Superconductivity near liquid nitrogen temperature in the Pb---Sr---R---Ca---Cu---O system (R= Y or rare earth)

Abstract

Superconductivity close to the boiling point of liquid nitrogen has been discovered in the P-Sr-R-Ca-Cu-O system where R is Y or rare earth. The superconducting compound has been identified as Pb₂Sr₂(R,Ca)₁Cu₃O_8+y and the structure of the R=Y compound has been solved by single-crystal X-ray diffraction methods. The structure consists of double CuO₂ sheets interleaved by (Ca,R), a unit which is common to most of the high-T_c copper oxide superconductors. A new structural feature found in this system is a double Pb---O layer separated by a sheet of copper atoms. A non-superconducting oxide of approximate composition (Y,Ca)Sr₂(Cu,Pb)₃O_7-y formed as a second phase in some preparations has been also characterized; its structure is related YBa₂Cu₃O₇.