Pinning behavior of glycine-doped MgB2 bulks with excellent critical current density by Cu-activated low-temperature sintering

Abstract

Abstract Mg–B system with single glycine addition was composed of MgO phase rather than MgB 2 when sintered at 600 °C for 2 to 5 h. Cu was further introduced into Mg–B–glycine system to active the low-temperature sintering efficiency, and more than 80% MgB 2 superconducting phase was successfully obtained in Cu and glycine co-doped samples sintered at 600 °C for 8 h, 12 h, and 15 h, respectively. The sample sintered for 8 h showed uncompetitive critical current density ( J c ) because of the uncompleted MgB 2 phase and the unreacted Mg phase, while the 15-h sample showed the best J c of 1.5 × 10 4 A cm −2 at 3 T and 20 K. The pinning behavior of MgO (∼20 nm) and MgCu 2 (∼10 nm), which should be responsible for the exciting current-carrying capability that the J c performance was improved over the entire field in contrast with pure MgB 2 , was systematically investigated. According to the phase identification and the microstructure observation, both the pre-generated MgO involved in the MgB 2 grains and the MgCu 2 precipitated along the steps of the screw dislocation growth mechanism could serve as effective pinning centers. Finally, we illustrated the whole sintering process of the sample sintered at 600 °C for 15 h.