Phonon relaxation time due to impurities with internal degrees of freedom

Abstract

Application of thermodynamic Green's functions is made to the study of phonon scattering by impurities having two internal energy eigenstates over which transitions take place in the presence of lattice waves. The equation-of-motion method is used to solve the Green's functions. The inverse relaxation time for phonons is found to be essentially temperature dependent and is peaked at a frequency slightly different from the energy gap between the levels. The low-temperature thermal conductivity of Li-doped KCl is finally studied in the light of the present results. © 1976 The American Physical Society.