X-ray diffraction contrast of inversion twin boundaries in BeO crystals

Inversion twin boundaries in BeO crystals (wurtzite structure) can be studied by X-ray topography. They can be regarded as a special kind of stacking fault. The section topograph images of a twin boundary, lying parallel to the c axis, agree well with the theory for a single stacking fault. From the contrast variation of the images for various reflections, it is concluded that the oxygen sublattice on one side of the twin boundary is displaced from that on the other side by (1/16)[001] so that the oxygen layer parallel to the basal plane on one side is located at the center of the oxygen and beryllium layers on the other side. The image contrast in section topographs is very sensitive to the phase shift due to a fault. The phase shift of a few degrees can be detected easily. This sensitivity leads to an accurate structure determination of the inversion twin boundary.