Low-temperature α peak of the internal friction in niobium and its relation to the relaxation of kinks in dislocations

The influence of impurities on the parameters of the α peak of the internal friction in single-crystal and polycrystalline niobium is investigated; the internal friction is recorded in the temperature range 200–250 K at a vibrational frequency of $≈80 kHz.$ It is found that increasing the purity of the samples leads to an increase of the peak location temperature and to an increase of its width and amplitude. The structural sensitivity of this peak was observed previously in a study of the influence on this peak of a preliminary plastic deformation, thermocycling, and low-temperature recovery. A statistical description of the whole set of experimental data is proposed, which takes into account the dependence of the activation energy and attempt period on the impurity concentration and on the characteristic value and statistical scatter of the internal stresses. A new algorithm is developed for analyzing the experimental data to obtain empirical estimates for the values of the activation energy, its variance, the attempt period, and relaxation strength for the different structural states of the samples. It is shown that the α peak is a consequence of the resonant interaction of elastic vibrations with the thermally activated nucleation of kink pairs on dislocation segments lying in the valleys of the Peierls potential relief. Empirical estimates are obtained for the values of the main parameters characterizing this process. It is found that the properties of the α peak in niobium are in qualitative agreement with Engelke’s theory of the nucleation and relaxation of dislocation kinks.