With increasing demand in world's energy market and enormous green house gas emission, thermoelectric (TE) materials have become a hot research topic in condensed mater physics and energy-related materials science, since they can directly generate electricity when temperature gradient is applied, which indicates the potential use for waste heat recovery. A good TE material should have low thermal conductivity, low electrical resistivity and high Seebeck coefficient. However, the above parameters are coupled inherently and it is difficult to optimize one parameter without having negative effects on another. Furthermore, the large scale application of TE materials is limited by the low cost/efficiency ratio due to the component expensive/toxic elements and complex synthesis processes. In this work, a new compound Cu12Sb4S13 tetrahedrite with predicted intrinsic low thermal conductivity is synthesized and characterized systematically for its thermoelectric properties. The origin of intrinsic low thermal conductivity is investigated by both theoretical and experimental work. The effects of foreign atom substitution on TE properties of tetrahedrite are studied with the conclusion that TE properties of this compound are not as sensitive to impurities as is typically the case for TE materials. In addition, band structure engineering is performed on tetrahedrite by Ni and Zn co-doping and Se substitution. Nickel substitution introduces new energy levels near the Fermi level, Zn plays the role or raising the Fermi level to the top of valence band, optimizing electrical transport properties for TE application. Selenium substitution in tetrahedrite decouples the three inter-dependent parameters determining TE behavior by increasing band degeneracy near the Fermi level. Finally, a rapid and economic method which directly uses natural mineral itself is developed for synthesizing tetrahedrite based TE materials. By high energy mixing of tetrahedrite natural mineral powder and pure elemental powders, TE materials with high performance can be produced in large quantities in a very short time. Overall, we identify a new family of compounds based on a natural mineral as high performance TE materials with intrinsically low thermal conductivity. Our new method of directly using natural mineral in TE material synthesis demonstrates a new route to large scale thermoelectric applications.
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