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.

Graphical abstractNeutron 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 full-size imageDownload as PowerPoint slide