Microstructure and superconductivity of MgB2 synthesized by using Mg-based compound powders

MgB2 can be synthesized through a new route using Mg2Cu instead of pure Mg. When the temperature is elevated to around the melting point of Mg2Cu (568 °C), the <f>Tc</f> for Mg2Cu/B Fe-sheathed wires increases rapidly to about 37.5 K. Mg2Cu with its low melting point promotes the diffusion reaction to form a high <f>Tc</f> MgB2 at low temperatures. A lot of second phases forms with small amounts of MgB2 in the core of the wires. However, the transport <f>Jc</f> value, which is greater than 105 A/cm2 at 4.2 K in ambient fields, is rather high. Since the <f>Jc</f> value is estimated from a net-cross-sectional area of MgB2 it is expectedly high. Moreover, Mg2 Cu/B/metal-substrate layered composites were also prepared in this study. After a heat treatment at 600 °C for 10 h in a vacuum, a 50 μm thick MgB2 diffusion layer forms with a high-density microstructure. Cu is released from Mg2Cu, and collects on the surface of the diffusion layer. This behavior of Cu is similar to that of the bronzed process used for Nb3 Sn practical conductors. [Copyright &y& Elsevier]