Eduard Galstyan

Critical current density above 15 MA cm−2 at 30 K, 3 T in 2.2 μm thick heavily-doped (Gd,Y)Ba2Cu3Ox superconductor tapes

A critical current (Ic) value of 3963 A/12 mm, corresponding to a critical current density (Jc) of 15 MA cm−2 has been achieved at 30 K, 3 T in the orientation of field parallel to the c-axis (B||c) in 2.2 μm thick film (Gd,Y)BaCuO tapes with 20 mol% Zr addition made by metal organic chemical vapor deposition. This Jc level is more than a factor of four higher than the Jc values of 7.5 mol% Zr-added tapes, which are an industry benchmark. The critical current values in a magnetic field of 3 T parallel to the c-axis in the 2.2 μm thick, 20 mol% Zr-added tape reached 2833 A/12 mm (10.1 MA cm−2), 1881 A/12 mm (7.1 MA cm−2) and 805 A/12 mm (3.1 MA cm−2) at 40 K, 50 K and 65 K respectively. Such high critical current values were possible because of maintaining a strong alignment of BaZrO3 nanocolumns along the c-axis over the entire film thickness.

Investigation of Delamination Mechanisms in IBAD-MOCVD REBCO Coated Conductors

In recent years, remarkable technical advances have been achieved in the development of Rare-earth-Ba-Cu-O (REBCO) based coated conductors for large-scale applications. For coil-based applications (e.g., motors, generators, magnets), in addition to high critical current density under applied field, the conductor also needs to maintain mechanical integrity when exposed to transverse tensile stresses typically found in impregnated coils. In this study, we present a detailed analysis of the microstructure of REBCO coated conductors delaminated by application of transverse tensile stresses, in an effort to gain insight into the underlying mechanisms of failure and the weak link in the multilayer conductor architecture. In addition, we perform statistical analysis of delaminated areas of multilayer coated conductors subjected to c-axis pull experiments. Results on optical image correlation of fractured surfaces, analysis of buffer layer defects, and analysis of variance of data scatter are presented.

Light-Induced Covalent Immobilization of Monolayers of Magnetic Nanoparticles on Hydrogen-Terminated Silicon

Specifically tailored ω-alkenyl-1-carboxylic acids were synthesized for use as surfactants in the single-step preparation of manganese ferrite (MnFe2O4) nanoparticles (NPs). Monodisperse manganese ferrite NPs terminated with ω-alkenyl moieties were prepared via a one-pot reaction at high temperature without the need of ligand exchange. Using this approach, simple adjustment of the rate of heating allowed precise tuning of the size of the nanoparticles, which were characterized in bulk form by transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). These surfactant-coated magnetic nanoparticles were then deposited onto hydrogen-terminated silicon(111) wafers and covalently anchored to the surface by UV-initiated covalent bonding. Analysis by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) confirmed that the UV treatment led to covalent immobilization of the NPs on the silicon surface with a consistent packing density across the surface. The magnetic properties of the stable, surface-bound nanoparticle arrays were characterized using a superconducting quantum interference device (SQUID) magnetometer. The materials and methods described here are being developed for use in bit-patterned ultrahigh density magnetic recording media and nanoscale biomagnetic sensing.

Requirements to achieve high in-field critical current density at 30 K in heavily-doped (Gd,Y)Ba 2 Cu 3 O x superconductor tapes

Critical current densities (J c) above 15 MA cm−2 have been achieved at 30 K, 2.5 T (B||c) in (Gd,Y)–Ba–Cu–O tapes with 20–25 mol.% Zr addition. The optimal compositions of Gd + Y, Ba + Zr and Cu to achieve lift factor in critical current above 6 at 30 K, 2.5 T (B||c) have been determined by development of a composition map of the performance of heavily-doped (Gd,Y)–Ba–Cu–O tapes. An inverse relationship is found between the critical current density at 77 K, 0 T and the lift factor in critical current at 30 K, 2.5 T (B||c). It is discovered that a J c of 15 MA cm−2 at 30 K, 2.5 T (B||c) is achievable only in tapes with a J c between 2.5 and 3.8 MA cm−2 at 77 K, 0 T.

Effect of High BZO Dopant Levels on Performance of 2G-HTS MOCVD Wire at Intermediate and Low Temperatures

Flux pinning in REBCO (rare-earth Ba-Cu-O) by self-assembly of BZO (barium zirconate) nanorods has emerged as one of the most prominent techniques for improving the in-field performance of 2G-HTS wire in terms of Ic and angular Ic anisotropy. In our previous study on metalorganic chemical vapor deposition REBCO wire, an optimum performance was found for 7.5% Zr at 1 T, 77 K, while further increase in Zr content resulted in Ic and Tc degradation. However, recent results indicate that the pinning performance at high Zr content actually surpasses that of the 7.5% Zr wire at intermediate and low temperatures. In-depth understanding of the effect of high Zr levels on REBCO provides a strong potential for further substantial increase in pinning performance at high Zr content if the unwanted effects can be minimized by process modification. In this study, we analyze the effect of high Zr doping levels on REBCO properties with emphasis on microstructure analysis. Structural properties as a function of BZO dopant level have been analyzed using X-ray reciprocal space maps and transmission electron microscopy, while the performance has been characterized using angular in-field Ic characterization up to 9T at temperatures of 20-77 K.

Screen-printing of ferrite magnetic nanoparticles produced by carbon combustion synthesis of oxides

The feasibility of screen-printing process of hard ferrite magnetic nanoparticles produced by carbon combustion synthesis of oxides (CCSO) is investigated. In CCSO, the exothermic oxidation of carbon generates a smolder thermal reaction wave that propagates through the solid reactant mixture converting it to the desired oxides. The complete conversion of hexaferrites occurs using reactant mixtures containing 11 wt. % of carbon. The BaFe12O19 and SrFe12O19 hexaferrites had hard magnetic properties with coercivity of 3 and 4.5 kOe, respectively. It was shown that the synthesized nanoparticles could be used to fabricate permanent magnet structures by consolidating them using screen-printing techniques.

High Performance 2G-HTS Wire Using a Novel MOCVD System

We present the development of a novel Metal Organic Chemical Vapor Deposition (MOCVD) system aimed at producing high performance 2G-HTS wire in the ARPA-E GRIDS program on Superconducting Magnetic Energy Storage. A susceptor-free MOCVD system with non contact optical temperature monitoring and highly laminar parallel flow in a confined volume has been developed to address the issues of a-axis grain formation and low precursor conversion efficiency in conventional MOCVD designs. For the first time, near-1000 A/12 mm critical current tapes have been achieved by MOCVD in single pass deposition of 1.8-μm REBCO (RE = rare earth) on IBAD-MgO/LMO substrates. In addition, completely a-axis free films have been grown to thickness up to 4 μm, while the precursor conversion efficiency has been increased by 40%. The system and REBCO film characteristics, as well as further development aims will be presented.

Microstructure Characteristics of High Lift Factor MOCVD REBCO Coated Conductors With High Zr Content

We report the microstructural characteristics of high levels of Zr-added REBa2Cu3O7-x (RE = Gd, Y rare earth) coated conductors fabricated by Metal Organic Chemical Vapor Deposition (MOCVD). The enhancements of the lift factor defined as a ratio of the in-field (3 T, B ∥ c-axis) critical current density (Jc) at 30 K and self-field Jc at 77 K have been achieved for Zr addition levels of 20 and 25 mol% via optimization of deposition parameters. The presence of strong flux pinning is attributed to the aligned nanocolumns of BaZrO3 and nanoprecipitates embedded in REBa2Cu3O7-x matrix with good crystal quality. A high density of BZO nanorods with a typical size 6-8 nm and spacing of 20 nm has been observed. Moreover, the high Zr content was found to induce a high density of intrinsic defects, including stacking faults and dislocations. The correlation between in-field performance along the c-axis and microstructure of (Gd,Y)BCO film with a high level of Zr addition is discussed.

Superconducting transition width (ΔT c) characteristics of 25 mol% Zr-added (Gd, Y)Ba2Cu3O7−δ superconductor tapes with high in-field critical current density at 30 K

The superconducting transition width (∆T c) characteristics of REBa2Cu3O7−δ (REBCO and RE = Gd, Y) superconductor tapes with Zr content of 25 mol% with high lift factor (ratio of critical current density (J c) at 30 K, 3 T (B||c) to the J c at 77 K, 0 T) has been determined. In this work, heavily doped (Gd, Y)Ba2Cu3O7−δ superconductor tapes with 25 mol% Zr addition were fabricated by metal organic chemical vapor deposition using a reel-to reel process. The optimal chemical composition range of (Gd, Y)Ba2Cu3O7−δ superconductor tapes with Zr content of 25 mol% to achieve critical current densities above 3.5 MA cm−2 at 77 K in zero applied magnetic field has been determined. A superconducting transition width (∆T c) as narrow as 0.4 K and an onset critical transition temperature (T c-onset) as high as 92 K were obtained in the 25 mol% Zr-added (Gd, Y)BaCuO superconductor tapes. Based on the mapped compositional phase diagram of the ∆Tc and lift factor, ∆T c in the range of 0.7–0.9 K is observed in 25 mol% Zr-added (Gd, Y)BaCuO superconductor tapes with a high lift factor.

Broad Temperature Pinning Study of 15 mol.% Zr-Added (Gd, Y)–Ba–Cu–O MOCVD Coated Conductors

BaZrO3 (BZO) nanocolumns have long been shown to be very effective for raising the pinning force Fp of REBa2Cu3Ox (REBCO, where RE = rare earth) films at high temperatures and recently at low temperatures too. We have successfully incorporated a high density of BZO nanorods into metal organic chemical vapor deposited (MOCVD) REBCO coated conductors via Zr addition. We found that, compared to the 7.5% Zr-added coated conductor, dense BZO nanorod arrays in the 15% Zr-added conductor are effective over the whole temperature range from 77 K down to 4.2 K. We attribute the substantially enhanced Jc at 30 K to the weak uncorrelated pinning as well as the strong correlated pinning. Meanwhile, by tripling the REBCO layer thickness to ~2.8 μm, the engineering critical current density Jc at 30 K exceeds Jc of optimized Nb-Ti wires at 4.2 K.