Strain-rate cycling tests associated with supersonic oscillation were carried out at 77－254K for four kinds of single crystals: KCl doped with Mg2+, Ca2+, Sr2+ or Ba2+ as a weak obstacles. It was found that the critical temperature, at which the effective stress is zero, increases when the divalent ionic size approaches increasingly that of the K+ ion.
moving dislocation
plastic deformation
strain-rate cycling tests
ultrasonic oscillation
force-distance profile between a dislocation and an impurity
critical temperature