An X-ray spectral study of the influence on the electric structure of high Tc superconductors of the parameters determining the superconducting transition temperature

CuLsub(α) and OKsub(α) X-ray fluorescence spectra, corresponding to the Cu3d-Cu2p and O2p-O1s transitions, and XANES and EXAFS spectra (CuK, YK, BiL, PbL) have been obtained for the following series of samples: (i)YBa2Cu3Osub(7-δ)(0<δ<0.8), (ii)Lasub(2-x)SrxCuO4(0<x<0.3) and (iii)Bi2(Sr, Ca)sub(n+1)CunOsub(2n+4)(n=1,2,3), Bisub(1.8)Pbsub(0.3)Srsub(1.9)Ca2Cu3Oy. A correlation has been found between the decrease in the superconducting transition temperature (Tc) with variation in the stoichiometric parameters δ and x in series (i) and (ii), and the shift of the maximum in their CuLsub(α) spectra and the relative increase in the number of occupied states Cu3d in the upper part of the valence band. The changes in the distribution of the Cu3d and O2p densities and in the spectral parameters of the samples are discussed. (author). 9 refs., 6 figs