''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 1423K. 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 4.2K. However, above room temperature CeAlO3 undergoes three phase transitions: first to the orthorhombic Imma structure (tilt system (a0b-b-)) at, e.g., 373K, then to the rhombohedral R3-bar c structure (tilt system (a-a-a-)) at, e.g., 473K, and finally, to the primitive cubic Pm3-bar m structure which exists above 1373K. The sequence of phases, Pm3-bar m->R3-bar c->Imma->I4/mcm, which occurs in CeAlO3 is a rare one in oxide perovskites