Dislocation mechanism of low-temperature acoustic relaxation in niobium
P. P. Pal’-Val’, V. D. Natsik, L. N. Pal’-Val’The influence of the concentration of impurities, orientation, cooldown rate, and initial plastic deformation on acoustic relaxation in single-crystal and polycrystalline samples of normal and superconducting niobium is investigated in the temperature interval 2–12 K. On the basis of an analysis of existing experimental data, it is hypothesized for the first time that the microscopic mechanism of acoustic relaxation in niobium at helium temperatures is the thermally activated motion of screw dislocation jogs in the ⟨111⟩{011} slip system through Peierls potential barriers of the second kind. A relaxation theory is proposed, based on the model of resonance interaction of sound with chains of dislocation jogs formed on screw dislocations under the influence of thermoelastic stresses during rapid cooldown of the sample. A comparison of the results of the theory and experimental data are used to estimate the density of jogs and to find the height of the Peierls barriers of the second kind and the variation of the barrier height in the superconducting transition.