Investigation of Nb–B Diffusion and the Superconducting Properties of MgB2/Nb/Cu Tapes

The Nb–B diffusion behaviors and their effects on the superconducting properties of MgB2/Nb/Cu tapes were investigated. Two relevant samples of the Nb–B diffusion couples and monocore MgB2/Nb/Cu tapes were prepared with the same standard in situ PIT method, respectively. And both the samples were sintered at 650, 750, 850, and 950°C for 2 hours, respectively. It has been found that Nb–B interface is invisible in the diffusion couples sintered at low temperatures as 650°C, correspondingly the superconducting properties of MgB2 tapes are superior to those of the ones sintered at the other three temperatures. With the heating temperature increasing, Nb–B interface, mainly NbB2 with a little NbB, appears and becomes thicker gradually in the Nb–B diffusion couples. The corresponding superconducting properties of MgB2 tapes follow the similar patterns: within the range from 650°C to 950°C, the higher the sintering temperature, the poorer the superconducting performances, because the Nb–B diffusion in MgB2 tapes could cause the property degradations of MgB2/Nb tape. As extended to the actual fabrications of Nb sheathed MgB2 tapes or wires, suitable sintering temperature range should be from 650°C to 750°C for the desired performances.