Thermal conductivities of a clathrate with and without guest molecules

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 and without 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.

Thermal conductivity of Xe clathrate hydrate at low temperatures

“…9 The degree of anharmonicity and coupling depends strongly on the type of guest molecule. 8 The glasslike behavior of the thermal conductivity also was detected in some doped semiconductors [10][11][12] and organic 13,14 clathrates. In this study the thermal conductivity of Xe clathrate hydrate has been investigated and the origin of the noncrystal-line behavior of the thermal conductivity of crystal hydrates discussed.…”

Crystal structure and thermal expansion of hexakis(phenylthio)benzene and its CBr4 clathrate

“…In HPTB systems the hydrogenbonded hexamer is replaced by a single host molecule with a permanent consolidated structure (15) (also vide iifra). The structures of HPTB and its inclusion compounds are of particular interest in light of the proposal that the unusual thermal conductivity observed for clathrate hydrates and Dianin's clathrate is ascribable to resonant scattering of acoustic modes by tlie localized optic modes brought about by an intrinsic motion of the nlolecular moieties (7,11). Examination of the thermal properties of the HPTB system will provide further information on the potential topological and (or) dynamical origin of the unusual thermal behaviour of clathrates.…”

“…We have initiated investigations of thermal properties of clathrates to get insight into the aforementioned aspects of molecular behaviour (5)(6)(7)(8)(9)(10)(11)(12). Thermal expansion is one of these properties.…”

Thermal Properties and Transition Behavior of Host-Guest Compounds Under High Pressure

“…The κ of single crystal and polycrystalline material of Dianin's compound, and its ethanol and CCl 4 clathrates was studied by White and co-workers [83,84,85]. They used both the hot-wire method and a steadystate radial heat flow method to study the behavior at high pressure [83], and a modulated heat flow method to study the behavior at atmospheric pressure [84,85,86].…”