Massive enhancement in flux-pinning by columnar defects via 3D self-assembly of non-superconducting nanodots within superconducting films on technical substrates

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 [1-10]. For many potential applications, high critical currents in applied magnetic fields are required. It is wellknown that columnar defects generated by irradiating high temperature superconducting materials with heavy-ions significantly enhance the in-field critical current density [2-4]. 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. For 0.2 μm thick YBCO films, the nanodots and nanorods have a diameter of ~2-3 nm and an areal density ("matching field") of 8-10 tesla 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 selfassembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials. Finally, we have further extended this work to 3 μm thick YBCO films and have demonstrated short segments of a superconducting wire which meets or exceeds performance requirements for many large-scale applications of high temperature superconducting (HTS) materials, especially those, which require a high supercurrent and/or a high engineering critical current density in applied magnetic fields. This overview chapter is a compilation of the data recently published in three papers by Goyal et al. [11] and Kang et al. [12] and Li et al. [13].