Diamagnetic and structural characterization of orthorhombic high-temperature superconductors in the system Y–Ba–Cu–O

Abstract

Ceramic samples of the 90 K superconductor with nominal composition YBa2Cu3O7−x were made under varying preparation conditions. Some samples have a narrow transition-temperature range of about 1.5 K and a 100% "ac Meissner effect" near 77 K. The magnetic losses below 85 K were much reduced in these samples. Rietveld structure refinement in space group Pmmm using powder X-ray diffraction data showed significant oxygen vacancies in the square-planar CuO2 chains parallel to the y axis in the y–z plane, and Cu disorder about the origin along the x axis. The sample with the superior superconducting properties has the formula YBa2Cu3O6.92.