Carbon Substitution and Superconducting Properties in Ex-situ Processed Tapesusing MgB₂ Powder Treated in Organic Acid Solutions

Abstract

Fe-sheathed MgB₂ superconducting tapes were prepared through an ex-situ process and powder-in-tube (PIT) technique using powders treated in organic acid solutions. The treatment realizes the substitution of carbon, derived from the remnants of the organic solvents being adsorbed onto the surface of MgB₂ grains, into boron in MgB₂ and pulverization of MgB₂grains. The amount of carbon substitution is x = 0.02−0.03 in MgB_2-xC_x. The carbon substitution is effective for increasing B_c2,and grain boundaries act as pinning centers. Therefore, this improves the J_c property of tapes in the high-magnetic-field region.Depending on the solution, the J_c values at 4.2 K and 10 T increase up to ten times compared to tapes using powders withouttreatment. These values are comparable to those obtained for the ex-situ processed tapes with the best-ever reported performance.Tapes using MgB_2-xC_x (x ≥ 0.05) powders clearly show weak grain coupling, and hence the enhancement of transport J_c is limited.