WC contamination or addition effect on the superconducting properties in ex situ processed MgB2 tapes using unmilled and ball milled filling powders

Effect of WC addition or contamination to MgB2 on the superconducting properties of ex situ processed sintered powders and tapes was studied systematically. Impurities such as MgB4 start to appear clearly in the mixtures of MgB2 and WC powders in the unmilled and milled states when sintered at 900 degrees C and 700 degrees C, respectively. Sintering of both unmilled and milled mixtures do not bring about carbon substitution in MgB2. The critical temperature (T-c) reduction, however, is clearly observed for tapes using the milled mixtures with WC addition amount of not less than 10 mass%, although tapes using the unmilled mixtures do not show appreciable reduction at all. The transport critical current (J(c)) property degradation is clearly observed only for tapes using the milled mixtures with the addition amount of not less than 10 mass%. This degradation is attributed to the T-c reduction of those tapes.