Crystal structure of mechanochemically prepared Ag2FeGeS4

Ag2FeGeS4 was synthesized as a phase-pure and highly crystalline product by mechanochemical milling from the binary sulfides and iron metal, followed by annealing in H2S atmosphere. The structure evaluation was carried out using X-ray powder diffraction with subsequent Rietveld refinements. As Fe and Ge atoms are not distinguishable using conventional X-ray methods, the chalcopyrite-type structure (space group I 4 ‾ 2 d $I‾{4}2d$ ), exhibiting a statistical distribution of Fe and Ge on Wyckoff position 4b, was considered. However, quantum-chemical calculations at hybrid density-functional level indicate that mechanochemically prepared Ag2FeGeS4 crystallizes in the kesterite-type structure (space group I 4 ‾ $I‾{4}$ ) where the cations are arranged in an ordered way. Ag2FeGeS4 is a further example of a mechanochemically prepared compound differing structurally from the commonly known polymorph exhibiting the stannite type (solid-state route).