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

The structure of CaTiO3 has been studied at high temperatures by powder neu tron diffraction methods. From inspection of the diffraction data two phase transitions are evident, with an intermediate tetragonal (I4/mcm) structur e forming near 1500 K and a primitive cubic (Pm (3) over bar m) structure a bove 1580 K. Detailed Rietveld analyses of the data suggest there may also be a phase transition from the room temperature Pbnm structure to an orthor hombic 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 e ntire temperature range.