Neutron diffraction topographic observation of the {100}-layer substructure in a Cu-5% Ge single crystal

Abstract

Neutron diffraction topography has been applied to the direct observation of the texture in Bridgman-grown Cu-5% Ge crystals with growth direction nearly parallel to [110]. The texture is composed of a layer substructure, constituting a hierarchy in the crystal texture: layers parallel to (001) are arrayed with the spacing of about 1 mm, and extend throughout the crystal nearly parallel to the growth direction. The (001)-layers are attached on both sides with plates parallel to (100)- and (010)-planes. These layer substructures correspond to the arrayed striations visible on the crystal surfaces. The substructure is different from both the cellular and the lineage substructures hitherto proposed to describe the texture of Bridgman-grown crystals. The model suggests a new type of growth mechanism along three kinds of {100}-planes. The novel techniques of neutron diffraction topography are described. In the Appendix, the observed image contrast of the topographs is shown to be explained by the diffraction theory of the secondary extinction.