Physical chemistry of high-temperature superconductors; inter - and intragrain behaviour and critical current densities

Doped and undoped bismuth-strontium-calcium-cuprates Bi-Sr-Ca-Cu-O 2223, doped and undoped thallium-(barium,strontium)-calcium-cuprates (Tl,Bi,Pb)-(Ba,Sr)-Ca-Cu-O 1223 and 2223 as well as mercury-barium-calcium-cuprates Hg-Ba-Ca-Cu-O 1223 were characterised by X-ray diffraction, by scanning electron and optical microscopy as well as by transport critical current (77 K) and by resistance versus temperature measurements. The magnetic field and the temperature dependences of the dispersive and the absorption components of the low frequency ac magnetic susceptibility for the bulk superconductors as well as for some thallium based Ag - sheathed superconducting tapes were measured and analysed. Critical current densities were extracted from the experimental data via a superconducting critical state model. Specific heats of some specimens were measured within the relevant temperature interval and the jumps in specific heat and apparent contributions from Gaussian fluctuations of superconducting order parameter close to Tc were observed. X-ray Photoemission Spectra (XPS) from the core-levels as well as the XPS and Ultraviolet Photoemission Spectra (UPS) from the valence bands of some selected samples were measured and analysed. The Coulomb correlation energies were estimated from the Cu 2p3/2 and Cu 2p1/2 core- level lines accompanied by the two satellite lines and from the Auger electron spectra and the valence band spectra.