ELECTRONIC-STRUCTURE OF BI2CUO4

The electronic structure of a Bi2CuO4 Single crystal is investigated b y x-ray photoelectron (XPS), x-ray Auger-electron (XAES), and electron -energy-loss (EELS) spectroscopies. The analysis of the XPS and XAES d ata confirms that Bi2CuO4 is a charge-transfer insulator with a band g ap of about 2 eV, while the Cu-O bond in Bi2CuO4 is more ionic than in CuO and the Bi2Sr2CaCu2O8-delta superconductor. Furthermore, the dens ity of the empty states is tentatively described from a combined analy sis of the EELS and XPS data and some electronic transitions are ident ified from the EELS spectra.