Thermally Activated Deformation of KCl and KCl-KBr Single Crystals at Low Temperatures between 1.8 and 70 K

The critical-resolved shear stress and the strain-rate dependence of flow stress for KCl pure crystals and KCl-1, 4, 22 and 48 mol% KBr solid-solution crystals were measured over a temperature range between 1.8 K and 70 K. The activation analyses of the results showed that an Arrhenius rate equation for plastic deformation appeared to hold above 15 K for KCl and KCl-1 and 4 mol% KBr and above 25 K for KCl-22 and 48 mol% KBr, but not below these temperatures. Such discrepancy of the Arrhenius rate equation has been interpreted by the fluctuation of activation enthalpy due to random distribution of solute atoms. In the present interpretation the pre-exponential factor of the Arrhenius rate equation should have a strong temperature-dependence, especially in the low-temperature range, which agrees well with experimental results.