The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications of HTS materials, in particular electric-power applications. For many potential applications, high critical currents in applied magnetic fields are required. It is well known that columnar defects generated by irradiating high-temperature superconducting materials with heavy ions significantly enhance the in-field critical current density. Hence, for over a decade scientists world-wide have sought means to produce such columnar defects in HTS materials without the expense and complexity of ionizing radiation. Using a simple and practically scalable technique, we have succeeded in producing long, nearly continuous vortex pins along the c-axis in YBa2Cu3O7−δ (YBCO), in the form of self-assembled stacks of BaZrO3 (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of ∼2–3 nm and an areal density (‘matching field’) of 8–10 T for 2 vol.% incorporation of BaZrO3. In addition, four misfit dislocations around each nanodot or nanorod are aligned and act as extended columnar defects. YBCO films with such defects exhibit significantly enhanced pinning with less sensitivity to magnetic fields H. In particular, at intermediate field values, the current density, Jc, varies as Jc∼H−α, with α∼0.3 rather than the usual values 0.5–0.65. Similar results were also obtained for CaZrO3 (CZO) and YSZ incorporation in the form of nanodots and nanorods within YBCO, indicating the broad applicability of the developed process. The process could also be used to incorporate self-assembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials.

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The critical current density J c flowing in thin YBa 2 Cu 3 O 7−␦ ͑YBCO͒ films of various thicknesses d has been studied magnetometrically, both as a function of applied field H and temperature T, with a central objective to determine the dominant source of vortex pinning in these materials. The films, grown by a BaF 2 ex situ process and deposited on buffered rolling assisted biaxially textured substrates ͑"RABiTS"͒ substrates of Ni-5 % W, have thicknesses d ranging from 28 nm to 1.5 m. Isothermal magnetization loops M͑H ; T͒ and remanent magnetization M rem ͑T͒ in H = 0 were measured with H ʈ c-axis ͑i.e., normal to film plane͒. The resulting J c ͑d͒ values ͑obtained from a modified critical state model͒ increase with thickness d, peak near d ϳ 120 nm, and thereafter decrease as the films get thicker. For a wide range of temperatures and intermediate fields, we find J c ϰ H −␣ with ␣ ϳ͑0.56-0.69͒ for all materials. This feature can be attributed to pinning by large random defects, which theoretically has power-law exponent ␣ =5/8. Calculated values for the size and density of defects are comparable with those observed by TEM in the films. As a function of temperature, we find J c ͑T , sf͒ϳ͓1−͑T / T c ͒ 2 ͔ n with n ϳ 1.2-1.4. This points to "␦T c pinning" ͑pinning that suppresses T c locally͒ in these YBCO materials.

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