INFLUENCE OF ELECTRONIC VISCOSITY AND IMP URITIES ON QUANTUM MOTION OF DISLOCATIONS OVER THE PEIERLS BARRIERS

The temperature dependences of yield stress and strain rate sensitivit y of deformation stress have been experimentally studied for a slip sy stem (100)[010] in pure single crystals beta-Sn over a temperature ran ge 0.5-4.4 K. The results obtained have supported the existence of the low temperature anomaly. This anomaly exhibits all the evidences of t he quantum process, i.e. the thermoactivated - to - athermal plastic f low transition at the temperature near and below 1 K. It is shown that the transition of the samples from the normal into the superconductin g state permits observation of the anomaly in a more wide temperature range. An effect of alloying of Sn with Cd on the anomaly has been als o investigated. It was found that a low-concentration impurity increas ed the threshold anomaly temperature whereas a high-concentration impu rity caused the athermal plastic flow to disappear. Leaning upon the f act that the Peierls barriers are the governing factors in a mobility of dislocations in the given slip system and upon the theoretical data on the quantum motion of dislocations in the Peierls relief [7,17,18] , a comprehensive theoretical analysis of the experimental findings ha s been made. Simple analytical expressions were obtained for the tempe rature dependences of plasticity properties in the quantum anomaly reg ion. A quantitative comparison between theoretical and experimental da ta has been made. The technique of calculating the empirical values of the main parameters of dislocation theory (Peierls stress, effective mass, linear tension and electron friction coefficient of dislocation string) has been developed and applied to a slip system (100)[010] in beta-Sn.