On the superconductivity in in situ synthesized MgB2 tapes

Single core stainless steel (SS) sheathed MgB₂ tapes have been made by the powder-in-tube (PIT) method using commercial Mg and B powders in two series, one with nominal composition and the other with excess Mg. The electrical resistivity and susceptibility measurements have been carried out to evaluate residual resistivity ratio (RRR), the coherence length ξ(0) and critical current density J_C(T) in these tapes. Detailed structural analysis of the core material has been carried out to correlate the superconducting properties with the crystallinity. In the optimized growth condition the MgB₂ tapes exhibited an estimated J_C of ∼1.4×10⁷ A/m² at 39.45 K in zero field and the zero temperature coherence length is found to be ∼68 Å. MgB₂ tapes fabricated from starting powders having nominal Mg-composition have been shown to exhibit higher J_C than those fabricated from excess magnesium composition of the starting powders. The strained lattice together with the presence of nanosized MgO inclusion having size smaller than the coherence length, are shown to be responsible for the observed higher J_C.