Avoided crossing of rattler modes in thermoelectric materials

Mogens Christensen, Asger Bech Abrahamsen, Niels Bech Christensen, Fanny Juranyi, Niels Hessel Andersen, Kim Lefmann, Jakob Andreasson, Christian Robert Haffenden Bahl, Bo B. Iversen

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    Engineering of materials with specific physical properties has recently focused on the effect of nano-sized 'guest domains' in a 'host matrix' that enable tuning of electrical, mechanical, photo-optical or thermal properties. A low thermal conductivity is a prerequisite for obtaining effective thermoelectric materials, and the challenge is to limit the conduction of heat by phonons, without simultaneously reducing the charge transport. This is named the 'phonon glass-electron crystal' concept and may be realized in host-guest systems. The guest entities are believed to have independent oscillations, so-called rattler modes, which scatter the acoustic phonons and reduce the thermal conductivity. We have investigated the phonon dispersion relation in the phonon glass-electron crystal material Ba8Ga16Ge30 using neutron triple-axis spectroscopy. The results disclose unambiguously the theoretically predicted avoided crossing of the rattler modes and the acoustic-phonon branches. The observed phonon lifetimes are longer than expected, and a new explanation for the low k(L) is provided.
    Original languageEnglish
    JournalNature Materials
    Issue number10
    Pages (from-to)811-815
    Publication statusPublished - 2008

    Cite this

    Christensen, M., Abrahamsen, A. B., Christensen, N. B., Juranyi, F., Andersen, N. H., Lefmann, K., Andreasson, J., Bahl, C. R. H., & Iversen, B. B. (2008). Avoided crossing of rattler modes in thermoelectric materials. Nature Materials, 7(10), 811-815. https://doi.org/10.1038/nmat2273