Phase transitions in perovskite at elevated temperatures - A powder neutron diffraction study

The structure of CaTiO₃ has been studied at high temperatures by powder neutron diffraction methods. From inspection of the diffraction data two phase transitions are evident, with an intermediate tetragonal (14/mcm) structure forming near 1500 K and a primitive cubic (Pm3̄m) structure above 1580 K. Detailed Rietveld analyses of the data suggest there may also be a phase transition from the room temperature Pbnm structure to an orthorhombic Cmcm structure around 1380 K. A remarkable feature of the results is the regular variation in the out-of-phase octahedral tilt angle over the entire temperature range.