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 τ c (T), of highly covalent crystals of α-Al 2 O 3 , 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 ΔH(τ) is calculated from the elastic interaction energy of a trapezoidal kink pair. The calculation predicts narrow and abrupt kink pairs. The activation energy ΔH(τ) obtained describes the experimental relation log τ 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.