High-temperature superconductivity in YBa₂Cu₃O₇ and related perovskite oxides: some aspects of solid state chemistry

Abstract

Thermogravimetry and Cu K-absorption edge measurements show that the superconducting YBa₂Cu₃O₇ sample (annealed in O₂) contains more oxygen than the nonsuperconducting sample annealed in N₂, the former has a less distorted structure with the actual composition not far from the ideal one. Oxides of the formula Y_1-xBa₂Cu₃O₇ (x = 0.05, 0.10 and 0.15) annealed in oxygen also possess the perovskite structure and show high-Tc superconductivity. The superconduccting transition temperature seems to generally increase with the nominal Cu³⁺/ Cu²⁺ ratio in the superconducting copper oxides. Control of the Cu³⁺/ Cu²⁺ ratio (and hence the density of states at the metal-nonmetal transition in the non-superconducting state) through the oxygen stoichiometry or an appropriate cation substitution seems to provide a basis for synthesizing high-T_c copper oxides.