Thermal conductivities of a clathrate with and without guest molecules

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Abstract
The thermal conductivities of Dianin’s compound [4-(p-hydroxyphenyl)-2,2,4-trimethylchroman] and its ethanol adduct in the temperature range from 20 to 250 K are reported. This clathrate has the same stable structure both with and without guest molecules in its hourglass-shaped cages, thereby allowing the first direct experimental investigation of the effect of a clathrate’s guest species on the thermal conductivity. Both with Iand withoutR the guest molecules, the thermal conductivity is similar to that of a glass, and the presence of the guest molecule enhances the resistance to heat flow. The thermal conductivity is described in terms of umklapp-, boundary-, and resonant-scattering resistance contributions. The latter is ascribed to the interaction of localized modes with the acoustic modes of the host lattice. It is proposed that the localized modes are associated with the motion of the methyl groups of the Dianin molecule for the unsolved host lattice, and the motions of host methyl groups and the motions of the ethanol guest molecules within the cages for the ethanol adduct of Dianin’s compound.