The internal friction of plastically deformed high-purity monocrystalline, and impure polycrystalline, specimens was measured at 0.065 to 2K. It was found that plastic deformation had a marked effect upon the internal friction of high-purity monocrystalline specimens, and that this effect was almost independent of temperature. However, the internal friction of the impure polycrystalline specimens was almost independent of the extent of plastic deformation. A comparison of the experimental results with various models for the dynamic scattering of acoustic phonons by dislocations led to the conclusion that the results could not be explained by a 2-level tunnelling model. It was instead suggested that a strong interaction between acoustic phonons and geometrical kinks in non-screw dislocations was responsible for the observed internal friction.

Low-Temperature Internal Friction in High-Purity Monocrystalline and Impure Polycrystalline Niobium after Plastic Deformation. W.Wasserbäch, E.Thompson: Physica Status Solidi A, 2001, 184[2], 381-402