Deviations from Matthiessen's Rule Due to Phonon Spectrum Changes

The deviations from Matthiessen's rule which would be expected to result from changes in the phonon spectrum of a metal when chemical or physical defects are introduced, have been analyzed in greater detail within the framework of the Bloch-Gr\"uneisen theory. This work was prompted by certain contradictory statements appearing in the literature, and has led to a clarification of the situation regarding possible changes in the characteristic temperature θR. In addition, a fresh assessment of the applicability of this model to more recent experimental results is presented.