In situ resistance measurements and low temperature synthesis of superconducting MgB2 bulk samples

Superconducting MgB2 bulk samples were simply sintered by heating stoichiometric mixture of Mg and B in vacuum. In situ resistance measurements were performed carefully in order to find the best annealing process. The in situ resistance measurements exhibit a decrease in resistance when the heating temperature is increased. The measurements suggested that the Mg powder melting temperature was below 650 °C and the temperature of 800 °C was higher than required. A MgB2 bulk sample sintered at 750 °C has a superconducting transition temperature of Tc(R=0)=40.3 K, higher than that sintered at 680 or 810 °C.