Activities
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Seminars
| Seminar on Theoretical and Computational Physics:
| | Title | Novel Thermoelectrics – Role of Nanostructures
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| Speaker | Prof. S. D. Mahanti
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| Affiliation | Michigan State University, USA
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| Date | Wednesday, 25-07-2007
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| Time | 10h00
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| Location | Meeting Room 1st floor, Institute of Physics and Electronics, 10 Đào Tấn, Ba Đình, Hà Nội
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| Abstract | During the last several years, there has been a renewal of great interest in discovering/synthesizing novel thermoelectric materials with high efficiency, driven by the need for direct conversion of heat to electricity. The efficiency of a thermoelectric device at the operating temperature T is determined, among other things, by the ZT factor called the figure of merit (FOM). ZT = S^2σT/κ_tot, where S is the Seebeck coefficient, σ is the electrical conductivity, and κtot is the total thermal conductivity from phonons and electrons. For many years the maximum values of ZT were hovering around 1. Significant improvements in ZT values have been seen recently in a large class of materials both at room and higher temperatures. Physical reasons for this improvement involve some sort of nano-scale physics. For example, nanoscale inhomogeneities scatter phonons efficiently to reduce lattice thermal conductivity (beyond what is known as the alloy limit) without degrading the electronic transport properties (hence enhance ZT). Nano-structure and defect induced changes in the electronic structure near the chemical potential can increase S without diminishing σ significantly resulting in an increase in the power factor S^2σ and ZT. In this paper, we will discuss three examples where nano-scale physics appears to be important; Bi_2Te_3-Sb_2Te_3 superlattices, PbTe-PbTeSe quantum dot systems, and bulk AgSbPb_mTe_m+2 (LAST-m), focusing a bit more on LAST-m.
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