Creep in Vacuum of MgO Single Crystals and the Electric Field Effect

Experimental techniques are described and data are presented on bending creep of single-crystal MgO in vacuum from 800° to 1630°C. Evidence is discussed which supports the conclusion that creep near 1000°C is rate-controlled by cross-slip of screw dislocations with an activation energy of 1.5±0.25 eV. Creep above 1300°C takes place at a constant rate with an activation energy of 5.85±0.73 eV and a stress dependence exponent of 3. This creep is attributed to oxygen-ion diffusion-controlled climb of edge dislocations. The effect of an electric field to give a transient acceleration of the creep rate is described. Experiments to define and characterize this effect are described and discussed.