Thermal resistivity due to three-phonon normal processes

Using the nonlinearized (space-dependent) Boltzmann transport equation, the effect of three-phonon normal processes on the thermal conductivity of solids has been studied. The heat energy density in a region of the system is regarded as the measure of the local temperature. This temperature is shown to be not necessarily independent of the position coordinates in the presence of normal processes. Consequently, the thermal resistivity due to these processes is in general finite and vanishes only in specialised cases.