Interactions of dislocations with impurity atoms of different valencies and the high-frequency internal friction in superconducting and normal lead. I. The amplitude-dependent internal friction and its analysis
Abstract
To find out the role of the electrostatic interaction of dislocations with impurity atoms in Pb, we have investigated the amplitude dependence of the high-frequency internal friction at 4.2 °K. Lead was doped with Tl, Sn, Bi, Cd, or Sb to a level of 8 · 10−3 at. %. The critical amplitude ϵ0c., i.e., the amplitude at which the friction becomes amplitude dependent, was found to increase in going from Tl to Sb. As the samples went over from the s into the n state, ϵ0c increased by 30–40%. Analysis of the amplitude dependences within the framework of the Granato-Lücke athermal theory enabled us to obtain values for the characteristic stress level, Γ, for dislocation detachment from the impurities in question. The Γ values changed at the n–s transition by about 30%. A method is developed for the analysis of experimental data with the object of determining the contributions of different physical natures to the total energy of interaction of a dislocation wtih an impurity atom, and quantitative information about these contributions has been obtained. An analytical comparision between the theoretical results and the experimental data is carried out. The causes of the influence of the n-s transition on the dislocation-unpinning process are discussed. It is concluded that the electronic viscosity has a significant effect on the amplitude-dependent, dislocation-induced losses. The results of a theoretical consideration of this problem are presented.