Overview of Various Strategies and Promising New Bulk Materials for Potential Thermoelectric Applications
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Overview of Various Strategies and Promising New Bulk Materials for Potential Thermoelectric Applications Terry M. Tritt Department of Physics & Astronomy Clemson University, Clemson, SC, USA Abstract Recently, there has been a renewed interest in thermoelectric material research. There are a number of different systems of potential thermoelectric (TE) materials that are under investigation by various research groups. Some of these research efforts focus on minimizing lattice thermal conductivity while other efforts focus on materials that exhibit large power factors. An overview of some of the requirements and strategies for the investigation and optimization of a new system of materials for potential thermoelectric applications will be discussed. Some of the newer concepts such as low-dimensional systems and Slack’s phononglass, electron-crystal concept will be discussed. Current strategies for minimizing lattice thermal conductivity and also minimum requirements for thermopower will be presented. The emphasis of this paper will be to identify some of the more recent promising bulk materials and discuss the challenges and issues related to each. This paper is targeted more at “newcomers” to the field and does not discuss some of the very interesting results that are being reported in the thin film and superlattice materials. Some of the bulk materials which will be discussed include complex chalcogenides (e.g.CsBi4Te6 and pentatellurides such as the Zr1-XHfXTe5 system), halfHeusler alloys (e.g. TiNiSn1-XSbX), ceramic oxides (NaCo4O2), skutterudites (e.g. YbXCo4-XSb12 or EuXCo4-XSb12) and clathrates (e.g. Sr8Ga16Ge30). Each of these systems is distinctly different yet each exhibits some prospect as a potential thermoelectric material. Results will be presented and discussed on each system of materials. Background On Thermoelectric Materials: Over the past five to six years there has been a heightened interest in the field of thermoelectrics driven by the need for more efficient materials for electronic refrigeration and power generation. [1, 2, 3] Proposed industrial and military applications of thermoelectric (TE) materials are generating increased activity in this field by demanding higher performance, nearroom-temperature TE materials than presently exist. Thermoelectric refrigeration is an environmentally “green” method of small-scale localized cooling in computers, infrared detectors, electronics and many other applications. Recent utilization of Peltier coolers in relation to refrigeration of biological specimens and samples is an emerging application of thermoelectrics. Power generation applications are currently being investigated by the automotive industry as a means to develop electrical power from waste engine heat and, of course, the deep space applications are well established. Given the recent energy needs experienced in the United States there is even a more pressing need to investigate alternative energy conversion technologies in this country, eg. the thermal to electrical energy conversion from na
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