Shape and thermodynamic stability of pyrite FeS2 nanocrystals and nanorods

The pyrite polymorph of iron disulfide (FeS2) has been attracting considerable attention, as it shows promise for solar energy conversion devices, solid-state batteries, and catalysis. As-prepared FeS2 powders naturally displayed rod-like morphologies, but if tailor-made pyrite nanocrystals and nanorods are to be reliably exploited in future devices, it is desirable to be able to predict and precisely control the shape (and aspect ratio) of FeS2, and to understand the morphological stability under various conditions. Therefore, we have begun by investigating the relationship between size, shape, axial orientations, and aspect ratio of unpassivated FeS2 nanostructures, using a thermodynamic model and energetic parameters calculated from first principles. The results show that the unusual morphologies such as the decahedral pyritohedron are less likely at the nanoscale than they are macroscopically, and that the preferred orientation of 1-D FeS2 nanostructures is likely to be defined by kinetics, irrespective of aspect ratio.