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

Crystal structure and structural phase transition of LaCrO3 have been inves tigated by using various diffraction technique. X-ray diffraction at high t emperature revealed that the crystal structure of LaCrO3 below 240 degrees C and above 280 degrees C is orthorhombic- and rhombohedral-distorted perov skite, respectively. The discrete volume compression was observed at the ph ase 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 temperatur es was carried out using the space group determined by the electron diffrac tion. It was revealed that the volume compression at the phase transition w as principally due to the shrinkage of the [CrO6] octahedra. DSC-XRD simult aneous measurements indicated that the phase transition started at about 25 0 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 th an orthorhombic or rhombohedral was observed at the phase transition. (C) 2 000 Elsevier Science B.V. All rights reserved.