Internal friction in KCl single crystals

Abstract

It is shown that line tension, phonon damping and charge-cloud interactions all contribute to amplitude-independent mechanical damping, while depinning and charge-cloud stretching both contribute to amplitude dependence. A theory is developed for the complete model, specifically recognizing that, following depinning, repinning does not occur later in the stress cycle. The ultrasonic composite oscillator technique is used to measure mechanical damping and phase angle in KCI single crystals doped with CaCl₂ (1·3 and 11·5 p.p.m.) at temperatures between 400 and 700°C. Thermodynamic parameters of pinning are determined and the model is shown to give an excellent description of the data as a function of temperature, impurity concentration and strain amplitude.