ORIENTATIONS OF OXYGEN HOLE STATES AND IONICITY OF BISMUTH ATOMS IN BI2SR2CACU2O8

We report a study of the x-ray-absorption near-edge structure of the Bi L3 and 0 K edges in Bi2Sr2CaCu2O8. A comparison with the Bi L3 edges of Bi2O3 and KBiO3 indicates that the Bi atoms are in a state close to a formal valency of +3 in the superconducting compound. We attribute the peaks below 529 eV in the O K-edge spectra of Bi2Sr2CaCu2O8 to holes on the 0 sites. We investigate the symmetries of these holes by using polarized x rays. By comparing the experimental spectra with simulations based on self-consistent electronic-structure calculations, we determine that the hole states at the O sites in the Cu-O and Bi-O planes do indeed lie in these planes, while those associated with the apical O atoms of the O pyramids in the structure are aligned along the c axis.