Synthesis of selenium doted pyrite single crystals prepared by chemical vapor transport

Selenium is of environmental concern due to a possible exposure of 79Se radionuclide from a high-level nuclear waste repository to the biosphere or enlarged concentrations in soils and lakes or wetlands, threatening to health of vertebrates. Pyrite on the contrary is the most common iron sulfide on earth's surface and noted for the incorporation of trace elements into its structure. In this study, we report the development of a high temperature synthesis of pure selenium doted pyrite, using solid AlBr3, Fe0, S0 and Se0 by means of a chemical vapor transport reaction in a 2-zone furnace with a gradient of 700°C to 600°C in a two reaction step. The amount of 1.1wt% of homogeneously distributed selenium became incorporated into pyrite single-crystals with a size up to 0.5cm in diameter. X-ray absorption fine-structure investigations were performed for the determination of the valence state and structural bonding of incorporated Se into pyrite. These reveal the predominant incorporation of Se0 into pyrite structure without further bonding. This result indicates that the formation of a FeSxSey condensed matter, accompanied with a substitution of sulfur by selenium, is not likely. ► We performed a high temperature synthesis of Se doted pyrite by chemical vapor transport. ► The Se was homogenously distributed in pyrite single-crystals with a size up to 0.5cm. ► XAFS was used to determine valence state and structural bonding of incorporated Se into pyrite. ► Just zero-valent selenium could be detected into pyrite crystal structure. ► Only gaseous S and not Se reacted with Fe.