Excellent J_c in the low-temperature sintered MgB₂ superconductors consisted of uncompleted MgB₂ phase and residual Mg

Though low-temperature sintering of MgB₂ superconductors below Mg melting point can effectively depress volatility of Mg and increase sintering density, its development was limited in recent years for the reason that it usually took very long time to form complete MgB₂ phase with excellent J_c at low temperature. In present work, significantly improved J_c was surprisingly obtained in the MgB₂ samples sintered at 575 C for only 5 h after short-time ball milling, even though formation of MgB₂ phase is not completed and lots of residual Mg is still present in these samples. The grain connectivity in prepared samples is obviously improved compared to referred MgB₂ sample sintered at high temperature, which is responsible for the improvement of J_c. The method developed in present work seems bring a new opportunity for the development of low-cost practical MgB₂ superconductors with improved J_c without using expensive nanometer-size dopants or high-temperature sintering