Microstructures of REBa₂Cu₃O_y films containing artificial pinning centers of various dimensions

To improve critical current density, J_c, under magnetic fields and at 77 K, some pinning centers have been introduced into REBa₂Cu₃O_y films (RE: rare earth elements). Pinning centers have been distinguished as one-dimensional, two-dimensional or three-dimensional artificial pinning centers (APCs) on the basis of their structural dimension. One-dimensional and three-dimensional APCs have considerably improved J_c as a result of our efforts. For example, BaZrO₃ or BaSnO₃ nanorods are significantly effective one-dimensional APCs. It is found that the nanorod structure can be controlled and the J_c-B properties vary depending on the nanorod structure. Moreover, the principle of two-dimensional APCs, which have been successfully designed in a multilayer structure, has been clarified. In this paper, the microstructures of the one- and two-dimensional APCs, such as the nanorods and the boundaries, are described in particular. The J_c-B properties also are discussed.