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The thickness dependence of critical current density (Jc) has been investigated in YBa2Cu3O7-x films with BaZrO3 (BZO) nanorods (YBCO/BZO) aligned along the film normal. With the presence of linear defects in the YBCO/BZO films, the thickness dependence of Jc becomes negligible at self field and weak applied magnetic field (H), suggesting these linear defects playing a key role to the elimination of the thickness dependence of Jc. The effect of temperature (T) and H on Jc thickness dependence have been investigated and comparisons have been made between YBCO and YBCO/BZO samples. Since BZO nanorods alignment is greatly influenced by growth temperature, the quantitative difference in terms of nanorod's density and average length is reflected on Jc angular dependence of H and Jc thickness dependence as thermally assisted flux motion (TAFM) becomes important above a threshold H determined by the BZO nanorod density. With further increasing H, a monotonically increasing Jc vs. thickness trend was observed in YBCO/BZO films, in contrast to an opposite trend when collective pinning is dominant. This result suggests the thickness dependence of Jc is dictated by the microstructure and hence pinning mechanism in YBCO films. [ABSTRACT FROM AUTHOR]

Multifilamentary coated conductor (MFCC) samples with patterned links have been studied using transport and scanning laser microscopy (SLM) techniques. Striation patterns are fashioned to define multiple filaments with discretely placed superconducting (SC) links between the filaments for current sharing and redistribution. After initial measurements, an artificial incision is made on a filament to mimic a disabled filament. The changes in global and local current transport characteristics are noted for in terms of the redistribution of current flow and the modification of local dissipation. Our results show that the patterned links between filaments play a vital role in redistributing current and encouraging current sharing. We find that the main factors in limiting the current-carrying capability of MFCC samples are local current density increases, which we call “current crowding.” The susceptible areas for current crowding are several: (1) filaments adjacent to the disabled ones, since the intact filaments have to carry extra current, (2) the links where current redistribution occurs, and (3) the partially blocked filament. [ABSTRACT FROM AUTHOR]

The superconducting properties of YBa2Cu3O7-δ (YBCO or 123) thin films doped with BaZrO3 (BZO) nanopartides by multilayer and single-target methods were studied and compared. Thin films of 123 + BZO were processed by pulsed laser deposition on LaA1O3 and SrTiO3 single crystal substrates. Multilayer (BZO0.6 nm-1.4/12315nm)19 structures were grown by alternating deposition from 123 and BZO targets, and BZO additions of 0–2 Vol% were deposited using (1231-xBZOx) single-targets. The multilayer and single-target methods of BZO addition caused significant differences of superconducting transition temperatures (Tc) measured by AC susceptibility, and critical current densities (Jc) measured by both magnetic and transport methods as a function of temperature (T), applied magnetic field (H) and angle of H field incidence (θ). Single-target films had almost linear decrease of Tc and self-field Jc with BZO vol% addition, and compared to multilayer films had lower Jc (77 K, H < 4 T) however had improved high-field properties for Jc (77 K, H > 4 T). Multilayer films had almost no decrease of Tc and self-field Jc for high BZO additions up to 10 Vol% and very strong peak of Jc(H//ab in — plane) and constant and high Jc(H,0 < θ < 80°). Single-target BZO-2 Vol% films had slightly enhanced Jc (H//c — axis), consistent with results by other authors. [ABSTRACT FROM AUTHOR]

Nanoparticles present in the interior of YBa2Cu3O7-x (YBCO) films were successfully imaged for the first time by using an ultrasonic force microscope (UFM), which can also operate as a conventional atomic force microscope (AFM). Nanoparticles of Y2BaCuO5 and BaSnO3 were introduced into YBCO films using pulsed laser ablation to improve critical current density via enhanced flux pinning. The scanning speed and ultrasonic frequencies in the range of 300–500 kHz were optimized for each sample such that the nanometer sized particles on the surface as well as from the film interior can be imaged with good contrast and resolution. UFM and AFM scans taken of the same locations were compared to show the advantages of using UFM over AFM. We demonstrate that UFM can be used nondestructively to both characterize the interior nanoparticles introduced in YBCO films and provide high resolution images of the screw dislocation induced terraces present in the films. [ABSTRACT FROM AUTHOR]

Multifilamentary YBCO coated conductor with fishnet striation pattern is investigated by transport measurements and scanning laser microscopy (SLM). Each filament is clearly visible in SLM images, and higher current flows along the edges of filaments. After initial measurements, an incision is made to disable two filaments and to investigate the changes in the current transport, the current sharing, and the dissipation patterns. Current sharing and redistribution are clearly observed among the filaments and at the weak links. We find that the dissipation is mainly caused by local current crowding. Since the current is to be shared among intact filaments, the most impacted area is the filaments closer to the disabled ones which have to carry higher current. The other susceptible area is the weak links where the current redistributes and the increased current density is expected. [ABSTRACT FROM AUTHOR]

Striation of wide YBCO coated conductor tapes is necessary to reduce the hysteresis losses. However, the processes used to striate the films may adversely affect the overall critical current of the tape not only by simple removal of superconducting material, but by introducing additional defects. We studied the transport properties of individual filaments of a filamentary YBCO tape on Hastelloy substrate striated by laser ablation. The tape consisted of 24 parallel filaments 0.5 mm wide, covered by thin Ag layer. I–V curves on 9 cm long filament sections as well as the changes of the critical current along the filament were measured at 77 K in magnetic fields up to 70 mT. 8 of 24 filaments were experimentally characterized by the mean value of the critical current and the associated n-value. The best filament had a critical current of ∼7 A at 1 microvolt/cm and B = 0. [ABSTRACT FROM AUTHOR]

The distributions of dc transport current in a copper stabilized mono-core YBCO coated conductor sample were compared with that of sinusoidal ac transport current, i(t) = Io · sin(wt), with frequencies up to 700 Hz. The current distribution was determined from the measurement of the magnetic field produced by the transport current using a small active area Hall probe. The ac magnetic field component perpendicular to the surface of the tape was measured to determine its variation across the tape. A triggering Data AcQuisition (DAQ) system, which had a capability of sampling frequency of up to 200 kHz, based on DAQ measuring cards was used. The current distribution at various phases within one ac transport current cycle for different frequency was studied. The change in frequency from ∼0 Hz up to 40 Hz had only a minor effect on the current distribution at any of the studied phases and the current distribution is practically the same as the one in dc regime. [ABSTRACT FROM AUTHOR]

Architectural design improvements, such as filamentation, to YBa2 Cu3 O7-x (YBCO) coated conductors can result in a more ac-tolerant version of the conductor. However, finely made striations in the conductor make filament breakage more probable. In this case, weakly linking the filaments can enable current sharing among the filaments of striated coated conductors while maintaining reduced hysteretic losses. Data is presented for a YBCO sample divided into superconducting filaments separated such that the transverse critical current density of the striation is significantly less than the longitudinal critical current density along the filaments. A LAO substrate was physically scribed with parallel incisions to adversely affect the subsequent epitaxial growth of the YBCO layer between the striations. Vibrating sample magnetometry measurements verified a reduction in hysteretic loss compared to a control sample of epitaxially grown YBCO on an unscribed LAO substrate. Since filamentation requires a twist in the conductor for practical applications, a discussion is also given outlining an alternate means of accomplishing this by placing a twist in the coated conductor architecture itself. [ABSTRACT FROM AUTHOR]

In this paper, we are reporting a dielectric oxide buffer Ba2 YNbO6 (BYNO) and its performance on various substrates for a potential buffer layer for the growth of YBa2Cu3O7-x (YBCO) coated conductors. Ba2YNbO6 is a moderate dielectric. Using pulsed laser deposition, epitaxial BYNO films were grown at 850° C with an oxygen pressure of 200 mTorr on single crystal MgO (100) substrate and ion beam assisted sputter deposited MgO buffered hastelloy metal substrates. The surface morphology of the BYNO films reveals out growths even though the average surface roughness is only 2-8 nm. The texture of BYNO films is ∼ 8° and thickness of these layers ∼ 100 nm on metal substrates. Highly c-axis oriented YBCO films were deposited on BYNO buffered substrates. Critical transition temperatures (Tc0) determined from electrical transport measurements vary between 88-89 K and corresponding critical current densities (Jc) ranging from 0.5-1 MA/cm² at 77 K. [ABSTRACT FROM AUTHOR]

AC losses for striped and unstriped YBCO coated conductors are presented. The loss for a sample subdivided into 10 filaments is shown to he reduced by the expected factor of 10. Various concepts for introducing strand twisting are investigated, and some estimates are given for their superconductive filling factors and the resulting twisting-induced strain. Additionally, the concept of winding induced effective twist is described, and the effective induced twist pitch is shown to be approximately two times the length of the winding. The influence of end-soldering of the strands is described, and simple estimates of the coupling losses are given for a striped strand with soldered ends in conjunction with an effective induced twist. [ABSTRACT FROM AUTHOR]

An YBCO coated conductor with a zipper pattern striation is investigated by scanning laser microscopy (SLM). The distribution of transport current deduced from the VTSLM images shows that striations act as artificial harriers forcing the current to flow around them. Current sharing and redistribution are observed at the zipper area. We find the major dissipation mechanism in the sample in the superconducting state to be the current crowding at bottleneck areas. The bottleneck seems to be caused by the disabled filaments at and around the zipper area. Some filaments show the dissipation away from the zipper area. In general, we find that the lower Jc* areas have lower Tc* and high δVm, which we consider as a sign of the current crowding. For the first time, we have demonstrated that there is a high temperature signature of the lower Jc* (high dissipation) area and VTSLM can detect the signature. [ABSTRACT FROM AUTHOR]

YBa2Cu3O7-δ high temperature superconductors can maintain fairly high critical current densities (Jc) with increasing magnetic field. This in-field performance can be further improved upon by incorporating nanoparticulate magnetic flux pinning centers into the superconductors. This short paper briefly discusses and compares recent efforts by the U.S. Air Force Research Laboratory to incorporate insulating nanoparticles into the YBCO superconducting thin films by pulsed laser deposition. [ABSTRACT FROM AUTHOR]