To improve critical current density, Jc, under magnetic fields and at 77 K, some pinning centers have been introduced into REBa2Cu3Oy 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 Jc 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 Jc-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 Jc-B properties also are discussed.
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