Thermal conductivities of a clathrate with and without guest molecules.

Abstract

The thermal conductivities of Dianin's compd. [4-(p-hydroxyphenyl)-2,2,4-trimethylchroman] and its ethanol adduct in the temp. range 20-250 K are reported. This clathrate has the same stable structure both with and without guest mols. in its hourglass-shaped cages, thereby allowing the first direct exptl. investigation of the effect of a clathrate's guest species on the thermal cond. Both with and without the guest mols., the thermal cond. is similar to that of a glass, and the presence of the guest mol. enhances the resistance to heat flow. The thermal cond. is described in terms of umkalpp-, 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 assocd. with the motion of the Me groups of the Dianin mol. for the unresolved host lattice, and the motions of host Me groups and the motions of the ethanol guest mols. within the cages for the ethanol adduct of Dianin's compd.