Characterisation of the SOFC material, LaCrO3, using vibrational spectroscopy

Abstract

LaCrO3 is reported to undergo a low to high temperature (HT) phase transition from orthorhombic (Pnma) to rhombohedral (R-3c), at ca. 255 degreesC. The phases involved in the low temperature phase transition of LaCrO3 have been determined using Raman spectroscopy at temperatures from -196 to 300 degreesC. There are nine Raman bands observed from a total of 24 predicted modes, seven of which are assigned from comparison with the Raman profile and relative band positions observed and calculated for the isostructural compound, YMnO3, as follows: 131(B-2g), 150(B-3g), 174(A(g)), 252(B-1g), 279(A(g)), 441 (A(g)) and 590(A(g)) cm(-1). A phase transformation was observed at ca. 260 degreesC from the change in the Raman profile. The high temperature rhombohedral phase of LaCrO3 had four bands which are assigned as follows: 58(E-g), 161 (E-g), 288(A(1g)) and 434(E-g, E-g) cm(-1), from comparison with the Raman profile and relative band positions observed for the isostructural compound, NdAlO3. The Fourier transform infrared (FTIR) spectrum of LaCrO3 showed a total of eight bands discernible at room temperature from 25 predicted modes for the orthorhombic structure. The mode assignments were determined by comparison with the Raman profile and relative band positions observed and calculated for the isostructural compound, SmAlO3, as follows: 138(B-2u), 166(B-3u), 197(B-1u), 240(B-3u), 266(B-2u): 332(B-2u), 357(B-2u), 381(B-3u), 425(B-3u), 446(B-1u), 471(B-3u), 493(B-3u), 573(B-1u), 606(B-3u) and 670 (B-1u)cm(-1). (C) 2004 Elsevier B.V. All rights reserved.