Disorder effects on heat transport properties of orientationally disordered crystals

Abstract

The thermal conductivity $\ensuremath{\kappa}(T)$ of the orientational glass state of 1,2-difluoro-1,1,2,2-tetrachloroethane (${\text{CFCl}}_{2}{\text{-CFCl}}_{2}$, Freon 112) and cyanocyclohexane $({\text{C}}_{6}{\text{H}}_{11}\text{CN})$ has been measured under equilibrium pressure within the temperature range 2--100 K. The results show that the soft-potential model is able to account for low-temperature data and, indeed, quantitative agreement of all data considered is found within this realm. The details beyond such temperatures are heavily dependent on chemical details and a large plateau is observed for Freon 112 which is rationalized in terms of resonant scattering of phonons by simple oscillators. Such a view is given additional support by the presence of a strong low-frequency feature in the generalized frequency spectrum of the former material as proven by inelastic neutron-scattering spectroscopy.