'Unusual' phase transitions in CeAlO3

摘要

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 (a(0)a(0)c(-))). 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 (a(0)b(-)b(-))) at, e.g., 373 K, then to the rhombohedral R (3) over barc structure (tilt system (a(-)a(-)a(-))) at, e.g., 473 K, and finally, to the primitive cubic Pm (3) over barm structure which exists above 1373 K. The sequence of phases, Pm (3) over barm -> R (3) over barc -> Imma -> I4/mcm, which occurs in CeAlO3 is a rare one in oxide perovskites. (c) 2006 Elsevier Inc. All rights reserved.