Improved superconducting properties of ex situ processed MgB2 tapes sintered at low temperatures under hydrogen atmosphere

Abstract

Ex situ processed Fe-sheathed MgB₂ tapes using milled powders with Te addition were sintered under Ar or H₂ atmosphere. In comparison with Ar atmosphere, sintering under H₂ improves grain connectivity in microstructure at a lower temperature. Concerning the superconducting properties, the sintering under H₂ increases the critical temperature (T_c) of the tapes by up to 2 K, as observed for in situ processed conductors heat-treated under H₂. However, the transport critical density (J_c) property shows different behavior. Whereas heat treatment under H₂ just degrades the J_c for the in situ process, sintering under H₂ improves the J_c at a lower temperature for the ex situ process. The optimal sintering temperature (T_sin) at which J_c at 4.2 K and 10 T shows best performance is lower for the sintering under H₂ than that for Ar by more than 100 °C without J_c deterioration. This J_c enhancement at low T_sins is attributed to the improved grain connectivity and the increase in the T_c, upper critical, and irreversibility fields (H_c2 and H_irr).