Use of X-Ray Absorption Spectra as a 'Fingerprint' of the Local Environment in Complex Chalcogenides

The local environment of tin, titanium, iron, and sulfur in spinel compounds Cu2FeSn3S8 and Cu2FeTi3S8 was studied by X-ray absorption spectroscopy (XAS) at the titanium, iron, sulfur K edges, and the tin LI-edge. As detailed calculations of the electronic structure of these compounds are difficult to carry out due to the large number of atoms contained in the unit cell, the XAS spectra of the spinels are compared to those of relatively simple binary sulfides like SnS2, TiS2, and FeS. Indeed, the metal environments in these binary compounds are very similar to those in the spinels, and they can be considered good model compounds allowing the interpretation of electronic transitions observed in the spectra of quaternary phases. In the latter, the bottom of the conduction band is mainly formed by Sn 5s–S 3p, Sn 5p–S 3p antibonding states for the tin-based compounds and by Ti 3dt2g–S 3p, Ti 3deg–S 3p antibonding states for the titanium-based compounds. It it shown that the local environment of iron atoms remains unchanged when substituting tin with titanium atoms, according to a topotactic substitution.