Evidences for the formation of chromium in the unusual oxidation state Cr(IV) - III. Experimental electronic structure of the channel compounds TlxCr5Se8 (x = 1 and 0.2)

The X-ray photoemission core level spectra of TlCr5Se8 and Tl0.2Cr4Se8 defi nitely exclude the oxidation of Tl(I) to Tl(III) when TI is removed using a topotactic redox reaction between TlCr5Se8 and bromine in acetonitrile. Al terations are only observed for the multiplett structure of the Cr 3s core level giving evidences for a partial oxidation of Cr(III) to Cr(IV), Signif icant differences are observed in the valence band regions that mere invest igated with He I and He II radiation. For the TI-poor sample an increased e lectron density at the Fermi level is observed in accordance with the highe r electrical conductivity of this sample. The variations of the emissions i n the region down to about 3 eV below E-F can nicely be explained on the ba sis of the reduced Tl content and a partial oxidation of Cr(III) to Cr(IV), (C) 1999 Academic Press.