Dislocations and impurity boundaries in zing crystals grown from the melt

Abstract

The distribution of etch pits at microsegregations produced by constitutional supercooling was investigated using progressive polishing and etching techniques. Crystals which exhibit an elongated cellular segregation structure commonly called “corrugation” structure have associated with them rows of etch pits. The density of etch pits, their rearrangement into walls and their formation into networks behind the interface suggests that the etch pits reveal the ends of decorated dislocations introduced at the segregation boundaries to accommodate the lattice strain. Networks form when the dislocations are set free as homogenization occurs behind the solid-liquid interface. The dislocations then become arranged into walls perpendicular to the {0001}. This secondary substructure fully developed 3 mm behind the solid-liquid interface increases in size as the crystal continues to grow and the dislocations climb and glide in agreement with predictions made by Tiller (1).