The microstructural factors limiting the critical current density Jc have been investigated for the silver-sheathed Bi2223 tapes prepared by the powder-in-tube technique. In a hierarchy among them, which factor is the most effective in determining Jc depends on how extensively each of them occurs. The Jc was found to increase when the volume fraction of 2223 phase increases, suggesting the importance of the connectivity among 2223 grains. The Jc also increased with decreasing amount of residual carbon. The temperature and magnetic field dependences of Jc indicated characteristics of Josephson currents through superconducting–normal–superconducting barriers. After a discussion based on the alternative current limiting mechanisms proposed up to now, it is suggested that the homophase grain boundary limits the Jc.

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