Structure model of γ-Al 2 O 3 based on planar defects.

The defect structure of γ-Al2 O3 derived from boehmite was investigated using a combination of selected-area electron diffraction (SAED) and powder X-ray diffraction (XRD). Both methods confirmed a strong dependence of the diffraction line broadening on the diffraction indices known from literature. The analysis of the SAED patterns revealed that the dominant structure defects in the spinel-type γ-Al2 O3 are antiphase boundaries located on the lattice planes , which produce the sublattice shifts . Quantitative information about the defect structure of γ-Al2 O3 was obtained from the powder XRD patterns. This includes mainly the size of γ-Al2 O3 crystallites and the density of planar defects. The correlation between the density of the planar defects and the presence of structural vacancies, which maintain the stoichiometry of the spinel-type γ-Al2 O3 , is discussed. A computer routine running on a fast graphical processing unit was written for simulation of the XRD patterns. This routine calculates the atomic positions for a given kind and density of planar defect, and simulates the diffracted intensities with the aid of the Debye scattering equation.