Study of Ag and Cu/MgB2 powder-in-tube composite wires fabricated by in situ reaction at low temperatures

Abstract

Superconducting Ag or Cu sheathed MgB2 wires have been fabricated by conventional powder-in-tube techniques. The in situ reactions of Mg and B powders with atomic proportions of 1:2 and 1.33:2 inside Ag or Cu tubes at low temperatures have been explored. An active alloying of Mg with Ag or Cu sheaths at temperatures below 660 °C has been observed. For Ag sheaths, there is a strong diffusion of Mg, which does not allow the formation of large amounts of MgB2 at the core. For Cu sheaths, the diffusion of Mg is stopped by the formation of a MgCu2 layer around the superconducting core and an appropriate excess of Mg leads to superconducting cores with Tc ≈ 39 K and good Jc values. Thus, the development of Cu/MgB2 composite wires is possible.