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 Tl0.2Cr5Se8 definitely exclude the oxidation of Tl(I) to Tl(III) when Tl is removed using a topotactic redox reaction between TlCr5Se8 and bromine in acetonitrile. Alterations 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). Significant differences are observed in the valence band regions that were investigated with He I and He II radiation. For the Tl-poor sample an increased electron density at the Fermi level is observed in accordance with the higher electrical conductivity of this sample. The variations of the emissions in the region down to about 3 eV below EF can nicely be explained on the basis of the reduced Tl content and a partial oxidation of Cr(III) to Cr(IV).