Horbatenko Y. Thermal conductivity of molecular crystals formed by flexible molecules

The thesis is devoted to the study of thermal conductivity of dielectric molecular crystals formed by flexible molecules. The thermal conductivity investigations have been carried out using the stationary steady-state heat flux method in wide temperature range beginning from liquid helium one. The temperature dependences of thermal conductivity of orientationally-ordered and orientationally-disordered molecular crystals have been experimentally obtained. It has been found that thermal conductivity of investigated molecular crystals in both ordered and disordered states, in the region of predominance of phonon-phonon scattering processes, can be represented as the sum of three contributions – phonon, diffuse and thermoactivation. It has been found that the diffuse contribution in thermal conductivity of a polymorphic crystal, which is determined by the number of optical modes, depends inversely on the number of molecules in the unit cell. Thermally-activated term appears both in orientational-ordered and orientational-disordered crystals and it`s value depends linearly on the molecule activation energy; analogous dependence was obtain for quasicrystals.