Dislocation structure during creep of MgO single crystals

The dislocation substructure generated during compressive creep of MgO single crystals has been investigated using both etch-pit and transmission electron microscopy techniques. The type of dislocation substructure is dependent on strain. During transient creep nearly parallel cell walls are found whereas in steady state creep a nearly equiaxed network of cells is built up. Measurements of the density ρ of dislocations not associated with cell walls and of the cell wall area per volume S v reveal the following trends: During primary creep both ρ and S v are functions of strain; ρ decreases while S v increases with increasing strain. During steady state creep ρ and S v are constant. The isothermal stress dependence of the steady state values of ρ and S v can be described by relations ρ ∼ σ1·4, and SV∼σ0·7.