Microstructure and Superconducting Properties in YBa 2 Cu 3 O 7-x Ceramics Doped with Nb 2 O 5 and WO 3

The effect of the addition of Nb 2 O 5 and WO 3 on the microstructure and superconducting properties in YBa 2 Cu 3 O 7- x ceramics has been investigated. It has been found that the microstructures of the two YBa 2 Cu 3 O 7- x samples to which were added Nb 2 O 5 and WO 3 were both characterized by prism-like grains and grain boundary segregations of the added elements. The superconducting transition temperature ( T c ) showed no considerable changes in both series of samples of Nb-doped and W-doped YBa 2 Cu 3 O 7- x ceramics, while the critical current density was found to be significantly improved in the doped materials (570 A/cm 2 for one of the Nb-doped samples and 690 A/cm 2 for one of the W-doped samples were obtained at 77 K and H =0 T) compared with that (420 A/cm 2 ) in the undoped YBa 2 Cu 3 O 7- x ceramics. All samples used were sintered at 1000°C in flowing O 2 .