SPACE-GROUP DETERMINATION AND STRUCTURE MODEL FOR KAPPA-AL2O3 BY CONVERGENT-BEAM ELECTRON-DIFFRACTION (CBED)

The crystal structure of kappa-Al2O3, which was produced by chemical vapour deposition, has been examined by convergent-beam electron diffraction combined with selected-area electron diffraction and high-resolution electron microscopy. The crystal structure of kappa-Al2O3 has been found to be orthorhombic, space group Pna2(1). The lattice parameters are a = 4.69, b = 8.18 and c = 8.87 angstrom. The volume is 340.3 angstrom 3 and the density is approximately 3.98 g cm-3, Z = 8. Three different variants of kappa-Al2O3 domains give rise to a false superlattice which can be described by a hexagonal structure. An atomic model for kappa-Al2O3 based on the experimental results has been constructed.