A new model of two directional J_c distributions for Bi ₂Sr₂CaCu₂O₈ materials

E-J properties of the high-T_c materials are related to the distribution of the local critical current density J_c. From the previous results on Bi2212 thick films and practical Ag-sheathed Bi2212 tapes, we found that the distribution of the local J_c is much affected by microstructures, and the local J_c distribution becomes broad and asymmetric for well aligned plate-like Bi2212 grains. However, from a viewpoint of microstructures, the origin of the asymmetric J_c distribution remains unclear. In order to understand the relationship between the J _c distribution of Bi2212 materials and microstructure, we propose a "two directional J_c distribution model". In this model, the difference of the local J_c distributions for various kinds of Bi2212 samples was explained in terms of the two different directional current flows and the aspect ratio of the grains. Moreover, the possibility of the small n-value even for high J_c materials in Bi2212 is also shown.