Low-Temperature Acoustic and Thermal Properties of Plastically Deformed, High-Purity Polycrystalline Aluminum

The low‐temperature internal friction Q—1, thermal conductivity κ, specific heat cp and heat release of plastically deformed, high‐purity aluminum polycrystals have been investigated and have been compared with measurements on an amorphous SiO2 specimen. Plastic deformation has a pronounced effect on both internal friction Q—1 and thermal conductivity κ in the superconducting state. The magnitude of the internal friction Q—1 can be increased over two orders by plastic deformation over that observed on an annealed sample, and approaches a value approximately equal to that of the amorphous SiO2 specimen. The lattice thermal conductivity κ of the deformed specimens also has a magnitude which is of the same order as that of amorphous SiO2, it is, however, nearly independent of the amount of deformation. No “glass‐like” anomalies could be observed in the specific heat cp and heat release measurements. The specific heat cp approaches a T3‐relationship at the lowest temperatures investigated, and heat release experiments clearly show no long‐time energy relaxation effects. Thus, it must be concluded that the defects introduced into deformed aluminum cannot be described with the tunneling model which had been proposed to describe the low temperature elastic and thermal properties of amorphous solids and which is based on the assumption of a constant spectral density of tunneling states. The phonon scattering mechanism observed in the deformed aluminum is tentatively related to the interaction of phonons with geometrical kinks in dislocations.