Determination of the Burgers vector of perfect dislocations observed by X-ray topography in hexagonal single crystals

Individual dislocations were observed in high-quality cadmium and zinc single crystals by means of transmission X-ray topography. The contrast of their images was characterized on the topographs as a function of the direction of the line, the Burgers vector and the diffraction vector. In addition, the theoretical contrast of perfect dislocations with all the possible Burgers vectors of the hexagonal lattice was computed by using a program which takes into account the crystal anisotropy. The comparison of experimental and theoretical results showed unambiguously that the long dislocation lines contained in the crystals have an a-type Burgers vector, while the loops and spiral dislocations have either a c- or c + a-type Burgers vector.