Study of MgO formation and structural defects inin situprocessed MgB2/Fe wires

We fabricated MgB 2 /Fe wire by a powder-in-tube (PIT) technique, using an in situ process. All wire samples were sintered for 30 min at different sintering temperatures ranging from 650 to 1000 °C. We found strong correlations among crystallinity, critical current density ( J c ), irreversibility field ( H irr ), upper critical field ( H c2 ), and microstructures for all MgB 2 /Fe wires. We observed that the sample with the lowest sintering temperature, ∼ 650 °C, had a larger lattice strain, J c , change in resistivity Δρ(ρ 300 K –ρ 40 K ), H irr , and H c2 , but a lower density and residual resistivity ratio (RRR). Based on the relationships between all these superconducting and microstructure parameters, grain boundaries are likely to be acting as the predominant pinning centers for MgB 2 , so grain growth of MgB 2 corresponds to a reduction of effective pinning. It should be noted that changes in the MgO fraction within the MgB 2 matrix were almost independent of the sintering temperature. This indicates that most MgO may be coming from the starting material.