Analysis of crystal structure and phase transition of LaCrO3 by various diffraction measurements

Crystal structure and structural phase transition of LaCrO3 have been investigated by using various diffraction technique. X-ray diffraction at high temperature revealed that the crystal structure of LaCrO3 below 240 degrees C and above 280 degrees C is orthorhombic- and rhombohedral-distorted perovskite, respectively. The discrete volume compression was observed at the phase transition from orthorhombic to rhombohedral phase. The space group of LaCrO3 below 240 degrees C was determined to be Pbnm (No. 62), whereas that above 280 degrees C was R (3) over bar c (No. 167) by using selected area electron diffraction and convergent-beam electron diffraction. The Rietveld refinement of neutron diffraction patterns of LaCrO3 at various temperatures was carried out using the space group determined by the electron diffraction. It was revealed that the volume compression at the phase transition was principally due to the shrinkage of the [CrO6] octahedra. DSC-XRD simultaneous measurements indicated that the phase transition started at about 250 degrees C and was completed at about 268 degrees C with heating rate of 5 degrees C/min involving absorption of heat. No intermediate phase other than orthorhombic or rhombohedral was observed at the phase transition. (C) 2000 Elsevier Science B.V. All rights reserved.