Through a novel integrative approach combining scattering experiments with first-principles simulations, our research provides critical insights into microscopic thermal transport. In particular, our phonon measurements and simulations in thermoelectric materials such as PbTe, SnTe, AgSbTe2, or SnSe reveal the atomic and electronic origins of the low thermal conductivity in these and other important thermoelectric materials.
For example, we discovered that in PbTe a strong anharmonic coupling exists
between the ferroelectric transverse-optic phonon mode and the heat-carrying acoustic modes, which amplifies phonon scattering rates and enhances thermoelectric efficiency. The strong coupling arises from the proximity to the lattice instability, and new materials could be designed based on this principle.
The regime of strong coupling of phonons, as observed in PbTe and other materials, is of also of fundamental scientific interest. The harmonic phonon theory is both elegant and convenient, but new physics arises from strong couplings between quasiparticles. We investigate the phonon scattering rates arising from these couplings by mapping the phonon linewidths throughout the Brillouin zone by performing inelastic neutron and x-ray scattering measurements on single-crystals, and we perform computer simulations and modeling of phonon scattering rates, often based on first-principles methods such as density functional theory and ab-initio molecular dynamics.
Bansal, D, Li, CW, Said, AH, Abernathy, DL, Yan, J, and Delaire, O. "Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb(7-x)Te(x)." Physical Review B - Condensed Matter and Materials Physics 92, no. 21 (2015).
Li, CW, Hong, J, May, AF, Bansal, D, Chi, S, Hong, T, Ehlers, G, and Delaire, O. "Orbitally driven giant phonon anharmonicity in SnSe." Nature Physics 11, no. 12 (2015): 1063-1069.
Ma, J, Delaire, O, May, AF, Carlton, CE, McGuire, MA, VanBebber, LH, Abernathy, DL, Ehlers, G, Hong, T, Huq, A et al. "Glass-like phonon scattering from a spontaneous nanostructure in AgSbTe2." Nature Nanotechnology 8, no. 6 (2013): 445-451.
Shiga, T, Shiomi, J, Ma, J, Delaire, O, Radzynski, T, Lusakowski, A, Esfarjani, K, and Chen, G. "Microscopic mechanism of low thermal conductivity in lead telluride." Physical Review B - Condensed Matter and Materials Physics 85, no. 15 (2012).
Delaire, O, Ma, J, Marty, K, May, AF, McGuire, MA, Du, MH, Singh, DJ, Podlesnyak, A, Ehlers, G, Lumsden, MD et al. "Giant anharmonic phonon scattering in PbTe." Nature Materials 10, no. 8 (2011): 614-619.