High Tc Superconductivity in Metallic Oxide Compounds

Different preparation techniques were elaborated for obtaining La–Ba–Cu–O, La–Sr–Cu–O, Y–Ba–Cu–O, Y–Sr–Cu–O, Y–La–Ba–Cu–O and Y–La–Ba–Sr–Cu–O metallic oxide superconductors. Physical and chemical properties of them were analysed by thermogravimetry, powder X-ray, SEM, electron microprobe and SIMS which hint at a multiple-phase structure of the compounds in question. T c for one part of samples is higher than 50 K and for the other part falls into liquid nitrogen temperature range above 90 K. Superconductivity was confirmed by magnetic measurements too. A change in Fermi-surface topology due to the increasing additive material content and a supplementary percolation process can be treated as the main effects for high-T c superconductivity.