Olivier Delaire (Oak Ridge National Laboratory)
Improving our microscopic understanding of heat transport is critical to design energy materials and devices reaching higher efficiencies, in particular for thermoelectric applications. Thus, establishing a complete picture of phonon dispersions and mean-free-paths is crucial to obtaining a realistic microscopic characterization of thermal conductivity, against which theories of phonon transport can be tested. Thanks to recent advances in experimental facilities, combined with developments in data modeling, inelastic neutron scattering can now be used to map phonon excitations across the entire volume of the Brillouin zone. Our neutron scattering measurements of phonons in single-crystals directly probe features in phonon dispersions and lifetimes that are associated with a rich variety of scattering mechanisms, including: phonon anharmonicity, electron-phonon coupling, and scattering by point-defects or nanostructures. These different processes may be combined to increase phonon scattering rates, and improve thermoelectric efficiency, for example. Our neutron scattering investigations are also complemented with synchrotron x-ray scattering experiments of the structure and dynamics. In addition, we leverage first-principles simulations of atomic dynamics, including effects of anharmonicity and defects, to extract key scientific insights from large experimental datasets. We present results from several studies of important thermoelectric materials [1,2], illustrating how this integrated approach, combining scattering experiments and computational modeling, was used to obtain a new level of microscopic understanding of thermal conductivity in advanced materials. Our results suggest avenues to improve the performance of thermoelectric materials.
[1] O. Delaire, J. Ma, K. Marty, A. F. May, M. A. McGuire, M.-H. Du, D. J. Singh, A. Podlesnyak, G. Ehlers, M. Lumsden, B. C. Sales, ³Giant Anharmonic Phonon Scattering in PbTe², Nature Materials 10, 614 (2011).
[2] J. Ma*, O. Delaire*, A. F. May, C. E. Carlton, M. A. McGuire, L. H. VanBebber, D. L. Abernathy, G. Ehlers, Tao Hong, A. Huq, Wei Tian, V. M. Keppens, Y. Shao-Horn, and B. C. Sales, ³Glass-like phonon scattering from spontaneous nanostructure in AgSbTe2², Nature Nanotechnology 8, 445 (2013).
We acknowledge funding from the US Department of Energy, Office of Basic Energy Sciences, Materials Science and Engineering Division, and through the S3TEC Energy Frontier Research Center.
