DETERMINATION OF STRUCTURE FACTORS OF AL2O3 BY MEANS OF LARGE-ANGLE CONVERGENT-BEAM ELECTRON-DIFFRACTION

Intensities of higher order reflections in a large angle convergent be am electron diffraction (LACBED) pattern are measured for alpha-Al2O3 and are compared with theoretical calculations in order to examine app licability of the kinematical approximation to determination of the st ructure factors. Effects of specimen thickness, temperature and absorp tion on the intensities are investigated through the dynamical theory of electron diffraction. A static displacement of Al3+ ions from their ideal positions in a unit cell of alpha-Al2O3 is determined from a re lative change between two neighbouring high index reflections. The dis placement determined through the kinematical theory of electron diffra ction agrees well with the one through the dynamical theory and the on es measured by X-ray or neutron diffraction. The result demonstrates t he usefulness of LACBED and the kinematical approximation.