Modelling nanoscale FeS₂ formation in sulfur rich conditions

The formation of single nanocrystals of the non-magnetic mineral iron pyrite (FeS₂) depends on the concentration of sulfur present during synthesis. In nature pyrite nanocrystals are often observed in sulfide-rich sediments, or during intracellular biomineralization in multicellular magnetotactic bacteria. However, characterizing these nanocrystals and understanding the formation processes in either of these sulfidic environments is challenging, as anisotropic crystal growth, alteration and dissolution are linked to the crystallographic orientation of surface facets, and in the latter case to the presence of water and microbial activity. In the present study we use a multi-scale thermodynamic model capable of describing the stability (formation) of nanocrystals as a function of size, shape, temperature and chemical environment, and use it to examine the morphological stability of pyrite nanocrystals formed in sulfidic environments common to the different formation routes. Physical parameters such as the supersaturation of sulfur and temperature are investigated, based on parameters obtained from first principles calculations.