Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

Materials science challenges for high-temperature superconducting wire

Strong isotropic flux pinning in solution-derived YBa 2 Cu 3 O 7− x nanocomposite superconductor films

Strong isotropic flux pinning in solution-derived YBa2Cu3O7-x nanocomposite superconductor films.

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.

Synergetic combination of different types of defect to optimize pinning landscape using BaZrO 3 -doped YBa 2 Cu 3 O 7

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?? (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??, with ?~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.

https://iopscience.iop.org/article/10.1088/0953-2048/18/11/021/pdf

Irradiation-free, columnar defects comprised of self-assembled nanodots and nanorods resulting in strongly enhanced flux-pinning in YBa2Cu3O7−δ films

Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides

Following the discovery of type-II high-temperature superconductors in 1986 (refs 1, 2), work has proceeded to develop these materials for power applications. One of the problems, however, has been that magnetic flux is not completely expelled, but rather is contained within magnetic fluxons, whose motion prevents larger supercurrents. It is known that the critical current of these materials can be enhanced by incorporating a high density of extended defects to act as pinning centres for the fluxons. YBa2Cu3O7 (YBCO or 123) is the most promising material for such applications at higher temperatures (liquid nitrogen). Pinning is optimized when the size of the defects approaches the superconducting coherence length ( approximately 2-4 nm for YBCO at temperatures < or =77 K) and when the areal number density of defects is of the order of (H/2) x 10(11) cm(-2), where H is the applied magnetic field in tesla. Such a high density has been difficult to achieve by material-processing methods that maintain a nanosize defect, except through irradiation. Here we report a method for achieving a dispersion of approximately 8-nm-sized nanoparticles in YBCO with a high number density, which increases the critical current (at 77 K) by a factor of two to three for high magnetic fields.

Addition of nanoparticle dispersions to enhance flux pinning of the YBa2Cu3O7-x superconductor

Different mechanisms may exists as a means to provide additional or specialized enhancement of existing nanoparticulate pinning in YBa 2 Cu 3 O 7− x (YBCO) thin films. In the particular case of Y 2 BaCuO 5 (Y211) nanoparticles, Ca-doping of these nanoparticles via addition to the Y211 target material provides an additional increase to the J c ( H ). YBCO + Y211 samples were created by pulsed laser deposition with alternating targets of YBCO with Y211 and Y211 doped with Ca. Initial indications suggest that this improvement in pinning results from some scattered short-ranged self-assembly of the nanoparticles into short nanocolumns.

Inducing self-assembly of Y2BaCuO5 nanoparticles via Ca-doping for improved pinning in YBa2Cu3O7−x

Garnet-type solid-state electrolytes have significant advantages over liquid organic electrolytes but require energy-intensive sintering to achieve high density and ionic conductivity. The aim of this study is to understand the...

Pore and Grain Chemistry during Sintering of Garnet-type Li6.4La3Zr1.4Ta0.6O12 Solid-state Electrolytes

Atom probe tomography (APT) combines sub-nanometer resolution, three-dimensional chemical and isotopic imaging, and a combined ionization + detection efficiency as high as 80 %. In principle, other forms of mass spectrometry would require an analysis volume roughly an order of magnitude larger to achieve a comparable level of analytical precision. APT is thus an attractive option for analyzing nanoparticles, and several such experiments have been conducted and published to date [1-4]. However, few of these experiments have sought to analyze specific, isolated nanoparticles [5]. In this work, we present a straightforward method for creating atom probe specimens from individual nanoparticles of interest on a solid substrate, using a dual beam FIB-SEM instrument equipped with an in-situ nano-manipulator. The primary limitation of this technique is the size of the nanoparticle must be large enough to allow for manipulation, which is ultimately determined by the sharpness of the manipulator needle and the positioning precision of the nano-manipulator. Dilute solutions of commercially available nanoparticles dispersed in ethanol were created, agitated using an ultrasonic probe, and then drop cast onto silicon substrates. The particles used in the study were primarily Bi 2 O 3 and TiO 2 , ranging in size from approximately 80 nm to 200 nm. The in-situ nano-manipulator was used to pick specific particles from the substrate and place them onto an APT specimen support post of a commercially available flat-top-post array coupon, without the use of any in-situ platinum deposition. A variety of pick-and-place techniques were explored, including pre-sharpening the flat top post with the ion beam, milling a small dimple into the top of the post for the particle to rest in, and using an electron beam-curable

Preparation of Atom Probe Specimens Containing Individual Nanoparticles

Atom probe tomography (APT) has emerged as a valuable technique to study the chemistry and structure of semiconductor devices with features on the nanometer length scale [2, 3, 4]. In APT, a needle-shaped specimen is subjected to a high electric field and repeated energy pulses (either thermal or voltage), causing atoms or clusters of atoms on the apex of the tip to ionize and evaporate from the tip [5, 6]. The ions are accelerated in the electric field and directed towards a 2-dimensional position sensitive detector. The identity of the ion is determined based on its time of flight and, coupled with positional information also recorded by the detector, a 3D reconstruction of the sample is created. This technique produces detailed, chemical information with sensitivity in the range of 10’s of μg/g. However, it has been established that the chemical quantification can be biased by experimental conditions that affect the electric field in which the ions are evaporating (e.g., laser pulse energy) [7, 8]. A specific example of this occurs in phosphorous (P) doped silicon (Si) where P evaporates as different ion species depending on the applied electric field. We hypothesize this is further complicated by both P + and P2 2+ contributing signal to the peak at 31 Da, making quantification difficult. Since P is monoisotopic, the conventional approach of using natural isotope abundances as an aid for ion species identification and peak decomposition cannot be used to determine the contributions of P + and P2 2+ to the 31 Da peak. Using a reference material with a known retained dose of P (NIST SRM 2133, P implant in Si depth profile standard, [9]), we can calculate the fractions of P + and P2 2+ in the 31 Da peak with the approach outlined in Figure 1. By performing similar analyses under a variety of applied field conditions, a calibration curve is generated for P in Si measurements.

F. Meisenkothen

Papers

Addition of nanoparticle dispersions to enhance flux pinning of the YBa2Cu3O7-x superconductor

Inducing self-assembly of Y2BaCuO5 nanoparticles via Ca-doping for improved pinning in YBa2Cu3O7−x

Pore and Grain Chemistry during Sintering of Garnet-type Li6.4La3Zr1.4Ta0.6O12 Solid-state Electrolytes

Preparation of Atom Probe Specimens Containing Individual Nanoparticles

A Standards-based Approach to Dopant Quantification Using Atom Probe Tomography