FABRICATION AND PROPERTIES OF YBA2CU3O7-DELTA-AG COMPOSITE SUPERCONDUCTING WIRES BY PLASTIC EXTRUSION TECHNIQUE

YBa2Cu3O7-delta (Y123)-Ag composite superconducting wires were fabrica ted by the plastic extrusion method which involves plastic paste makin g, die extrusion, binder burn-out and the firing process. The as-extru ded Y123-Ag wires were so flexible that they can be easily fabricated into a desirable shape. The current-carrying properties of the wire ar e dependent on sample size, sintering temperature and silver content. The critical current density, J(c), of the Y123 wire with a large cros s-section was lower than that of the wires with a small cross-section, probably due to the large self-induced magnetic field. J(c) of the Y1 23-Ag wires increased with increasing sintering temperature but abrupt ly decreased above 910 degrees C, which is close to the eutectic tempe rature of the Y-Ba-Cu-O system. A silver addition of 10-20wt% slightly increased J(c) 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 additio n, respectively), but further silver addition had a deleterious effect on J(c) (180 A cm(-2) for 30 wt% Ag addition). The small increment in J(c) in the Y123 wire with 10-20 wt% Ag addition appears to be due to the enhanced densification and the associated microstructural variati on. The decreased J, of the Y123 wire with 30 wt% Ag addition is consi dered to be due to the formation of non-superconducting phase, Y2BaCuO 5 (Y211), BaCuO2 and CuO phases via the decomposition of the Y123 phas e.