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The flux pinning and other superconducting properties of the Y-Ba-Cu-O films doped with BaZr[O.sub.3] (BZO) nanoparticles prepared by multilayer and single target methods are explained.

The incorporation of various nanoparticulate flux pinning centers in the Y[Ba.sub.2][Cu.sub.3][O.sub.7-[delta]] films is described. The study shows that such incorporation helps in improving the in-field performance of these films.

The ultrasonic force microscopy (UFM) technique is employed for imaging of the nanoparticles present in the interior of the Y[Ba.sub.2][Cu.sub.3]pO.sub.7-x] (YBCO) films. The method also helps in providing high resolution images of the screw dislocation induced terraces present in the film.

The analysis of the transport and magnetic properties is employed for the characterization of the individual filaments in a multifilamentary YBCO coated conductor. The results show that the values of the filament critical current and the n-factor vary largely with the filament.

The study describes a newly devised hall probe system, which is used for studying the AC transport current distribution in the YBCO coated conductors at different frequencies up to 700 Hz. The sensors are found to be very advantageous because of its sensitivity, low cost and versatility.

Several studies are conducted to measure the local current transport and the current sharing between different filaments in striated coated YBCO conductors with artificial defects. The local current crowding is found to be the main cause of the dissipation of the current in these conductors.

Investigating the peak shape of the Y(3d) photoelectron peak in YBCO thin films are different compared to bulk YBCO specimens is discussed. The XPS photoelectron peaks and cationic concentration profiles of several thin film superconductors have been compared.

Having investigated the variation of Q (sub h) with d for various striated thin YBCO films is discussed. It is concluded that having computed the dependence of N on the quantity [H (sub m)/H (sub d)] within a practical range of interest.

The development of nickel alloy substrates for Y-Ba-Cu-O coated conductor applications is described.

Investigating the (Gd0.9Er0.2)(sub 2) O3 buffer layer, which matches 100% with superconducting layer, coated on RABiTS Ni substrate by using a sol-gel method is discussed. It is concluded that the different thickness of buffer layers and superconducting layer tried to the thickness effect on superconducting properties is shown.

Near-field scanning microwave microscopy (NSMM) provides a unique nondestructive approach for detection of local dissipation with high sensitivity and high spatial resolution. With recently improved NSMM probes of spatial resolution of up to 400 nm (\sim 10^-6 wavelength), detection of dissipation was achieved on YBCO microbridges at currents more than three orders of magnitude below the Jc(T). In this work, we report characterization of the dynamic behavior of low-level dissipation at the grain boundary of YBa2Cu3O7-\delta microbridges as function of time and applied electrical current. On higher-angle grain boundary, the dissipation develops rapidly with increasing current and shows approximately linear dependence on current. On lower-angle grain boundary, nonlinear features were observed and attributed to bi-modal pattern of dissipation evolution of nucleation of isolated hot spots and their evolution. Comparison with the similar NSMM+IV measurement made on the “bulk” part of the same YBa2Cu3O7-\delta microbridges on a reduced temperature scale shows higher dissipation on the grain boundary can be mostly attributed to the lower Tc values on grain boundaries. [ABSTRACT FROM AUTHOR]

We have studied the effects of localized defects in the YBCO coated conductors on the critical current. The artificial defects were introduced into 4, 10 and 12 mm wide tapes as cuts of various lengths made either by laser ablation or mechanical means. Transport measurements were carried out in an external variable magnetic field to obtain the I-V characteristics of the damaged areas. The distribution of the magnetic field in the vicinity of the defects has been mapped as well. The reduction of the critical current by the defects, with and without an external DC magnetic field are discussed and compared with existing theories. A criterion for determining the critical current in the area containing a defect is suggested. [ABSTRACT FROM AUTHOR]

We will discuss how stability and speed of normal zone propagation in YBCO-coated conductors is affected by interfacial resistance between the superconducting film and the stabilizer. Our numerical simulation has shown that the increased interfacial resistance substantially increases speed of normal zone propagation and decreases the stability margins. Optimization of the value of the resistance may lead to a better compromise between stability and quench protection requirements than what is found in currently manufactured coated conductors. [ABSTRACT FROM AUTHOR]

When grown on miscut SrTiO3 substrates, significant microstructural changes are observed in BaZrO3-doped YBa2Cu3O7-x thin films when compared to those on non-vicinal substrates. Scanning Electron Microscopy indicates a surface morphology strongly influenced by the vicinal angle, and an accumulation of BaZrO3 particles is observed near the step edges. Cross-sectional Transmission Electron Microscopy reveals that while the columnar formations of BaZrO3 rods typically seen on non-vicinal substrates are present, a significant increase in planar defects in a 100 vicinal film are observed. The effects observed with increasing miscut angle indicate that the modulated surface provided by the vicinal substrate influences the crystalline quality of the YBCO matrix and BZO columnar formation through the thickness of the film. [ABSTRACT FROM AUTHOR]

The critical current density (Jc) of YBa2Cu3O7-z films doped with varying flux pinning nanoparticle additions was systematically studied, for applied magnetic fields of H = 0-9 T and operation temperatures T = 20-77 K. Films were prepared with pulsed laser deposition by (M/YBCO)N multilayer or (YBCO)1-xMx single-target methods, for different M phases including Y2O3, Y2BaCuO5 (Y211) green-phase, and BaZrO3. Very significant differences of Jc(H//c, 20 - 77 K) were measured for optimized M phase additions, that are difficult to model or predict at present. Multilayer films with Y211 and Y2O3 nanoparticle additions had the highest Jc(20 - 77K) for H < 4 T, and YBCO+BZO-nanorod samples had the strongest Jc(H) for H > 4 T and 65-77 K, however not for T < 50 K. Seemingly unusual Jc(H, T) properties were measured for (BZO/YBCO)N multilayer films when compared to YBCO and other doped films; Jc(H) was almost the same as YBCO at 77 K, however at 30 K Jc(H > 2 T) had the strongest properties increasing 70% compared to YBCO+nanoaddition films and increasing 400% compared to YBCO. [ABSTRACT FROM AUTHOR]

A special YBa2Cu3O7-x (YBCO) target with a thin sector of second phase material, in this case either Y2BaCuO5 (Y211) or BaSnO3 (BSO), was used to deposit YBCO films with non-layered nanoparticles on single crystal LaAlO3 and biaxially textured Ni-S at.% W substrates buffered with CeO2 and YSZ layers(coated conductors). Although identical processing conditions were used, TEM images indicated that random Y211 nanoparticles in the case of YBCO+Y211, and evenly spaced BSO nanocolumns iii the case of YBCO+BSO, form in the YBCO films. While YBCO plane buckling was observed at many places in the case of YBCO+Y211, a high density of stacking faults and dislocations were observed in the case of YBCO+BSO near the BSO columns. In transport critical current density (Jo) angular dependence measurements, the absence of nanocolumns in YBCO+Y211 films resulted in the absence of a peak at 0°, J(H//e), in Jc vs. θ plots, as compared to a clear peak at 0° observed in YBCO+BSO films with the nanocolumns. The in-field J measurements indicated small low-field Jc enhancements at 77 K in YBCO+Y211 films but more than an order of magnitude improvement in high-field Jc in YBCO+BSO films due to the differences in the microstructures. [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]

Nanoparticle dispersions of various phases were added to YBa2Cu3O7-x (YBCO or 123) thin films by multilayer pulsed laser deposition, to determine their effect on flux pinning. The different pinning materials examined include Y2BaCuO2 (Y211 or green-phase), La2BaCuO2 (La211 or brown-phase), Y2O3, CeO2, and MgO, with lattice constant mismatches varying from 0.5% to 12% with respect to YBCO. Y211 and Y2O3 provided significant pinning increases at temperatures of 65 K and 77 K, however other phases provided enhancements only at 65 K (for CeO2 and La211) for limited range of applied field strengths. An interesting correlation between Tc transition widths and pinning strengths was observed. The additions produced markedly different nanoparticle and film microstructures, as well as superconducting properties. [ABSTRACT FROM AUTHOR]

A comparison study is given of a typical superconducting YBa2Cu3O7-d (Y123) film and a Y123 film containing a nonsuperconducting Y2BaCuO5 (Y211) phase nanoparticulate dispersion. The inclusion of the second phase nanoparticulates was for the express purpose of increasing superconducting film's magnetic pinning strength with the resultant improved in-field critical current density. LaAlO3 substrates were used and the Y123 and Y211 nanoparticulates were grown by pulsed laser deposition (PLD). The Y211 nanoparticulate dispersion in the Y123 resulted from multiple consecutive depositions by PLD of the respective targets. The Y123 phase maintained excellent epitaxy with high in-plane orientation with and without the Y211 inclusions. With the Y211 additions, the critical current densities of the films increased significantly in applied magnetic fields as compared to the high quality Y123 film with no Y211 additions. [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]

The possibility of a substantial reduction of weight and size of electrical generators is the main incentive behind the effort to develop superconducting armature windings based on Y1Ba2Cu3O6+x (YBCO) coated conductors in the form of wide tapes with large aspect ratio. The main obstacle to the application of coated superconductors in stator windings is the large losses incurred due to the ac magnetic field produced by the rotor's dc coils of the field windings. In the range of frequencies typical for aircraft generators, the hysteretic losses in wide tapes are unacceptably high. They can be reduced by dividing the YBCO layer into multiple filaments separated by non-superconducting barriers. However, the lack of current sharing between the filaments makes the conductor vulnerable to the localized defects, so that a single blockage can impede the flow of transport current through the whole length of a given filament. We present estimates of reliability as well as the magnetization losses in multiply connected superconductors. In this type of superconducting tape, a sparse network of superconducting bridges, which allows for current sharing, connects the filaments. The trade-off between the different types of losses and the connectivity requirement imposes restrictions on the number of filaments and properties of the network of bridges. [ABSTRACT FROM AUTHOR]

To evaluate possible flux pinning enhancement in YBa2Cu3O7-x (Y123) films due to partial rare-earth ion substitutions, Ce and Tb doping are studied. Bulk ceramic targets of varying compositions (Y1-xRExBa2Cu3O7-x) were made with several doping levels (x = 0.00 1 to 0.1, RE = Ce or Tb) by using regular solid-state reaction and sintering procedures. These targets were used to deposit Ce and Tb doped YBCO films onto SrTiO3 single crystal substrates by pulsed laser ablation. Doped YBCO films were characterized for Tc, magnetic field dependence of Jc (at 77 K), microstructure, and other properties. The results are compared to undoped YBCO films processed in similar manner. [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]

One of the methods to reduce magnetization loss of YBCO coated conductors in a perpendicular magnetic field is subdividing the YBCO layer into filaments and twisting them as a whole. A 10 mm wide multifilamentary YBCO coated conductor with 200 μm wide filaments was prepared by striation using the laser ablation technique. The number of filaments was 40. The sample length was varied from 100 mm to 25 mm, and their magnetization loss was measured at various frequencies. The measured magnetization losses were scaled using sample length, frequency, and field amplitude. This clarifies the magnetization loss characteristics of multifilamentary YBCO coated conductors and obtains empirical expressions for the magnetization loss. The measured loss was compared with the loss calculated numerically using a two dimensional FEM model. The experimentally confirmed effect of striation to reduce the magnetization loss was compared with theoretical predictions. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y[sub 1]Ba[sub 2]Cu[sub 3]O[sub 7-x] thin films were intentionally created of varying quality. The films were deposited on LaAlO[sub 3] by pulsed laser deposition with J[sub c] values ranging from poorly conducting up to several MA/cm². Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film quality. A potential correlation may also exist with the Cu(2p)/Ba(3d) ratio indicating an interrelationship to the FWHM of the Y(3d) peak. Film quality was determined by current transport, resistive T[sub c], and AC magnetic susceptibility measurements. [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]

YBa[sub 2]Cu[sub 3]O[sub 7-δ] and YbBa[sub 2]Cu[sub 3]O[sub 7-δ] layers were coated by sol-gel and PLD on Gd[sub 1.91]Er[sub 0.09]O[sub 3] (100% lattice match with Y- and Yb-123) textured buffer layer on Ni substrates. Different thickness of buffer layers and superconducting layer were tried to see the thickness effect on superconducting properties. Buffer layers were prepared with different lattice parameters for Y-123 and Yb-123. Coated conductors were characterized by means of XRD, ESEM and T[sub c] and J[sub c] measurement. Since the perfect lattice match can be achieved between buffer layer and superconducting layer, texture of superconducting film was improved, and consequently critical current density of Y- and Yb-123 were improved. [ABSTRACT FROM AUTHOR]