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

Abstract Effect of WC addition or contamination to MgB 2 on the superconducting properties of ex situ processed sintered powders and tapes was studied systematically. Impurities such as MgB 4 start to appear clearly in the mixtures of MgB 2 and WC powders in the unmilled and milled states when sintered at 900 °C and 700 °C, respectively. Sintering of both unmilled and milled mixtures do not bring about carbon substitution in MgB 2 . 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.