Yuri L. Zuev

Enhanced flux pinning by BaZrO3 and (Gd,Y)2O3 nanostructures in metal organic chemical vapor deposited GdYBCO high temperature superconductor tapes

We have formed BaZrO3 nanocolumns and (Gd,Y)2O3 nanoprecipitates in reel-to-reel metal organic chemical vapor deposition (MOCVD) processed (Gd,Y)Ba2Cu3O7−x coated conductors and increased the critical currents (Ic) of the conductors in applied magnetic fields to remarkable levels. A (Gd,Y)Ba2Cu3O7−x tape of 1 m in length with 6.5% Zr-additions and 30% composition rich in both Gd and Y showed Ic values of 813 A/cm width at (self-field, 77 K) and above 186 A/cm width at (1 T, 77 K). The strongly enhanced flux pinning over a wide range of magnetic field orientations can be attributed to the bidirectionally aligned defect structures of BaZrO3 and (Gd,Y)2O3 created by optimized MOCVD conditions.

Enhanced and uniform in-field performance in long (Gd, Y)?Ba?Cu?O tapes with zirconium doping fabricated by metal?organic chemical vapor deposition

The influence of Zr doping in (Gd, Y)?Ba?Cu?O ((Gd, Y)BCO) tapes made by metal?organic chemical vapor deposition has been studied with a specific objective of uniform and reproducible enhancement in in-field critical current (Ic) over long lengths. 50?m long tapes with 7.5 and 10?at.% Zr doping in 1? ?m thick (Gd, Y)BCO films have been found to exhibit a sharply enhanced peak in Ic in the orientation of field parallel to the c-axis and retain 28% of their self-field Ic value at 77?K and 1?T. BaZrO3 (BZO) nanocolumn density in the cross-sectional microstructure was found to increase with increasing Zr addition. The end segments of the 50?m long tapes were found to display nearly identical angular dependence of critical current at 77?K and 1?T, indicative of the uniformity in in-field performance over this length. A 610?m long tape was fabricated with 10% Zr doping and a 130?m segment showed a 3.2% uniformity in critical current measured every meter in the orientation of -axis. A retention factor of 36% of the zero-field Ic value measured at 0.52?T over the 130?m is consistent with that obtained in short samples.

Enhanced flux pinning in MOCVD-YBCO films through Zr additions: systematic feasibility studies

Systematic effects of Zr additions on the structural and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) films deposited by metal-organic chemical vapor deposition (MOCVD) have been investigated. Detailed characterization, conducted by coordinated transport, x-ray diffraction, scanning and transmission electron microscopy analyses, and imaging Raman microscopy have revealed trends in the resulting property/performance correlations of these films with respect to varying mole percentages (mol%) of added Zr. For compositions {le} 7.5 mol%, Zr additions lead to improved in-field critical current density, as well as extra correlated pinning along the c-axis direction of the YBCO films via the formation of columnar, self-assembled stacks of BaZrO{sub 3} nanodots.

Formation of Self-Assembled, Double-Perovskite, Ba2YNbO6 Nanocolumns and Their Contribution to Flux-Pinning and Jc in Nb-Doped YBa2Cu3O7-? Films

Ba2RENbO6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa2Cu3O7-δ (YBCO) films due to their excellent chemical inertness to and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target and a Nb metal foil attached to the surface of the target resulted in epitaxial growth of YBCO films having columnar defects comprised of self-aligned Ba2YNbO6 (BYNO) nanorods parallel to the c-axis of the film. Compared to pure YBCO, YBCO+BYNO films exhibited no Tc reduction as well as superior Jc performance with higher self- and in-field Jc by a factor of 1.5–7 and also exhibited a strong Jc peak for H∥c indicative of strong c-axis correlated flux-pinning.

Engineering nanocolumnar defect configurations for optimized vortex pinning in high temperature superconducting nanocomposite wires

We report microstructural design via control of BaZrO3 (BZO) defect density in high temperature superconducting (HTS) wires based on epitaxial YBa2Cu3O7-δ (YBCO) films to achieve the highest critical current density, Jc, at different fields, H. We find the occurrence of Jc(H) cross-over between the films with 1–4 vol% BZO, indicating that optimal BZO doping is strongly field-dependent. The matching fields, Bφ, estimated by the number density of BZO nanocolumns are matched to the field ranges for which 1–4 vol% BZO-doped films exhibit the highest Jc(H). With incorporation of BZO defects with the controlled density, we fabricate 4-μm-thick single layer, YBCO + BZO nanocomposite film having the critical current (Ic) of ~1000 A cm−1 at 77 K, self-field and the record minimum Ic, Ic(min), of 455 A cm−1 at 65 K and 3 T for all field angles. This Ic(min) is the largest value ever reported from HTS films fabricated on metallic templates.

Deposition studies and coordinated characterization of MOCVD YBCO films on IBAD-MgO templates

A recently installed research-scale metal–organic chemical vapor deposition (MOCVD) system at Oak Ridge National Laboratory, provided by SuperPower, Inc., has been used to investigate processing variables for MOCVD YBCO precursors and trends in the resulting properties. Systematic studies of YBCO film growth on LaMnO3/IBAD-MgO templates were carried out by optimizing deposition temperature and oxygen flow rate. Microstructural and superconducting properties of the YBCO films were analyzed by x-ray diffraction, scanning electron microscopy and transport measurements. The identification of intermediate phases formed during the YBCO precursor transformation was investigated by coordinated reel-to-reel Raman microprobe analysis. With this combination of various characterization techniques, an improved understanding of the growth characteristics of MOCVD YBCO films was established. Finally, critical current densities greater than 2 MA cm−2 for film thicknesses of 0.8 µm were demonstrated.

Near-isotropic performance of intrinsically anisotropic high-temperature superconducting tapes due to self-assembled nanostructures

We report material and operating parameter conditions where prototype high-temperature superconducting tape conductors exhibit in-plane critical current characteristics that are essentially field orientation independent. This phenomenon is observed for specific magnetic field intensities that depend on the operating temperature and in materials having strong flux pinning by extended nanoscale structures aligned roughly along the crystalline c-axis. The effect can be described by a simple model for the field dependence of critical current density, generalized for anisotropic electronic response. This description may provide insight into means to fine tune the material properties for nearly isotropic performance characteristics at a preferred field and temperature.

Strong enhancement of flux pinning in thick NdBa2Cu3O7- δ films grown on ion-beam assisted deposition-MgO templates via three-dimensional self-assembled stacks of BaZrO3 nanodots

Thick, epitaxial NdBa2Cu3O7-δ (NdBCO) films (up to 2.1 μm) with a high density of nanoscale columnar defects parallel to the c-axis of the film were deposited on ion-beam assisted deposition-MgO templates via pulsed laser deposition. The columnar defects were composed of self-assembled BaZrO3 (BZO) nanodots. A significant enhancement in Jc for H∥c is found for these films. In addition, an overall improvement in the in-field Jc at all field orientations is observed. Compared to pure NdBCO of similar thickness, the in-field Jc at H∥c for 0.7 μm thick NdBCO+BZO film is improved by a factor of 2–4 in the field range of 0.1–4 T and 10–20 at 7–8 T at 77 K. In addition, a smaller α∼0.17 is found in the field regime where Jc∼H−α. Also, a higher maximum pinning force, Fpmax∼14 GN∕m3, is found at 3 T and a larger Hirr over 8 T is found for the NdBCO films with columnar defects.

Multifunctional, phase separated, BaTiO3+CoFe2O4 cap buffer layers for improved flux-pinning in YBa2Cu3O7?? based coated conductors

Phase separated, epitaxial, nanostructured film comprised of BaTiO3 (BTO) and CoFe2O4 (CFO) composite has been developed as a potential multifunctional cap buffer layer for improved flux-pinning in YBa2Cu3O7−δ (YBCO) films. All films were deposited by pulsed laser deposition on SrTiO3 (STO) (100) single crystal substrates. The CFO fraction and growth temperature were identified as key factors for determining the areal number density and mean diameter of the CFO nanocolumns. Compared to the reference sample grown on a pure BTO cap layer, the YBCO films grown on BTO+CFO cap layers show a remarkable improvement in isotropic flux-pinning and, consequently, Jc over the entire field and angle ranges. Transmission electron microscopy analysis confirmed the presence of a very defective YBCO layer containing a high density of randomly distributed defects at the interface area, induced by nanostructural modulation on the surface of the BTO+CFO composite cap layer.

Field, temperature, and angle dependent critical current density Jc(H,T, ) in coated conductors obtained via contact-free methods

Applications of coated conductors based on high- Tc superconductors often require detailed knowledge of their critical current density Jc as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods for obtaining the angularly dependent Jc using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.