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Abstract

Synthetic bulk and natural pyrite from the hydrothermal mine in Schonbrunn (Saxony, Germany) are confirmed to be stoichiometric FeS2 compounds and stable (for thermoelectric applications) up to similar to 600 K by combined thermal, chemical, spectroscopic and X-ray diffraction analyses. Natural pyrite with a small amount (<0.6 wt%) of well-defined transition metal carbonates revealed characteristics of a nondegenerate semiconductor and is suitable as a model system for the investigation of thermoelectric performance. In the temperature range 50-600 K both natural and synthetic high quality bulk FeS2 samples show electrical resistivity and Seebeck coefficients varying within 220-5 x 10(-3) omega m and 4 - (-450) mu V K-1, respectively. The large thermal conductivity (similar to 40 W m(-1) K-1 at 300 K) is exclusively due to phononic contribution, showing a well pronounced maximum centered at similar to 75 K for natural pyrite (grain size <= 5 mm). It becomes almost completely suppressed in the sintered bulk samples due to the increase of point defect concentration and additional scattering on the grain boundaries (grain size <= 100 mu m). The thermoelectric performance of pure pyrite with ZT similar to 10(-6) at 600 K is indeed by a factor of similar to 1000 worse than those reported earlier for some minerals and synthetic samples.