The additivity of the inverse of the relaxation times as assumed by Callaway is observed to be valid to lowest approximation; otherwise, interference terms like Mattheissen's deviation term should be considered. It is also observed that the phonon-scattering processes due to lattice defects and chemical impurities can be included in an approximation with the phonon boundary scattering to analyze the phonon conductivity results at low temperatures.

• Received 1 February 1979

DOI:https://doi.org/10.1103/PhysRevB.24.4493