Study on the improvement of MgB2 grain connectivity by rapid heating and quenching annealing

In this paper, we used Rapid Heating, Quenching and Annealing (RHQA) method to prepare MgB2 superconducting wires and investigated their phase, microstructure, and superconducting properties. XRD results showed that RHQ process suppress the formation of impurity MgO phase, and the MgB2 phase was continuously formed during the subsequent annealing process. SEM results indicated that RHQ suppressed the excessive growth of MgB2 grains, but the reaction of the raw Mg and B powders was incomplete with wide superconducting transition width (Delta Tc). The post annealing improved the crystal quality and grain connectivity of the MgB2 phase and thus the Delta Tcbecame narrower. Compared to the conventional sample sintered at 680 degrees C for 2 h, the MgB2 wires prepared by RHQ and RHQA showed significant enhancement of superconducting properties. For conventional sintered samples, the best Jcm at 20 K was 2.84 x 104 A/cm2, for the RHQ sample, the best Jcm reached 1.02 x 105 A/cm2, and after RHQA post annealing improved Jcm to 1.43 x 105 A/cm2 under the self-field. This indicates that the RHQA treatment can effectively improve the uniformity of the superconducting wire and the connectivity between grains, thereby significantly enhancing the Jcm properties.