Prismatic Dislocation Loops in Cold-Worked and Annealed MgO Crystals

Abstract
Plastic deformation introduces elongated edge‐dislocation loops into MgO crystals. Annealing at 1200° to 1500°C does not entirely remove this damage, even close to a free surface. Instead, relatively large circular vacancy loops are derived from the elongated loops. Successive anneals increase the mean diameter of the loops and reduce their number. In crystals which had been heavily strained by repeated bending the mean diameter increased linearly with total annealing time, within the limits 500 to 2000 Å. Loop growth is interpreted as being due to the production of vacancies by plastic flow, in a concentration of at least 10−6 for each 1% strain.