A universal T² behavior of low temperature thermal conductivity of some simple molecular polycrystals

The low-temperature dependence of thermal conductivity coefficient of dielectric crystals on temperature spreads over a vast region, both in terms of the absolute value of the coefficient as well as its functional dependence on the temperature. However, we were able to notice a group of simple molecular polycrystals which show their thermal conductivity very close to each other. What is more, the similarity of the thermal conductivity of the polycrystals for many reasons resembles known and studied for over 30 years the universality observed for low-temperature thermal conductivity of amorphous solids. Here, utilizing already developed thermal conductivity models, we try to understand what phenomena could result in the similarity of the thermal conductivity of the polycrystals and therefore explain the finding. Provided that some other conditions are met at least each of three different phonon scattering mechanisms could lead to the similarity