Zero resistance states in modified Y-Ba-Cu-O system with transition temperatures above 135 K

Superconducting transition of minor-dispersed phase in modified YBa2Cu3O7−δ samples is found to occur at around 140K. The amount of this minor phase is enough to provide zero resistivity above 135 K. The measurements of the electrical resistivity indicated that the material is stable, thermally recyclable and reproducible. X-ray analysis of the sample with the highestT c shows a major phase with perovskite-like structure witha=3·820(1) A;b=3·873(1) A andc=11·659(2) A along with several unidentified weak peaks. Magnetic measurements confirmed the mixed-phase nature with diamagnetic transition temperatures at 137,91 and 86 K. The minor phase responsible for superconductivity with zero resistivity above 135 K is about 0·4% of the bulk and its nature is still unidentified. The details of the preparation and chemical modification process and the results are presented.