Röntgentopographische untersuchungen von gitterstörungen in Benzil-Einkristallen

Abstract

The defect structures in single crystals of benzil C6H5·CO·CO·C6H5 (space groups P312 and P322) grown by evaporation from a solution in xylol are examined by X-ray topography. Large parts of the crystals are highly perfect: the density of the defects is low, pendellosung fringes and other dynamical effects are observed. The crystals are divided into growth sectors grown onthe faces {1100}, {1102}, {1101} and {0001}. In addition to growth sector boundaries there are distinct growth layers. The growth sectors are identical with the regions of optical anomaly. The topographs show many rectilinear dislocation lines radiating from the nucleus and from inclusions and ending at the surface of the crystal. Their Burgers vectors are parallel to the threefold [001] or to one of the twofold axes of the crystal. Most of them have a predominant screw component. When passing through a growth sector boundary lines of -dislocations are deflected into directions parallel to the basal plane (0001) with an inclination of 17–20° towards the growth direction and 10–13° towards . These directions contain the maximum occurence of -dislocation lines are assumed to have a minimum potential energy per unit length in the growth direction. The crystals contain inclusions of matrix solution surrounded by a region of highly disturbed crystalline substance. They are frequently observed in (0001)-growth sectors and occur in connection with growth sector boundaries.