/mcm   transition is of first order and that the I4/mcm–Pm3¯m transformation is of either second or higher order.

Neutron diffraction patterns of CaTiO3 measured at different temperatures. Filled circles and triangles denote the peaks that disappear due to the Pbnm-to-I4/mcm   and I4/mcm‐to‐Pm3¯m phase transitions, respectively. A sequence of two transformations was confirmed: OrthorhombicPbnm↔1498±25KTetragonalI4/mcm↔1634±13KCubicPm3¯mFigure optionsDownload as PowerPoint slide