Evaluation of the Effect of Area Factors on the Grain Connectivity of Ex-Situ ${\rm MgB}_{2}$ Cores

The J _c-B performance of ex-situ MgB₂ tape is thought to depend on the grain-boundary coupling between the grains of an ex-situ MgB₂ core and between particles within a grain. This work investigates the influence of these area-dependent factors on the J _c-B performance and the measured grain connectivity of ex-situ MgB₂ cores. While the influence of area factors on the J _c - B performance of ex-situ MgB₂ tapes is small, the effect on measured grain connectivity is larger. Therefore, the relationship between the J _c - B performance of ex-situ MgB₂ tape and grain connectivity should carefully take this phenomenon into account. Moreover, this study reveals that different ways to evaluate the grain connectivity have advantages and disadvantages for detecting the influence of the area factors. We propose an evaluation guideline for the grain connectivity of ex-situ MgB₂ cores in order to analyse the reasons for area-dependent changes. We believe that this work will improve our understanding of grain connectivity and allow it to be used as feedback in investigations of the fabrication of ex-situ MgB₂ tape with high J _c - B performance.