High-T_c superconductivity in perovskite oxides of the Y-Ba-Cu-O system

Abstract

Several biphasic compositions of the type Y_3-xBa_3+xCu₆O₁₄ show an onset of superconductivity in the 90-115K range, attaining zero resistance in the 70-85K range. The phase responsible for superconductivity in these compositions is a perovskite oxide of composition YBa₂Cu₃ O₇. This oxide annealed in oxygen shows the onset of superconductivity at 120K and zero resistance at 87K. YBa₂,Cu₃O₇ shows the highest Meissner effect of all oxide superconductors. The superconducting behaviour of the two perovskite oxides, Y_0.95Ba_1.95,Cu₃O₇ and Y_1.05Ba_1.95Cu₃O₇ show interesting features; a marked decrease in resistivity is observed from room temperature itself in the former oxide with zero resistance at 89K. Electron microscopy and infrared spectra of these oxides are briefly discussed.