Dispersions and lifetimes of low energy heat carrying phonons in the cage based materials Ba8Ge40.3Au5.25
In cage-based crystals, the guest-host interaction is widely accepted to be responsible for their exceptional low thermal conduction, opening new routes for the design of thermoelectric materials. We recently investigated the lattice dynamic of a Si-based [1] and Ge-based [2] clathrates and we demonstrated that the guest vibrations with the lowest energies act as a low pass filter for heat carrying phonons. A first step toward the understanding of the thermal conductivity in these materials would be to calculate the part of the conduction arising from the not filtered phonons. It requires the knowledge of their dispersions and lifetimes, a basic quantity, this latter, that is not accessible experimentally because of the finite sizes of the 4D instrumental resolution [1,2]. The high energy resolution setup of the IN5 cold TOF spectrometer offers an opportunity to overcome this limitation. Moreover, we grew a cubic centimeter single grain of the clathrate Ba8Ge40.3Au5.25 which has an exceptional crystalline quality (mosaïcity of 0.01°). In this proposal, we propose to map the dispersions of acoustic phonons at 300 K and 10 K in order to highlight the effect of the guest vibrations.
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PAILHES Stephane; DE BOISSIEU Marc; GIORDANO Valentina; LORY Pierre Francois and OLLIVIER Jacques. (2015). Dispersions and lifetimes of low energy heat carrying phonons in the cage based materials Ba8Ge40.3Au5.25. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.7-01-409
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