A fundamental pinning mechanism has been identified in the Bi-Sr-Ca-Cu-O system. The pinning strength has been greatly increased by the introduction of calcium- and copper-rich precipitates into the sample matrix. The calcium and copper were supersaturated in the system by complete melting, and the fine calcium and copper particles precipitated during subsequent crystallization anneal to obtain the superconducting phases. The intragrain critical current density has been increased from the order of ${10}^5$ A/${\mathrm{cm}}^2$ to ${10}^7$ A/${\mathrm{cm}}^2$ at 5 T. The corresponding pinning mechanisms are discussed.

• Received 17 May 1989

DOI:https://doi.org/10.1103/PhysRevB.40.5255