Anomalies of internal friction in CsI single crystal at liquid helium temperatures caused by plastic deformation

Acoustic relaxation in undeformed and plastically deformed CsI single crystal has been studied using the composite oscillator technique at frequencies (1–7) × 10⁵ Hz in the temperature range 2–15 K. Plastic deformation leads to appearance of an internal friction peak localized in the temperature interval 4–5 K. It is shown that the peak shifts towards higher temperatures when increasing the vibration frequency and corresponds to a thermally activated relaxation process with very low values of the activation energyU ≈ 1.9×10⁻³ eV and the attack frequencyν ₀≈6.7 × 10³ s⁻¹. Interaction of sound with dislocation kinks migrating in the second order Peierls relief is considered as a possible mechanism of the peak. Research was made possible in part by Grants U9T000 and U9T200 from the International Science Foundation and supported in part by the Fundamental Research Foundation of Ukraine (Project 2.4/156 “Bion”).