High-temperature superconductivity (Tc0=82 K) in tetragonal Y0.5Ca0.5Ba1.5La0.5Cu3O6.88

A comparative study of structure and electric properties of two series of solid solutions with heterovalent substitution of YBa1-xLaxCu3O7±δ and Y1-xCaxBa1-xLaxCu3O7-δ (x=0.25; 0.5 and 0.75) whithin which a monotype change of crystal symmetry is detected, is conducted. With x=0.25 solid solutions of both compositions are rhombic, at x=0.5 and 0.75-tetragonal. It is ascertained that calcium introduction leads to a considerable increase of Tczero of tetragonal phases: from 60 to 82 K at x=0.5 and from 0 to 75 K for x=0.75. For samples with x=0.25 Tczero equals to 84 and 74 K respectively. By means of DTA and TQ it is shown that Y0.5Ca0.5Ba1.5La0.5Cu3O6.88 composition tetragonal sample possessing Tczero=82 K, appeass to be more thermostable as compared to YBa2Cu3O7-δ. Investigation results testify to a considerable role of CuO2 planes in the occurrence of high-temperature superconductivity in the compounds with YBa2Cu3O7-δ type structure