Heat transport in thermoelectrics

Yaguo Wang, Purdue University

Abstract

The overall objective of this research is to establish a fundamental understanding of heat transport dynamics in typical thermoelectric materials. The focus of this thesis is the study of guest-host interactions in mistch-metal filled antimony skutterudites and of phonon generation and dephasing process in Bi2Te3/Sb2Te3 superlattice. These tasks will be accomplished by using ultrafast time-resolved pump-probe experiments and molecular dynamics simulations (MD). Optical and acoustic phonon oscillations in Bi2Te3, Sb2Te3 and the Bi2Te3/Sb 2Te3 superlattice are excited by femtosecond laser pulses and detected with the ultrafast time-resolved pump-probe technique. The phonon scattering rates are extracted and compared in these materials, which confirms the existence of extra scattering channels within the hetero-structure of the superlattice. With a similar technique, the lattice vibrational properties in the mistch-metal filled antimony skutterudites as a function of the filling ratio is then analyzed. The measured resonant oscillation frequencies can be used to fit the lattice thermal conductivity and explain the reduced thermal conductivity in filled antimony skutterudites. Parallel MD programs have been developed to predict the overall lattice thermal conductivity of Bi2Te3—with & without coherent phonon generation and mode-wise lattice thermal conductivity for differentiating contribution from single phonon mode. MD programs are also used to understand non-thermal melting phenomenon in Bi2Te 3 as it is triggered by coherent phonon excitation. The ultimate goal of this research is to understand the heat transport process in thermoelectric materials both in macroscopic and microscopic views through constructing a complete picture of phonon dynamics in thermoelectrics and to then propose effective designs of high-performance thermoelectrics.

Degree

Ph.D.

Advisors

Xu, Purdue University.

Subject Area

Physics|Optics|Energy|Materials science

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