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, T_c, 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 T_c 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.

Keywords:

• Dislocation
• ultrasonic oscillatory stress
• activation energy
• monovalent ion
• isotropic strain

Acknowledgements

We would like to thank S. Yamaguchi, M. Azuma, H. Teraji, E. Ogawa and Y. Yamanaka for their experimental assistance.