Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

From the stone ages to modern history, new materials have often been the enablers of revolutionary technologies.[1] For a wide variety of envisioned applications in space exploration, energy-efficient aircraft, and armor, materials must be significantly stronger, stiffer, and lighter than what is currently available. Carbon nanotubes (CNTs) have extremely high strength, [2][3][4][5] very high stiffness, [6,7] low density, good chemical stability, and high thermal and electrical conductivities.[8]These superior properties make CNTs very attractive for many structural applications and technologies. Here we report CNT fibers that are many times stronger and stiffer per weight than the best existing engineering fibers and over twenty times better than other reported CNT fibers. Additionally, our CNT fibers are nonbrittle and tough, making them far superior to existing materials for preventing catastrophic failure. These new CNT fibers will not only make tens of thousands of products stronger, lighter, safer, and more energy efficient, but they will also bring to fruition many envisioned technologies that have been to date unavailable because of material restrictions. Strong, stiff, and lightweight are critical property requirements for materials that are used in the construction of space shuttles, airplanes, and space structures. These properties are assessed by a material's specific strength and specific stiffness, which are defined as the strength or stiffness (Young's modulus) of a material divided by its density.[9] The combination of high strength, high stiffness, and low density affords CNTs with extremely high values for specific strength and specific stiffness. The most effective way to utilize these properties is to assemble CNTs into fibers. However, despite extensive worldwide efforts to date, the specific strength and specific stiffness of CNT fibers that have been reported by various research groups are much lower than currently available commercial fibers. [10][11][12][13][14][15][16][17][18][19][20][21][22] In early studies, researchers attempted to reinforce polymer fibers with short CNTs, but the reinforcement was limited by several issues, including poor dispersion, poor alignment, poor load transfer, and a low CNT volume fraction. [10][11][12][13][14][15] Recently, pure CNT fibers (also called yarns)were reported with and without twisting. [16][17][18][19][20][21][22] For example, Zhang et al. [20] demonstrated that spinning from aligned CNT arrays could significantly improve the strength of CNT fibers by twisting them. However, to date no breakthrough has been reported in the specific strength and specific stiffness of CNT fibers.Here we report CNT fibers with values for specific strength and specific stiffness that are much higher than values reported for any current engineering fibers as well as previously reported CNT fibers. As shown in Figure 1, the specific strength COMMUNICATION 4198

Arrays of well‐aligned, ca. 4.7 mm long carbon nanotubes (CNTs) are grown in a simple, safe, and cost‐effective manner using an efficient Al2O3/Fe catalyst prepared by an ion‐beam assisted deposition technique (see figure). Importantly, the as‐synthesized CNT arrays with lengths ranging from 500 μm to 1.5 mm are conducive to spinning, and CNT fibers spun from such long CNT arrays show remarkably improved tensile strength.

High critical current densities (Jc) in thick films of the Y1Ba2Cu3O7–δ (YBCO, Tc ≈ 92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application‐dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect‐free conductor in which the grain‐to‐grain connectivity maintains levels of inter‐grain Jc that are comparable to the intra‐grain Jc. That is, high critical current (Ic) YBCO coated conductors must contain engineered inhomogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high‐performance YBCO coated‐conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano‐engineer the microstructure for tuneable superconducting wires. Multi‐scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher Ic wires for large‐scale, commercial application are discussed within the context of these recent advances.

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