Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi6-x. - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Physical Review B: Condensed Matter and Materials Physics (1998-2015) Année : 2012

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi6-x.

Résumé

One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present a combined neutron scattering and theoretical investigation of the lattice dynamics in the type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe a strong hybridization between phonons of the Ba guest atoms and acoustic phonons of the Ge-Ni host structure over a wide region of the Brillouin zone, which is in contrast with the frequently adopted picture of isolated Ba atoms in Ge-Ni host cages. It occurs without a strong decrease of the acoustic phonon lifetime, which contradicts the usual assumption of strong anharmonic phonon-phonon scattering processes. Within the framework of ab initio density-functional theory calculations we interpret these hybridizations as a series of anticrossings which act as a low-pass filter, preventing the propagation of acoustic phonons. To highlight the effect of such a phononic low-pass filter on the thermal transport, we compute the contribution of acoustic phonons to the thermal conductivity of Ba8Ge40Ni6 and compare it to those of pure Ge and a Ge-46 empty-cage model system.

Domaines

Matériaux

Dates et versions

hal-00794211 , version 1 (25-02-2013)

Identifiants

Citer

H. Euchner, S. Pailhes, L.T.K. Nguyen, W. Assmus, F. Ritter, et al.. Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi6-x.. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2012, 86 (22), ⟨10.1103/PhysRevB.86.224303⟩. ⟨hal-00794211⟩
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