Abstract:
A detailed understanding of atomic dynamics (phonons) is of broad interest for the design of efficient energy materials, for example to establish reliable microscopic models of thermal transport and thermodynamics. Lattice instabilities are deeply connected to atomic vibrations and impact functional properties in many materials, including ferroelectrics, thermoelectrics, phase-change materials, and superionic conductors.
Neutron and X-ray scattering and optical spectroscopy measurements can map phonon dispersions throughout reciprocal space, providing a quantitative information on the mean-free-paths of heat-carrying vibration modes, and revealing dominant scattering mechanisms, including anharmonicity, electron-phonon coupling, and scattering by defects or nanostructures. Such microscopic information about the microscopic origins of thermal transport provides important insights to design more efficient thermoelectric materials, for example. In addition, first-principles simulations of the atomic dynamics enable the rationalization of extensive experimental datasets. In particular, ab-initio molecular dynamics simulations at finite-temperature allow us to capture striking effects of anharmonicity near lattice instabilities.
In this presentation, I will present results from our recent investigations of phonon transport in several important thermoelectric materials (PbTe, SnTe, AgSbTe2, SnSe, Mo3Sb7, tetrahedrites) [1-6]. Further, phonons can provide a large contribution to the entropy of solid-solid phase-transitions, and I will discuss several cases where our investigations of anharmonic phonons lead to a better understanding of phase-stability, highlighting recent results on thermodynamics of the metal-insulator transition in VO2 [7] and in ferroelectric perovskites.
Website: https://delaire.pratt.duke.edu/

Bio:
Olivier Delaire obtained his PhD from Caltech in 2006. His doctoral thesis investigated the role of phonons and electron-phonon coupling on the entropy of crystalline solids, primarily in superconducting transition metal compounds (Louis Rosen prize for best PhD thesis at the Los Alamos Neutron Science Center). After holding postdoc and research staff positions at Caltech, he became a Clifford Shull fellow in the Neutron Sciences Directorate at Oak Ridge National Laboratory (2008). As a research staff in the Materials Science and Technology Division at ORNL and as co-PI on the S3TEC Energy Frontier Research Center, he initiated a program to investigate phonons in thermoelectric materials with neutron and x-ray scattering, supporting several postdocs (Drs Jie Ma, Chen Li, Jiawang Hong, Jen Niedziela, Dipanshu Bansal). He also led an ORNL-LDRD project to develop software to model inelastic scattering data from first-principles simulations. He received a DOE Early Career Award grant (2014). Since 2016, Olivier Delaire is a Professor at Duke University. http://mems.duke.edu/faculty/olivier-delaire