Determination of the space group of LaCrO₃ by convergent-beam electron diffraction

The space group of LaCrO₃ and its variation with temperature was analyzed by selected area electron diffraction (SAED) and by convergent-beam electron diffraction (CBED). All the reflection spots of SAED patterns of LaCrO₃ at room temperature could be indexed as orthorhombic symmetry with primitive lattice of a = 5.479, b = 5.516, and c = 7.766 angstroms. The space group of LaCrO₃ at room temperature was determined to be Pbnm (no. 62) from the analysis of CBED patterns. The reflection spots of SAED patterns which indicated orthorhombic symmetry disappeared with increase in temperature up to 300 °C. From CBED patterns, it was clarified that the crystal system of LaCrO₃ at 300 °C was rhombohedral with space group of R3̄c (no. 167).