Specific features of heat transfer in the orientationally ordered phases of molecular crystals in the region with predominant phonon-phonon scattering

Thermal conductivity of an orientationally ordered tert-butanol crystal was measured in the temperature range T = 4–150 K at equilibrium vapor pressure. The literature data on the thermal conductivity of a number of orientationally ordered molecular crystals in the high temperature region were analyzed. It was shown that the thermal conductivity can be described as a sum of two contributions: due to propagating phonons and localized “diffuse” modes. Generally, the contribution of localized “diffuse” modes is inversely proportional to the number of molecules Z in the unit cell and temperature independent. It is suggested that strong hybridization of acoustic phonons and low-frequency optical phonon excitations in ordered crystals is the main factor influencing the heat transfer in a molecular crystal.