An Integrated Approach to Thermoelectrics: Combining Phonon Dynamics, Nanoengineering, Novel Materials Development, Module Fabrication, and Metrology

This review discusses the longstanding efforts to develop advanced thermoelectrics through a multidisciplinary approach by combining condensed matter physics, nanotechnology, solid-state chemistry, electrical engineering, mechanical engineering, and metrology. The phonon dynamics of skutterudites, clathrates, tetrahedrites, and layered LaOBiSSe are investigated through inelastic neutron scattering, allowing insights into their low lattice thermal conductivity due to rattling in a cage as well as under planar coordination. The electrical resistivity, Seebeck coefficient, and Hall coefficient of Bi-nanowires are successfully measured with a home-made system, demonstrating a size effect in thermoelectric and galvanomagnetic phenomena. For PbTe-based bulk thermoelectrics, an exceptionally high figure of merit ZT (approximate to 1.8 at 800 K) is achieved through nanostructuring. Moreover, correspondingly high conversion efficiency (approximate to 11% for a temperature difference of 590 K) is demonstrated in nanostructured PbTe-based modules. Sulfides (tetrahedrite, colusite, and CdI2-type layered systems) and arsenides (LnFeAsO and BaZn2As2) are developed as environmentally friendly and emerging thermoelectric materials, respectively. The output power and efficiency of modules with novel materials, including nanostructured PbTe, Zn4Sb3, and clathrates, are measured with the highly accurate self-made system. Future opportunities and challenges for the widespread use of thermoelectric waste heat recovery and energy harvesting are also discussed.