Relaxations in the Attenuation of Single Crystal Lead at Low Temperatures and Their Relation to Dislocation Theory

Abstract

Measurements of the attenuations of face-centered metals by Bordoni have shown attenuation peaks at low temperatures. By using the measurements of Bömmel on single crystal lead it can be verified that this is a relaxation and values can be obtained for activation energies and frequency terms. It is shown that the measured results correlate well with a relaxation due to the displacement of a dislocation from one atomic line to an adjacent one against the limiting shearing stress of the crystal. The limiting shearing stress measured for four face-centered metals is in good agreement with theoretical calculations of Cottrell. A higher temperature loss is also measured which increases exponentially with the temperature. It is shown that this term is due to breakaway of the dislocation from its impurity pinning points due to thermal agitation. This breakaway abstracts energy from the vibration and produces a loss independent of the frequency but increasing with temperature since more breakaways occur at higher temperatures. The activation energy of breakaways correlates well with the binding energy of impurity atoms.