Microstructure and superconducting properties in YBa2Cu3O7-x ceramics doped with Nb2O5 and WO3

The effect of the addition of Nb2O5 and WO3 on the microstructure and superconducting properties in YBa2Cu3O7-x ceramics has been investigated. It has been found that the microstructures of the two YBa2Cu3O7-x samples to which were added Nb2O5 and WO3 were both characterized by prism-like grains and grain boundary segregations of the added elements. The superconducting transition temperature (Tc) showed no considerable changes in both series of samples of Nb-doped and W-doped YBa2Cu3O7-x ceramics, while the critical current density was found to be significantly improved in the doped materials (570 A/cm2 for one of the Nb-doped samples and 690 A/cm2 for one of the W-doped samples were obtained at 77 K and H =0 T) compared with that (420 A/cm2) in the undoped YBa2Cu3O7-x ceramics. All samples used were sintered at 1000°C in flowing O2.