TEMPERATURE-DEPENDENCE OF THE PLASTIC-FLOW STRESS OF COVALENT CRYSTALS

A model is presented to explain the steep temperature dependence of the plastic flow stress tau(c)(T), of highly covalent crystals of alpha - Al2O3, Si and GaAs. The model assumes high and steep Peierls potentials: V-p(x)= Px(2) + Qx(n) (n > 2) for x < a/2, a being the period. The kink pair formation energy Delta H(iota) is calculated from the elastic interaction energy of a trapezoidal kink pair. The calculation predicts narrow and abrupt kink pairs. The activation energy Delta H(tau) obtained describes the experimental relation log tau(c) = A - BT with constants A and B. The results suggest that the kink pair formation is the rate controlling process of dislocation motion in covalent crystals.