CRYSTAL STRUCTURE ANALYSIS OF LaCrO_3 SYSTEM Ⅰ. SPACE GROUP DETERMINATION BY CONVERGENT-BEAM ELECTRON DIFFRACTION

摘要

Crystal system of LaCrO_3 was analyzed with selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED). All the reflection spots of SAED patterns of LaCrO_3 at room temperature could successfully be indexed as orthorhombic symmetry with primitive lattice of a=5.479 A, b=5.516 A and c=7.766 A. The space group of LaCrO_3 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 of temperature up to 300℃. From CBED patterns, it was clarified that the crystal system of LaCrO_3 at 300℃ was rhombohedral with space group of R3c (No. 167).