ELECTRONIC-STRUCTURE OF THE BA-DOPED (PB,CD)-1212 CUPRATES

Changes in the electronic structure for the (Pb0.5Cd0.5)(Sr2-xBax)(Ca0 .5Y0.5)Cu2O7 (0 less than or equal to x less than or equal to 0.5) sys tem associated with an semiconductor-superconductor transition have be en investigated by means of X-ray photoelectron spectroscopy. The main line of Cu2p(3/2) core level and the valence-band peak in the range 0 similar to 8 eV for the samples are broadened with Ba doping, which s uggest that there are two charge-transfer mechanisms; in-plane O2p(x,y ) --> Cu3d(x2-y2) and apical O2p(z) --> Cu3d(3z2-r2), in the system. F or the higher doped (x = 0.4 and 0.5) superconductive samples, the lat ter charge transfer seems to be more pronounced than that for the semi conductor samples (x less than or equal to 0.3), Pb4f and O 1s core-le vel spectra show that as the Ba doping content increases the oxidation state of Pb increases. The state of density in the Fermi level increa ses slightly, and a new state appears more clearly just below the Ferm i level with the partial substitution of Ba for Sr, which can be attri buted to the presence of apical O2p(z) derived holes in the (Sr,Ba)-O layers. The evidence suggests that the appearance of superconductivity in the (Pb,Cd)-1212 system has a relation with the changes in electro nic structure, especially the apical O2p(z) --> Cu3d(3z2-r2) hybridiza tion mechanism.