Kinetics of Plastic Deformation in CuBr Single Crystals at Low Temperatures

Single crystals of CuBr with zincblende structure, deformed in compression at a strain rate 2×10^-4 s^-1 between room and liquid-nitrogen temperatures, exhibit two well-defined regions in the critical resolved shear stress (CRSS) versus temperature relationship. At rather low temperatures in the range from 78 to 150 K, the slope d ln /dT of the straight line fitted to the data points plotted in log-linear coordinates is found to be 2.9 times greater than that at temperatures between 150 and 300 K. Similar behaviour is also observed in the case of temperature dependence of activation volume associated with the CRSS. Data analysis in terms of the kink-pair nucleation model of plastic flow shows that stress-assisted thermally-activated escape of screw dislocations trapped in Peierls troughs induces slip below about 150 K. At temperatures above 150 K, CRSS is determined by the unpinning of edge-dislocation segments from groups of randomly dispersed point defects, e.g. residual gaseous and metallic impurities, deformation-induced defects formed during the pre-yield stage etc.