TIN OXIDATION NUMBER AND THE ELECTRONIC-STRUCTURE OF SNS-IN2S3-SNS2 SYSTEMS

We analyze the meaning of the chemical notion of tin oxidation number from the study of several phases isolated in the SnS-In2S3-SnS2 diagram. From Sn-119 Mossbauer spectroscopy it has been concluded that two oxidation numbers II and IV exist for tin in these compounds. This has been used to make some hypotheses on the local atomic structure. Tight-binding calculations are performed to characterize Sn II and Sn IV and to check these hypotheses. We conclude that the difference between Sn II and Sn IV mainly corresponds to a variation of about 0.7 Sn 5s electrons, in agreement with Mossbauer results, and that the Sn II atoms are always in strongly distorted sites. The validity of the predicted densities of states is also checked by comparing them with available photoemission spectra.