Tunnel modes and kinetic properties of glasses at low and high temperatures

A theoretical approach is presented intending to unify tunnel mode and structural defect concepts existing in the theory of amorphous solids. Origins of double-well potentials (dwp) are discussed and two types of dwps—soft and rigid—are emphasised. Soft dwps are mainly responsible for low-temperature properties whereas rigid dwps determine the properties of glasses at higher temperatures. Tunnelling in rigid dwps is largely influenced by the barrier fluctuative preparation, the multi-phonon processes are of importance at higher temperatures. The dwp relaxation time up to room temperature is analysed. The sound attenuation due to the relaxation and multi-phonon mechanisms is calculated and their relative contributions are compared. The role of these processes in the thermal conductivity and temperature plateau formation is discussed.