Enhancement of critical current densities of powder-in-tube processed MgB2 tapes by using MgH2 as a precursor powder

We investigated the effect of starting powder on the microstructure and superconducting properties of MgB2 tapes prepared by a powder-in-tube technique. Two kinds of powder mixtures, Mg + B and MgH2 + B, were used as precursors. When using the mixture of Mg + B, carbon-steel (CS) sheaths reacted with B, and Fe,B (x = I and 2) was formed. This brought about a decrease in the density of the MgB2 core and, hence, a low critical current density (J(c)). On the other hand, we found that the mixture of MgH2 + B was effective in suppressing the formation of Fe,,B and obtaining a high density of the core layer. The J(c) values of the tapes prepared using the mixture of MgH2 + B were about twice as large as those prepared using the mixture of Mg + B and reached 1600 A cm(-2) at 4.2 K and 10 T. This is higher than that of the CS-sheathed MgB2 tapes prepared with MgB2 powder.