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

Supercond. Sci. Technol.

et al. 2020

Self Cite

The critical current and pinning mechanisms at 4.2 K have been studied over a magnetic field range of 0-14 T for Zr-added (0, 5 and 15 mol.%) REBa 2 Cu 3 O 7-x (REBCO and RE = rare earth) coated conductors fabricated by advanced metal organic chemical vapor deposition (A-MOCVD). It is found that the (Ba + Zr)/Cu content in Zr-added (5 and 15 mol.%) REBCO affects the critical current at 77 K, 0 T as well as density, continuity and shape of BaZrO 3 (BZO) self-assembled nanocolumns and RE 2 O 3 in-plane precipitates that significantly enhance the pinning force density Fp(H) as well as isotropic pinning landscape at 4.2 K. In addition to bell-shape dependence of critical current density, J c , at 4.2 K with (Ba + Zr)/Cu content we observed an unusual Fp(H) behavior correlated to particular type of pinning centers, morphology and distribution that have been revealed by TEM microstructure analysis. By fitting the Dew-Hughes equation of the pinning force density Fp(H) at 4.2 K we extract the scaling behaviors of the Fp(H) associated with the competition of pinning mechanisms driven by vertically-aligned BZO nanorods and in-plane RE 2 O 3 pinning defects. This result sheds light on approaches towards interactive control of strong and isotropic pinning centers in Zr-added REBa 2 Cu 3 O 7-x (REBCO and RE = rare earth) coated conductors, and especially understanding the correlation between microstructural characteristics and vortex pinning mechanisms at 4.2 K in high magnetic fields.

Section: Resultssupporting

confidence: 92%

In-field critical current and pinning mechanisms at 4.2 K of Zr-added REBCO coated conductors

Galstyan

Pratap

Supercond. Sci. Technol.

et al. 2020

Self Cite

“…We have reported earlier that the same metric, (Ba + Zr)/Cu, has a considerable effect on c-axis lattice mismatch between BZO and REBCO [48,61,63]. Multiple studies have reported presence of dense arrays of REBCO 124/248 type, 223 and other stacking faults [54,[83][84][85][86][87][88][89][90][91], and we have regularly observed the same features, as can also be seen in figure 2(d). One can readily envision a mismatch strain accommodation between c-axis of BZO and REBCO by inserting extra Cu-O planes to form 124-type defect at regular intervals in REBCO matrix to minimize mismatch between REBCO and BZO along the c-axis.…”

Section: In-plane Strain Accommodationsupporting

confidence: 84%

New insight into strain and composition of BaZrO₃ nanorods in REBCO superconductor

Supercond. Sci. Technol.

Jeong

Yun

et al. 2021

Self Cite

We report on strain and composition effects associated with growth of self-assembled BaZrO 3 (BZO) nanorods in REBa 2 Cu 3 O 7−δ (REBCO) superconductors (RE = rare earth = Y and Gd), which have a profound effect on flux pinning and in-field critical current performance. The a-b plane mismatch between BZO and REBCO is never fully coherently accommodated. Instead, the nanorods always assume a size at least one unit cell smaller than the corresponding 'hole' in the REBCO matrix, thus providing deep minima of in-plane mismatch strain. Next, we show that the nominal BZO nanorods are in fact solid solution Ba 2+ (Zr 4+ 1−z RE 3+ z )O 3−δ perovskite, thus strongly affecting the stoichiometry and relative amounts of REBCO and BZO. We demonstrate that by varying only the Ba content in the nominal composition of 15 mol.% BZO + REBCO, the unit cell density of BZO can be tuned from 5% to 23%, and the linear density of RE 2 O 3 (REO) precipitates from 18 to 1 µm −1 . The results explain the wide range of pinning performances observed for the same nominal amount of Zr addition and provide insight into the mechanisms behind the complex phenomenon of growth of nanorods by self-assembly in REBCO superconductors.

“…The average diameter and spacing of the BZO nanorods was found to be ~3.5 and 17.5 nm, respectively, which is consistent with that observed before in 2 μm thick films processed in A-MOCVD 23 . It has been established that long continuous and small diameter BZO nanorods that permeate the whole film contribute to strong pinning and high lift factor in critical current 12–14,16,23 . Such dependence of in-field behavior on nanorod morphology has also been reported in 27 .…”

Section: Resultsmentioning

confidence: 99%

“…Remarkable progress has been made in improving the in-field performance by thorough understanding of BZO nanorod self-assembly process and its effect on in-field performance using MOCVD. One particular aspect of interest was maximizing the lift factor (LF), defined as the ratio of I c at desired temperature/field and I c value at 77 K, self-field itself 12–15 . Extensive optimization of the REBCO-BZO system has been done using MOCVD, in terms of dopant concentration, film microstructure, growth conditions and composition to achieve high in-field performance 13,16–18 .…”

Section: Introductionmentioning

confidence: 99%

Over 15 MA/cm2 of critical current density in 4.8 µm thick, Zr-doped (Gd,Y)Ba2Cu3Ox superconductor at 30 K, 3T

Pratap

et al. 2018

Sci Rep

Self Cite

An Advanced MOCVD (A-MOCVD) reactor was used to deposit 4.8 µm thick (Gd,Y)BaCuO tapes with 15 mol% Zr addition in a single pass. A record-high critical current density (Jc) of 15.11 MA/cm2 has been measured over a bridge at 30 K, 3T, corresponding to an equivalent (Ic) value of 8705 A/12 mm width. This corresponds to a lift factor in critical current of ~11 which is the highest ever reported to the best of author’s knowledge. The measured critical current densities at 3T (B||c) and 30, 40 and 50 K, respectively, are 15.11, 9.70 and 6.26 MA/cm2, corresponding to equivalent Ic values of 8705, 5586 and 3606 A/12 mm and engineering current densities (Je) of 7068, 4535 and 2928 A/mm2. The engineering current density (Je) at 40 K, 3T is 7 times higher than that of the commercial HTS tapes available with 7.5 mol% Zr addition. Such record-high performance in thick films (>1 µm) is a clear demonstration that growing thick REBCO films with high critical current density (Jc) is possible, contrary to the usual findings of strong Jc degradation with film thickness. This achievement was possible due to a combination of strong temperature control and uniform laminar flow achieved in the A-MOCVD system, coupled with optimization of BaZrO3 nanorod growth parameters.