Fabrication and properties of YBa2Cu3O7-δAg composite superconducting wires by plastic extrusion technique

Abstract

YBa2Cu3O7-δ (Y123)-Ag composite superconducting wires were fabricated by the plastic extrusion method which involves plastic paste making, die extrusion, binder burn-out and the firing process. The as-extruded Y123-Ag wires were so flexible that they can be easily fabricated into a desirable shape. The current-carrying properties of the wire are dependent on sample size, sintering temperature and silver content. The critical current density, Jc, of the Y123 wire with a large cross-section was lower than that of the wires with a small cross-section, probably due to the large self-induced magnetic field. Jc of the Y123-Ag wires increased with increasing sintering temperature but abruptly decreased above 910 °C, which is close to the eutectic temperature of the Y–Ba–Cu–O system. A silver addition of 10–20 wt% slightly increased Jc of the Y123 (at 77 K and 0 T, it was 140 and 250 A cm -2 for the undoped Y123 wire and the Y123 wire with 20 wt% Ag addition, respectively), but further silver addition had a deleterious effect on Jc (180 A cm -2 for 30 wt% Ag addition). The small increment in Jc in the Y123 wire with 10–20 wt% Ag addition appears to be due to the enhanced densification and the associated microstructural variation. The decreased Jc of the Y123 wire with 30 wt% Ag addition is considered to be due to the formation of non-superconducting phase, Y2BaCuO5 (Y211), BaCuO2 and CuO phases via the decomposition of the Y123 phase.