Effect of plastic deformation on the shape and parameters of the low-temperature peak of internal friction in niobium

Abstract

Temperature dependences of the decrement of longitudinal vibrations are studied at moderately low temperatures in polycrystalline niobium with the residual resistivity ratio RRR=60 at frequencies 78 and 363 kHz. A peak of internal friction is detected in the vicinity of 200 K. The height, width, and temperature of the peak change significantly upon a variation of vibrational frequency and as a result of changes in the defect structure of the sample under thermocycling, plastic deformation, or prolonged low-temperature recovery. It is shown that the absorption peak is due to the interaction of elastic vibrations of the sample with a system of identical thermally activated relaxators with an activation energy of 0.15 eV and an attack frequency of 1×1010 s−1 in a nearly perfect crystal. A theory is proposed for describing the variation of the shape and parameters of the internal friction peak due to statistical dispersion of the values of activation energy of the relaxators.