Relationship between microstructure and superconducting properties of the MgB₂ bulk fabricated from the gas-solid method

The gas-solid method, discovered in recent years, has been shown to have the potential to fabricate dense MgB₂ bulks. In this study, we aimed to investigate the dominant regulation mechanism underlying the superconducting properties and microstructures of MgB₂ bulk obtained from the gas-solid method. To this end, we utilized nano computed tomography (nano CT) and transmission electronic microscopy to examine the structure of the MgB₂ bulk at the micrometer and nanometer scales, respectively. Nano-CT results revealed that the application of a mold during the gas-solid process can significantly reduce the amount of holes present in the sample. Furthermore, the reticular hole structure can be almost completely eliminated through this modification. Such a change can account for the remarkable increase in superconducting connectivity (A_f value) observed in the sample with a mold. Additionally, we found that different B powders can lead to vastly different MgO impurity particle sizes and distributions at the nanometer scale. This finding can explain the differing J_c (B) values and pinning forces observed in the corresponding samples. Overall, our correlation analysis between the structure and superconducting properties provides valuable insights into the possible regulation mechanism of MgB₂ bulk obtained from the gas-solid method. These findings may assist researchers in further improving the performance of MgB₂ bulks.