Dislocation motion and plasticity in MgO single crystals

The dislocation dynamics in MgO single crystals containing some hundred ppm of aliovalant impurities is investigated by three experimental techniques: in-situ deformation experiments in the high-voltage electron microscope, stress pulse-etching experiments on individual dislocations, and macroscopic deformation experiments for determining the activation parameters of the plastic deformation. All the three methods point out that the interaction between dislocations and point obstacles is the dominating mechanism controlling the dislocation mobility. The obstacles may be characterized by a total free energy of activation at zero stress of about 3 eV. The in-situ experiments yield further details about the statistical and kinematical nature of this interaction, but they also show that at least three other mechanisms are active additionally: the Peierls stress, jog-dragging, and the long-range interaction between the dislocations. The three methods show generally a relatively fair consistency of the experimental results. The effective stress measured electron microscopically is, however, very high which cannot completely be understood at present.