Neutron Scattering Study of Anharmonic Phonon Dynamics in Thermoelectric Materials
| Date/Time: | Wednesday, 11 Mar 2015 from 4:10 pm to 5:00 pm |
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| Location: | Physics 0003 |
| Phone: | 515-294-5441 |
| Channel: | College of Liberal Arts and Sciences |
| Actions: | Download iCal/vCal | Email Reminder |
Knowledge on phonon anharmonicity is critical to understand many physical properties of the materials, such as structural stability and phase transition, thermal expansion, and lattice thermal transport, among many others. Inelastic scattering experiments were performed with time-of-flight and triple-axis neutron spectrometers and neutron diffractometers to study the temperature dependence of the anharmonic lattice dynamics in several thermoelectric materials, including SnTe, PbTe, SnSe, Cr2Sb, Cu2Se, Mo3Sb7, etc. Four-dimension neutron scattering dynamical structural factors, S(Q,E), including anharmonic effects are simulated with first-principles methods and compared with measurements. Anharmonic phonon dynamics arise from various mechanisms in these materials, such as phonon-phonon, phonon-electron, phonon-magnon, and phonon-defects interactions. As an example, the experiments on rock-salt telluride thermoelectric compounds show that, although SnTe is closer to the ferroelectric instability, phonon spectra in PbTe exhibit a more anharmonic character. This behavior is reproduced in first-principles calculations of the temperature-dependent phonon self-energy, revealing how the nesting of phonon dispersions induces prominent features in the self-energy, which account for the measured anomalous inelastic neutron scattering spectra and their temperature dependence. Such knowledge not only helps us understand the existing materials better but also provide valuable guidance in engineering better functional materials.
Dr. Chen W. Li
2012-2015 Materials Science and Technology Division, Oak Ridge National Laboratory, Postdoc
2005-2012 Department of Applied Physics and Materials Science, California Institute of Technology, PhD
2003-2005 Department of Physics and Department of Chemistry, University of British Columbia
1999-2003 Department of Physics, Peking University, BSc