VALENCY STATES OF BI IN BAPB1-XBIXO3-DELTA AND BA1-XKXBIO3-DELTA SUPERCONDUCTING OXIDE

X-ray absorption measurements have been made above the L(3)-Bi(Pb) edges in Bi-based three-dimensional superconductive oxides: BaPb1-xBixO3-delta (x = 0, 0.25, 1; delta less than or equal to 0.2) and Ba1-xKxBiO3-delta (x = 0.4; delta less than or equal to 0.2). The Bi valence state as a crucial parameter for understanding superconductive properties of these oxides has been determined from XANES spectra analysis. It was found that in spite of similar Bi and Pb near-edge structures the oxygen deficiency leads to a change in the L(3)-Bi edge both for BaPbBiO and for BaKBiO while the Pb edge practically does not change for BaPbBiO. The character of the changes observed and the interpretation of the NES spectra carried out by calculation give us the opportunity to confirm that the Bi valence state differs from the Pb one. The disproportionality of Bi4+ on two different Bi valence states takes place for both compounds, but in addition to Bi3+ the second valence state is not exactly Bi5+, as it was considered earlier, but Bi3+(L) under bar(n), n = 1-2. The results obtained give evidence of a local CDW increase with oxygen deficiency for both compounds.