Influence of hydrogen-containing argon gas on the structural parameters and superconducting properties of malic acid-doped MgB2 wires

We have studied the influence of hydrogen-containing argon gas on the structural and superconducting properties of MgB2 wires. Lattice parameters were independent of the concentration level of hydrogen in argon, while the fraction of the secondary phase, MgO, was sensitive. The MgO particles observed by scanning transmission electron microscopy were 30–50 nm in size, which is considerably larger than the appropriate size range of flux pinning centers. The sintering atmosphere conditions are a crucial issue for MgB2 wires.