Mobility of Edge Dislocations in Single-Crystal Calcium Fluoride

Abstract

The mobility ν of edge dislocations in calcium fluoride has been measured over an applied stress τ range of 0.1–1.0 kg/mm² and from temperatures between 25° and 100°C. The data are fitted to the relationship $${\text{v=6×10}}^4\exp \text{[−(0.54\hspace{0.17em}}\mathrm{eV}\text{/kT)−(0.89\hspace{0.17em}}{\mathrm{kg/mm}}^2\mathrm{/\tau )]}\mathrm{cm/sec}$$ . The activation energy observed for dislocation mobility agrees with that for migration of fluorine ion vacancies in CaF₂. Oxygen impurity is observed to harden the crystals. Interactions between oxygen ion and fluorine ion‐vacancy dipoles and the dislocation strain fields are considered responsible for some of the velocity‐stress‐temperature behavior.