Excess Mg in situ powder addition for enhancing critical current density of ex situ MgB2

In this work, ex situ MgB 2 bulks were added with (1.5 Mg + 2B) and sintered in an attempt to enhance its intergrain connectivity. The addition was varied within the range of 0–50 wt.%, and the sintering was undertaken at 700 °C, 800 °C, and 1000 °C, respectively, for 1 h. Superconducting critical temperature, T c of the samples was determined to be around 38 K as shown by the temperature dependence of susceptibility measurement. It was found that critical current density, J c increased with the increased amount of the addition. J c was further enhanced to 2 × 10 4 A cm 2 (0 T, 20 K) as the sintering temperature was raised. The increase of J c is due to improved grain coupling as a result of in situ formation of MgB 2, which fills the voids and connects the ex situ MgB 2 grains. Additionally, the grain coupling was further strengthened by solid-state self-sintering at higher temperatures. The increment of J c was accompanied by a narrower width of double-step transition of T c attributable to a more complete MgB 2 phase formation of the samples as the sintering temperature was increased. Graphical abstract