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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.
