X-ray photoelectron spectroscopic studies of CrO2 and some related chromium compounds

Core-electron and valence-band regions of crystalline CrO2, CrOOH, Cr2O3, and K2Cr2O7 have been studied. The XPS spectrum of the valence band region of CrO2 is interpretable in terms of Goodenough's band-structure model, and the finite density of states at the Fermi level for this metallic compound is readily apparent, but the band profile shows no detectable change on traversing the Curie temperature. Whereas the ratio of the multiplet splittings recorded for Cr 3s levels in CrO2 and Cr2O3 are in reasonable agreement with theory, discrepancies were noted between observed and expected multiplet intensity ratios. Some evidence for shake-up satellites was also noted. The smaller binding energies of core-electron levels in the Cr4+ solid (CrO2) compared with the corresponding binding energies in Cr3+ compounds (Cr2O3 and CrOOH) are also discussed.