Fabrication and magnetoresistivit of ex-situ processed MgB_2/Fe monofilament tapes without any intermediate annealing

摘要

We have fabricated MgB_2/Fe monofilament wires and tapes by a powder-in tube (PIT) technique, using an ex-situ process without any intermediate annealing. MgB_2/Fe monofilament tapes were annealed at 650-1,050℃ for 60 min and 950℃ for 30-240 min. We have investigated the effect of annealing temperatures and times on the formation of MgB_2 phase, activation energy, temperature dependence of irreversibility field H_(irr)(T) and upper critical field H_(c2)(7), transition temperature (T_c), lattice parameters (a and c), full width at half maximum, crystallinity, resistivity, residual resistivity ratio, active cross-sectional area fraction and critical current densities. We observed that the activation energies of the MgB_2/Fe monofilament samples increased with increasing annealing temperature up to 950℃ and with increasing annealing time up to 60 min while it decreased with increasing magnetic field. For the MgB_2/Fe monofilament tape, the slope of the H_(c2)-T and H_(irr)T curves decreased with increasing annealing temperature from 850 to 950℃ as well as with increasing annealing time from 30 to 60 min. The transport and microstructure investigations show that T_c, J_c and microstructure properties are remarkably enhanced with increasing annealing temperature. The highest value of critical current density is obtained for the sample annealed at 950℃ for 60 min. The J_c and T_c~(offfset) values of the sample annealed at 950℃ for 60 min were found to be 260.43 A/cm~2 at 20 and 38.1 K, respectively.