Enhanced critical current density of ex situ MgB2 via control of Mg assisted sintering

In this work, ex situ MgB₂ was mixed with 0.5 mol of Mg and sintered. The sintering conditions were varied over a temperature range of 600–1000 °C for 1, 3, and 7 h, respectively. The addition of Mg during the sintering increased the partial pressure of Mg and thus suppressed the decomposition of MgB₂. Onset of critical temperature, T_c, was retained at ∼ 38 K even after the addition of Mg. By increasing the sintering temperature, magnetic critical current density, J_c at self-field, and 20 K of the ex situ samples increased consistently. With the addition of Mg for 1 h sintering, self-field J_c (20 K) was enhanced more than 20 times to 10⁴ A cm⁻² as the sintering temperature was increased. Such significant enhancement in the J_c is mainly due to the improved grain coupling aided by Mg during the short sintering.