# CMT Seminar: Thermoelectrics: Applications, Materials Optimization, and Metrology

Monday, July 11, 2011 – 3:15pm – 4:30pm

Reiss 502

Joshua Martin

NIST

Thermoelectric effects enable the inter-conversion of thermal and electrical energy and are the physical mechanisms for power generation (waste heat recovery) and solid-state refrigeration applications. The dimensionless figure of merit, ZT = S2σT/κ, defines the effectiveness of TE materials, where S is the Seebeck coefficient, σ the electrical conductivity, T the absolute temperature, and κ the total thermal conductivity. Optimizing these interdependent physical parameters to achieve acceptable efficiencies (where ZT > 1) requires materials exhibiting a unique combination of properties. Several approaches have been developed to identify these potential thermoelectric materials, including the phonon-glass electron-crystal concept (PGEC). Recent progress can be attributed to nanoscale enhancement due to the phenomenological properties of nanometer length scales, including quantum confinement effects, enhanced phonon scattering, and charge carrier filtering. To understand the structure-property relationships and to fully evaluate the potential performance of these new thermoelectric materials requires a thorough characterization of their electrical and thermal transport properties. The Seebeck coefficient is one physical property that singularly identifies a material’s potential usefulness for thermoelectric application, as it is highly sensitive to the electronic structure. However, researchers employ a variety of measurement techniques, conditions, and probe arrangements. This diversity often results in conflicting materials data, further complicating the inter-laboratory confirmation of reported higher efficiency thermoelectric materials. In an effort to identify optimal thermoelectric measurement protocols, we have developed a complimentary strategy to both evaluate and compare these different probe arrangements and measurement methodologies: first, through the design of an improved experimental apparatus, and second, through computational Seebeck coefficient metrology simulations using finite element analysis. This talk will include a general overview of thermoelectric effects, applications, and methods of optimization, with a focus on our methods to develop optimal thermoelectric metrology protocols and standards.

Host: Jim Freericks