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

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 296-1720K. 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) over barm 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 14/mcm-Pm (3) over barm transformation. These results indicate that the Pbnm-I4/mcm transition is of first order and that the I4/mcm-Pm (3) over barm transformation is of either second or higher order. (c) 2005 Elsevier Inc. All rights reserved.