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

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 degreesC has been observed. For Ag sheaths, there is a strong diffusion of Mg, which does not allow the fort-nation of large amounts of MgB2 at the core. For Cu sheaths, the diffusion of Mg is stopped by the fort-nation of a MgCu2 layer around the superconducting core and an appropriate excess of Mg leads to superconducting cores with T-c approximate to 39 K and good J(c) values. Thus, the development of Cu/MgB2 composite wires is possible.