Nonbasal Glide in Dislocation-Free Cadmium Crystals. II. The (112̄2) [1̄1̄23] System

Abstract

The (112̄2) [1̄1̄23] glide system was studied in thin, dislocation‐free cadmium platelets by transmission electron microscopy and compared with observations on zinc platelets. Screw dislocations with a ⅓ Burgers vector were formed at the edges of the crystal and moved primarily on {112̄2} planes. Elongated, sessile dislocation loops were formed on basal planes when screws developed large jogs during cross‐glide. Smaller numbers of secondary ⅓ dislocations were also formed and moved on basal planes. Observations in the temperature range −150° to +25°C showed that the behavior of the long loops and of the other dislocations in cadmium and zinc varied with temperature as follows: (1) At temperatures lower than ∼−120° in Cd and ∼−80° in Zn, the long loops were stable and practically no recovery took place. High densities of loops and networks of secondary dislocations were built up and hardened the crystal. (2) In the intermediate temperature range −120° to −40° for Cd and −80° to +10° for Zn, the long loops split up into rows of circular loops, which were then stable. The process involved the pipe‐diffusion of material around the long loops and required a lower activation energy than that for climb. Some of the circular loops were found to contain stacking faults. (3) At high temperature, above ∼−40° for Cd and ∼+10° for Zn, circular loops annealed out by climb with an activation energy ∼0.8 ev for Cd and ∼0.95 ev for Zn; secondary dislocation networks dispersed by climb; and the dislocation density, and therefore the work‐hardening, was small. At high beam intensities dislocation loops often grew by climb, probably as a result of the formation of point defects by ion bombardment, the ions being formed by the interaction between electrons and residual gas molecules.