Study of Defect Structures in BeO Single Crystals by X-Ray Diffraction Topography

Abstract

X-ray diffraction topography methods and supplementary optical microscopy were used to examine pyramidal and prismatic BeO crystals grown from lithium molybdate flux. The crystals appeared to have a high degree of perfection in that few dislocation lines were observed. Several specific types of defect structures were observed, however, in most of the crystals studied. The inversion-twin core structure was visible by image contrast effects from the twin boundary as well as by unequal image contrast on either side of the boundary. A screw dislocation line, possibly a group of many dislocations, commonly was present in the core and ran the full length of the crystal. Growth strata parallel to the active growth surfaces were also present. The topographs also revealed that considerable surface damage can be inflicted by intercrystal abrasion, much of which is removed by thermal annealing.