Anharmonic motions of Kr in the clathrate hydrate

Abstract

The anomalous glass-like thermal conductivity of crystalline clathrates has been suggested to be the result of the scattering of thermal phonons of the framework by 'rattling' motions of the guests in the clathrate cages. Using the site-specific (83)Kr nuclear resonant inelastic scattering spectroscopy in combination with conventional incoherent inelastic neutron scattering and molecular-dynamics simulations, we provide unambiguous evidence and characterization of the effects on these guest-host interactions in a structure-II Kr clathrate hydrate. The resonant scattering of phonons led to unprecedented large anharmonic motions of the guest atoms. The anharmonic interaction underlies the anomalous thermal transport in this system. Clathrates are prototypical models for a class of crystalline framework materials with glass-like thermal conductivity. The explanation of the unusual molecular dynamics has a wide implication for the understanding of the thermal properties of disordered solids and structural glasses.

Vibrational dynamics of the host framework in Sn clathrates

“…Kr 27,28 , respectively -were targeted. On the other hand, NRIXS studies on skutterudites (a related class of thermoelectric materials) helped elucidate the contribution of the host framework, in addition to that of the filler, to the lattice thermal conductivity in a series of experiments probing different (Fe, Sb) sites 29,30 .…”

Condensed Matter Physics Using Nuclear Resonant Scattering

“…The measurement of the PDOS under high pressures using a diamond anvil cell (DAC), where the sample size is typically less than 1 mm 2 , has been performed to study the core of the earth. [106][107][108] In addition, many important studies using the features of nuclear resonant inelastic scattering spectroscopy have been performed, e.g., on nanoparticles, [109][110][111][112][113][114] thin films, [115][116][117][118][119][120][121] quasi crystals, 122) clathrates, 123,124) superconductors, [125][126][127][128] filled skutterudites, [129][130][131][132] and glass. 133,134) The nuclear resonance scattering method can be applied to not only solids but also liquids.…”

Les clathrates hydrates

“…Vers la fin des années 80, deux hypothèses ont été émises quant à l'origine de ce comportement inhabituel : la taille des mailles élémentaires limitant le libre parcours moyen des phonons [37] ou un couplage entre modes de basse fréquence des sous-structures hôte et invitée influençant la diffusion des phonons [38]. Récemment, cette dernière hypothèse a été vérifiée par une série d'analyses expérimentales et théoriques [39]. Des calculs théoriques de dynamique de réseau ont mis en évidence un croisement évité entre les branches acoustiques du clathrate hydrate et les modes « rattling » des molécules incluses [40,41], comme illustré par les courbes de dispersion des phonons du clathrate hydrate de xénon (Figure 8).…”