“Unusual” phase transitions in CeAlO3

High-resolution time-of-flight neutron powder diffraction was carried out to investigate the crystal structures of CeAlO3 over a wide temperature range between 4.2 and 1423 K. Confirming the recent result of X-ray powder diffraction, the room temperature structure is tetragonal with the space group I4/mcm (tilt system (a0a0c−)). The tetragonal structure persists down to 4.2 K. However, above room temperature CeAlO3 undergoes three phase transitions: first to the orthorhombic Imma structure (tilt system (a0b−b−)) at, e.g., 373 K, then to the rhombohedral image structure (tilt system (a−a−a−)) at, e.g., 473 K, and finally, to the primitive cubic image structure which exists above 1373 K. The sequence of phases, image, which occurs in CeAlO3 is a rare one in oxide perovskites.