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

Mg-B system with single glycine addition was composed of MgO phase rather than MgB2 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% MgB2 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 (Jc) because of the uncompleted MgB2 phase and the unreacted Mg phase, while the 15-h sample showed the best Jc of 1.5 × 104 A cm−2 at 3 T and 20 K. The pinning behavior of MgO (∼20 nm) and MgCu2 (∼10 nm), which should be responsible for the exciting current-carrying capability that the Jc performance was improved over the entire field in contrast with pure MgB2, was systematically investigated. According to the phase identification and the microstructure observation, both the pre-generated MgO involved in the MgB2 grains and the MgCu2 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.