Irradiation-free, columnar defects comprised of self-assemblednanodots and nanorods resulting in strongly enhanced flux-pinning inYBa2Cu3O7−δ films

Abstract

The development of biaxially textured, second-generation, high-temperaturesuperconducting (HTS) wires is expected to enable most large-scale applicationsof HTS materials, in particular electric-power applications. For many potentialapplications, high critical currents in applied magnetic fields are required. It iswell known that columnar defects generated by irradiating high-temperaturesuperconducting materials with heavy ions significantly enhance the in-field criticalcurrent density. Hence, for over a decade scientists world-wide have sought meansto produce such columnar defects in HTS materials without the expense andcomplexity of ionizing radiation. Using a simple and practically scalable technique,we have succeeded in producing long, nearly continuous vortex pins along thec-axisin YBa2Cu3O7−δ (YBCO), in the form of self-assembled stacks ofBaZrO3 (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 ofBaZrO3. In addition, four misfit dislocations around each nanodot or nanorod arealigned and act as extended columnar defects. YBCO films with such defectsexhibit significantly enhanced pinning with less sensitivity to magnetic fieldsH. In particular, at intermediate field values, the current density,Jc, variesas Jc∼H−α,with α∼0.3 rather than the usual values 0.5–0.65. Similar results were also obtained forCaZrO3 (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 usedto incorporate self-assembled nanodots and nanorods within matrices of other materials fordifferent applications, such as magnetic materials.