Core-level photoemission and x-ray absorption study of Na-covered and oxygen-deficient Ba0.6K0.4BiO3-y single crystals

To study the effects of doping in Ba0.6K0.4BiO3, core-level and valence-ban d photoemission results are presented for a single crystal with various Na coverages and for an oxygen-deficient sample. It was found that the valence band and the Ba 4d, Ba 5p, Bi 5d, and O Is core levels were shifted to hig her binding energies with increasing Na coverage, consistent with an increa se in band filling, whereas for K 2p, the shift was negligible. The valence band broadens as Na is deposited but the intensity at the Fermi level stay s constant, in line with the n-type nature of the charge carriers in Ba1-xK xBiO3. The prepeak intensity in the O K edge absorption spectrum as well as the Bi 4f asymmetry were found to be lower for oxygen-deficient Ba0.6K0.4B iO3-y than for the stoichiometric samples, indicating the importance of oxy gen content for metallic Ba0.6K0.4BiO3 The asymmetry of the Bi 4f increased with Na deposition, suggesting the growth of a high binding energy compone nt with reduced valency, whereas the Ba 4d, Ba 5p, and K 2p became narrower , consistent with a decrease of the surface-core-level shifts. [S0163-1829( 98)08243-5].