Thermal transport in dynamically disordered phases of molecular crystals: A thermo activation mechanism

Isochoric thermal conductivity of crystalline 1,1-difluoroethane (F-152a freon) is measured on samples of different densities in the dynamically orientationally disordered (DOD) phase. The thermal conductivity increased with temperature, similar to how it occurs in amorphous and glass-like substances above the plateau area. It is found that this behavior can be described by a thermo-activation mechanism with constant activation energy and density-dependent pre-exponential factor. Bridgman coefficient g = - ( partial differential ln kappa/ partial differential lnV)T is 6.0 +/- 0.5. It is shown that the thermal conductivity of a number of other molecular crystals with the dynamic orientational disorder can be described in a similar way. Possible reasons for the thermal activation behavior of thermal conductivity are discussed.

Automated summary

The isochoric thermal conductivity of crystalline 1,1-difluoroethane (F-152a freon) was measured in the dynamically orientationally disordered (DOD) phase, showing an increase in thermal conductivity with temperature that can be described by a thermo-activation mechanism with constant activation energy and density-dependent pre-exponential factor. Bridgman coefficient was found to be 6.0 +/- 0.5. The study suggests that thermal conductivity of other molecular crystals with dynamic orientational disorder can be similarly described, and discusses possible reasons for this thermal activation behavior.