Strong influence of the YBa₂Cu₃O₇ grain size on critical current densities of thick YBa₂Cu₃O ₇ layers made by a metal-organic deposition process

We correlate the critical current performance of thick film second-generation YBa₂Cu₃O₇ (YBCO) coated conductors, made by metal-organic deposition, with specimen grain size. The transport critical current densities, J_c^T, of these conductors were observed to be inversely proportional to YBCO grain size in the 5-40νm size range. Analysis of magnetic hysteresis curves of the conductors and transmission electron microscopy data from a large YBCO grain revealed that the reduced J_c^T in tapes with large YBCO grain size is due to the accumulation of secondary phase precipitates within the grains near the periphery of, and in, the grain boundaries. Grain size is determined to be one of the important factors in determining J_c^T of YBCO coated conductors made by the metal-organic processes.