Activation energy for dislocation breakaway from various monovalent ions in NaCl single crystals

Abstract

Combination method of strain-rate cycling tests and application of ultrasonic oscillations was carried out during plastic deformation of NaCl single crystals doped with Li+, K+, Rb+, Cs+ or F− at 77 K to room temperature. Relative curves between the stress decrement (Δτ) due to ultrasonic oscillatory stress and strain-rate sensitivity () of flow stress under superposition of the oscillation are obtained by the original method (strain-rate cycling test during the Blaha effect measurement) and have stair-like shapes for the specimens at low temperature. Assuming that the Cottrell–Bilby relation is suitable for the force distance between dislocation and the dopant ion, the values of G0, Tc, etc. are calculated from the data analysed in terms of Δτ vs. . G0 is the Gibbs free energy for overcoming of the dopant by dislocation at absolute zero and Tc the critical temperature at which the dopant does not act as obstacle to dislocation motion. The obtained energies G0 are found to be arranged linearly with the isotropic defect (Δε) around it in the each specimen.