The local structures about Cu, In, and Se atoms in a series of Cu2Se–In2Se3 pseudobinary compounds have been investigated by x-ray absorption fine structure (XAFS). In K-edge XAFS and L3-edge x-ray absorption near-edge structure (XANES) suggest that CuInSe2, Cu0.9InSe1.95, Cu0.82InSe1.91, and Cu2In3Se5.5 have a nominally four-coordinated InSe4 structure, whereas CuIn3Se5 and CuIn5Se8 possess two different InSe4 structures. Cu K-edge XAFS also showed that CuIn3Se5 and CuIn5Se8 possess two different CuSe4 structures, whereas others have a CuSe4 structure. Se K-edge XANES and curve fitting analysis reveal that the Cu vacancy (VCu) gradually forms with decreasing Cu/In ratio. Moreover, the substitution of In for VCu (InCu) is observed in CuIn3Se5 and CuIn5Se8. These results were compared to the previously proposed Cu–In–Se models. We conclude that Cu0.9InSe1.95 and Cu0.82InSe1.91 have a chalcopyrite structure with VCu and that the structure of CuIn3Se5 and CuIn5Se8 is a stannite-like structure with VCu and InCu defects.
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