Phthalocyanine doping to improve critical current densities in MgB ₂ tapes

Phthalocyanine-doped MgB₂ tapes were prepared by the insitu powder-in-tube method. The relationships between the critical current properties, crystallinity and microstructure were studied as a function of the phthalocyanine doping level. It is found that both H_irr and H _c2 were improved when MgB₂ samples were doped with phthalocyanine, which are mainly attributed to the effective carbon substitution and enhanced flux pinning strength caused by very fine grain sizes. Furthermore, compared to pure samples, the MgO content remained almost unchanged in all doped tapes, which is very beneficial to having better grain connectivity in MgB₂. Significantly improved J_c was obtained in the phthalocyanine-doped MgB₂ tapes, especially under high magnetic fields.