Thermoelectric materials, phenomena, and applications: A bird's eye view

High-efficiency thermoelectric (TE) materials are important for power-generation devices that are designed to convert waste heat into electrical energy They can also be used in solid-state refrigeration devices. The conversion of waste heat into electrical energy may play an important role in our current challenge to develop alternative energy technologies to reduce our dependence on fossil fuels and reduce greenhouse gas emissions. An overview of various TE phenomena and materials is provided in this issue of MRS Bulletin. Several of the current applications and key parameters are defined and discussed. Novel applications of TE materials include biothermal batteries to power heart pacemakers, enhanced performance of optoelectronics coupled with solid-state TE cooling, and power generation for deep-space probes via radioisotope TE generators. A number of different systems of potential TE materials are currently under investigation by various research groups around the world, and many of these materials are reviewed in the articles in this issue. These range from thin-film superlattice materials to large single-crystal or polycrystalline bulk materials, and from semiconductors and semimetals to ceramic oxides. The phonon-glass/electron-crystal approach to new TE materials is presented, along with the role of solid-state crystal chemistry. Research criteria for developing new materials are highlighted.