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An elastic strain model has been applied in an effort to understand the effect of the lattice strain on the diameter of the BaZrO3 (BZO) nanorods self-assembled into aligned arrays along the c-axis in BZO-doped epitaxial YBa2Cu3O7−δ (YBCO) thin films. The calculated elastic energy of the strained BZO/YBCO composite lattice suggests that the diameter of the nanorods is approximately independent of the doping concentration of BZO as long as the density of the nanorods is sufficiently large. An experimental confirmation was carried out using transmission electron microscopy on YBCO thin films with BZO doping varying from 2% to 6% volume concentration. The diameter of the BZO nanorods was indeed found to be approximately constant in the range of 5.2–5.9 nm. The increase of the doping concentration therefore simply leads to an increase of the nanorod density, which links directly to the matching field of the effective pinning and is consistent with the transport Jc results measured for these samples.

We present the complete superconducting upper critical field (Hc2)—temperature (T) diagram of FeTeS films measured at three crystalline orientations (H ∥ c, 45° and ab). We find that Hc2 is almost isotropic in magnetic field orientation with μ0Hc2(T = 0) ~ 30 T and a transition temperature of Tc ~ 7 K. A small but clear Hc2 angular anisotropy is observed, with a crossover around T = 0.7Tc, from Hc2(∥ c) 0.7Tc to Hc2(∥ c) > Hc2(∥ ab) for T < 0.7Tc. This change in the anisotropy is similar to that observed in FeTeS and FeTeSe single crystals but occurs at a higher T/Tc for our film. We analyze the Hc2(T) in terms of pair-breaking mechanisms and two-band superconductor theory. Understanding the inversion of Hc2 opens the possibility to adjust the effective anisotropy of superconductors for different applications.

We investigated a set of oxygen-deficient R Ba 2 Cu 3 O 7 - x (x0.3) ceramic samples with Raman spectroscopy under resonant conditions for the defect-induced Cu-O chain related modes at 230 and 600 cm - 1 . Emphasis was laidon the frequency and intensity of the modes for different rare-earth atoms, and especially on their dependence under illumination. The modes display photoinduced bleaching for all R, including the nonsuperconducting R=Pr. The dynamics of their bleaching following a temperature quench indicates similar complex relaxation processes for all samples, A simple stretched exponential with a common β = 0.36′0.04 and a distribution of time constants ranging from 50 to 1400 s describes our data well. We discuss our results in connection to photoinduced chain-oxygen ordering in oxygen-deficient superconductors.

We report on the scaling of transport properties around the vortex melting in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ oriented-twin single crystals in applied magnetic fields between 1 T and 18 T. We find that for the whole measured field range the linear resistivity scales as $\ensuremath{\rho}(t,\ensuremath{\theta})\ensuremath{\sim}{t}^{\mathrm{sy}}{\mathcal{F}}_{\ifmmode\pm\else\textpm\fi{}}(\mathrm{sin}(\ensuremath{\theta}{)t}^{\ensuremath{-}\mathrm{sx}}),$ with $t=|T\ensuremath{-}{T}_{\mathrm{BG}}|$ and $\ensuremath{\theta}$ the angle between planar defects and the magnetic field. The scaling is valid only for angles where the transition temperature ${T}_{\mathrm{BG}}(\ensuremath{\theta})$ shows a cusp. The critical exponents $\mathrm{sx}$ and $\mathrm{sy}$ are in agreement with the values predicted by Lidmar and Wallin [Europhys. Lett. 47, 494 (1999)] only at magnetic fields below 4 T. A change in the value of $\mathrm{sx}$ from $sx=1\ifmmode\pm\else\textpm\fi{}0.2$ to $sx=3\ifmmode\pm\else\textpm\fi{}0.2$ at around ${H}^{\mathrm{cr}}\ensuremath{\approx}4 \mathrm{T}$ when the magnetic field is increased is responsible for changes in the shape of the ${T}_{\mathrm{BG}}(\ensuremath{\theta})$ curve and in the dependence of the linear dissipation on temperature and angle. The results strongly suggest the existence of a different vortex glassy phase in twinned crystals compared to the Bose-glass state found in samples with linear defects.

We studied the effect of systematically-controlled size (22–83 nm) and density (0.1–13 × 1021 m−3) of strong pinning random BaMO3 (M=Zr, Nb, Sn) nanoparticles (NPs) by engineering of their inclusion in (Y0.77Gd0.23)Ba2Cu3Oy ((Y,Gd)BCO) coated conductors. The critical current density (Jc) gradually increases from that of pure (Y,Gd)BCO to that of 3 wt% BZO with increasing density of NPs for H || c and H || 45°. Moreover, at low/intermediate fields the films with higher densities of isotropic pinning centers show nearly isotropic angular dependence at both 77 and 65 K, indicating that a high density of spherical nanoparticles effectively pins vortices over a broad angular range. We find that the enhancement of Jc depends mainly on the density of the NPs and not on their size. The vortex melting transition (characterized by the critical exponent (s) of the resistive transition) changes, particularly at H || 45° in films with higher densities of NPs. This change is reflected in a decrease of s to a value very close to that observed for H || c, similar to that of a Bose-glass. Thus, the density and morphology of the pinning centers are important factors determining not only Jc but also the character of the solid–liquid transition.

We present linear and nonlinear electronic transport measurements as a function of magnetic field strength and orientation at different temperatures for BaCoxFe2 ? xAs2 biaxially oriented films grown on (La, Sr)(Al, Ta)O3 single crystals and determine the critical current density, melting line and upper critical field (Jc, Hm and Hc2). Unlike observations on single crystals of the same composition with similar Tc ~ 20?K and anisotropy ? ~ 2, we observe here a vortex liquid phase as a broadening of the resistive transition with increasing H. We find evidence of a high density of correlated defects that generate a very large Jc peak as a function of field orientation centered near the c-axis orientation with Jc > 1?MA??cm ? 2 at 4?K and 1?T and reduce the dissipation in the vortex liquid state along the defect direction. These studies indicate that these correlated defects could be more effective than the correlated defects found in more anisotropic cuprate superconductors.

We report here on significant improvements to the in-field and self-field critical current densities (Jc) of multilayer and single-layer YBa2Cu3O7 − x (YBCO) thick films with BaZrO3 (BZO) and Y2O3 additions. In the former case, the composite film consisted of a five-layer architecture with three YBCO layers and two Y2O3 interlayers in a total thickness of 1.8 µm. The multilayer film produced a Jc (75.6 K, self-field) of 4.3 MA cm − 2 (775 A cm − 1) and a minimum Jc (75.6 K, 1 T) of 1.0 MA cm − 2 (175 A cm − 1) over all field orientations in the maximum Lorentz force configuration. We achieved in a single-layer 2.0 µm thick film a Jc (75.6 K, self-field) of 5.2 MA cm − 2 (1010 A/cm-w) and a minimum Jc (75.6 K, 1 T) of 1.2 MA cm − 2 (234 A/cm-w) in the same measurement configuration. For both kinds of films, scanning transmission electron microscopy and transmission electron microscopy imaging were used to identify a uniformly dispersed second-phase microstructure consisting of short, tilted BZO nanorods and tilted Y2O3 nanoparticle layers. We attribute the enhanced performance of the thick YBCO films to the uniformity of the microstructure and the interaction of two different second-phase materials during film growth.

A much simplified template, i.e., two nonsuperconducting layers between the superconducting YBa2Cu3O7−δ (YBCO) and the polycrystalline metal substrate, has been developed for high-performance coated conductors by using biaxially aligned TiN as a seed layer. A combination of a thin TiN (∼10 nm by ion-beam assisted deposition) layer and an epitaxial buffer LaMnO3 layer (∼120 nm) allows us to grow epitaxial YBCO films with values of full width at half-maximum around 3.5° and 1.7° for the ϕ-scan of (103) and rocking curve of (005) YBCO, respectively. The YBCO films grown on electropolished polycrystalline Hastelloy using this two-layer template exhibited a superconducting transition temperature of 89.5 K, a critical current density of 1.2 MA/cm2 at 75.5 K, and an α value (proportional factor of critical current density Jc∼H−α) of around 0.33, indicating a high density of pinning centers and an absence of weak links.

We report significantly enhanced critical current densities (Jc) and flux pinning forces (Fp) in applied magnetic fields for YBa2Cu3O7 (YBCO) films with embedded Ba2YNbO6 (BYNO) nanorods. The films were grown by pulsed laser deposition with a target consisting of YBa2Cu3Oy with five molar per cent additions of BaNbOy and Y2O3. With this composition, deposited films were found to contain a high density of BYNO nanorods that frequently traversed the entire thickness of the film (up to 1? ?m), depending upon the deposition conditions. Enhanced Jc performance occurs primarily for applied field orientations near the c-axis of the YBCO, which is nominally along the growth direction of the BYNO nanorods. The threading nanorod density of one film of the present work was measured by plan-view transmission electron microscopy to be 710?850 nanorods??m ? 2. For approximately 1??m thick films, typical Jc(75.6?K, sf) and values were ~ 4.5?MA?cm ? 2 and 1.3?1.5?MA?cm ? 2, respectively. For a 0.5??m thick film, was achieved, and values of Fp in excess of 30 and 120?GN?m ? 3 were achieved at 75.5?K and 65?K, respectively.

We have developed Y2O3:Al2O3 (YAlO) composites to simplify the architecture of superconducting YBa2Cu3O7?x (YBCO) thick films on polycrystalline metal substrates. By implementing the use of YAlO, we have reduced the total number of non-superconducting layers between the polycrystalline metal substrate and the YBCO film from five (as in the standard architecture used by industry) to three. The YBCO films grown on this simplified platform exhibited an in-plane mosaic spread of less than 4? in full width at half-maximum, correlated pinning centered at , and an ? value (the proportionality factor of the critical current density H ? ?) of around 0.38 over the field range of 0.1?1.0?T. We believe that the excellent structural stability at high temperatures and the exceptional chemical inertness in an oxidizing environment make YAlO a good choice for use in the growth of biaxially oriented MgO and subsequent buffer and superconducting layers.

The Holy Grail for high temperature superconducting conductors is achieving high current material in a simple and cost-effective way. The current status is encouraging but even after more than twenty years of intense worldwide research, there are still many new avenues to be explored. Innovative functional oxide materials science is central to future progress. This paper discusses three key areas of our research focusing on new directions: highly tailored flux pinning using the new core pinning additives R3TaO7 and RBa2NbO6 for control of nanostructure formation; pinning using magnetic phase additives such as RFeO3 with the potential for a magnetic contribution to the flux pinning; and the use of liquid assisted growth enabling very high growth rates leading to thick films with no critical current degradation.

Higher irreversibility fields (Hirr) increase the upper bound for applications of superconductors and could expand market penetration. We present the studies in pulsed field (up to 65 T) of superconducting films on flexible metal substrates. We investigate the effect of disorder on Hirr at different field orientations for YBa2Cu3Oy and BaZrO3-nanoparticle-dispersed Y0.77Gd0.33Ba2Cu3Oy (YGdBCO+BZO). We find that Hirr is higher for YGdBCO+BZO along the c-axis and at intermediate orientations. The vortex melting transition is investigated using the resistive transition’s critical exponent. The behavior can be explained by the mixed pinning landscape from randomly distributed BZO nanoparticles and c-axis correlated disorder.

We have used an ion beam sputtered Y2O3?Al2O3 (YALO) composite to simplify the architecture of high temperature superconducting (HTS) coated conductors (CCs) based on a IBAD MgO template. By implementing YALO, we have reduced the total non-superconducting layers between the polycrystalline metal substrate and the superconducting film from five (the standard architecture) to four. Well textured (Y,Gd)Ba2Cu3O7?x ((Y, Gd)BCO) films have been successfully grown by MOCVD on this simplified template. The microstructural characterization revealed that all layers are continuous and uniform with sharp and clean interfaces. Additionally, the YALO maintained its amorphous nature after the deposition of the superconductive layer, which is a plus in terms of its efficiency as a diffusion barrier. The achievement of a self-field critical current of 230? A?cm?1 at 75.5?K is another proof of the effectiveness of YALO as a diffusion barrier and nucleation seed for the MgO. The transport properties under an applied magnetic field of MOCVD grown (Y, Gd)BCO on LMO buffered MgO/YALO/Ni-alloy are comparable with those of (Y, Gd)BCO on a standard architecture, thus demonstrating good compatibility between the simplified template with the MOCVD grown (Y, Gd)BCO. The use of a single composite YALO layer instead of individual layers of Y2O3 and Al2O3 for the large scale fabrication of HTS CCs based on IBAD MgO provides advantages such as potentially reduced cost due to the reduced number of fabrication steps.

We demonstrate coated conductors fabricated by reactive co-evaporation of YBa2Cu3Oy (YBCO) by cyclic deposition and reaction (RCE-CDR) on ion-beam-assisted-deposition- (IBAD-) textured templates simplified by the elimination of the epitaxial buffer layer. Hastelloy substrates, both polished and unpolished, were used as a starting material for the IBAD templates. Y2O3 bed layers were then deposited followed by IBAD-textured MgO and a thin homoepitaxial MgO layer. The MgO-terminated templates were used for direct deposition of YBCO by RCE-CDR. Critical current densities obtained for the undoped YBCO material are comparable to the best values measured previously with the use of LaMnO3 or SrTiO3 epitaxial buffer layers and state-of-the-art coated conductor results. The structural characterization data indicate a well oriented YBCO film with a robust template. Electrical measurements also indicate no weak links and a typical magnetic field behavior of undoped YBCO, characterized by a low density of naturally occurring strong pinning centers and correlations along the ab direction.

We present measurements of the field and angular dependence of the critical current density (Jc) and melting line made using transport and magnetization techniques for SrFe1.8Co0.2As2 (nominal composition) biaxially oriented films. At high magnetic fields the angular dependence of the melting line and Jc (for ?0H>2?T) can be successfully scaled using an anisotropic scaling with ? = 2, indicating a random-point-like pinning contribution. At lower fields, angular and field Jc dependences strongly depend on the magnetic field history. We find a hysteretic behaviour of Jc with H with higher Jc in the descending branch, similar to that attributed to magnetic pinning and granularity effects. Furthermore this allows us to tune Jc(?) such that a Jc peak along the c axis can be enhanced up to 30%. The low values of Jc measured suggest that granularity depresses Jc but does not rule out the possibility of dilute magnetic pinning.

The critical current density (Jc) of very thin YBa2Cu3O7?? (YBCO) films can approach 10?MA?cm?2 at 77?K in self-field, but for such films Jc drops sharply as the film thickness is increased. We have shown previously that this strong thickness dependence results from an enhancement of Jc near the film?substrate interface. In the present paper we investigate interfacial enhancement using laser-deposited YBCO films on NdGaO3 substrates, and find that we can adjust deposition conditions to switch the enhancement on and off. We find that the 'on' state is accompanied by a dense array of interfacial misfit dislocations, while we do not observe dislocations in films prepared in the 'off' state. This result appears to be but one of many examples in which interfacial properties of electronic film materials are profoundly affected by stress-induced defects at the film?substrate interface; however, to our knowledge the present work is the only case in which electronic properties are shown to be enhanced by such defects.

We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7?? (YBCO) films with 5?mol% BaZrO3 (BZO) and 5?mol% Y2O3 additions grown on single crystal SrTiO3 substrates by pulsed laser deposition (PLD). The results show that adding BZO+Y2O3 has reduced the thickness dependence of the self-field critical current density (Jcsf), compared to that observed in optimized YBCO films, with a significant enhancement of Jcsf in the thick film region (>2??m). The so-called 'dead layer' did not appear until the film thickness was greater than 6.4? ?m. We attribute this improvement to the additional pinning centers introduced in the bulk by the addition and a decrease in microstructure degradation with thickness. As a result, Jcsf remains as high as 2.3?MA?cm?2 in a 6.4? ?m?thick film. The combination of this high Jcsf value and the enhancement of the in-field Jc induced by the additions, which was observed in the whole thickness range, leads to a critical current per centimeter width (Ic?w) in excess of 400?A?cm?1 at 1?T and 75.5?K and 530?A?cm?1 at 3?T and 65?K under all field directions.

Metal–organic chemical vapor deposition (MOCVD) on flexible, ion beam assisted deposition MgO templates has been used to produce high critical current density (Jc) (Y,Sm)1Ba2Cu3Oy (REBCO) films suitable for use in producing practical high temperature superconducting (HTS) coated conductor wires. Thick films on tape were produced with sequential additions of 0.7 µm of REBCO via a reel-to-reel progression through a custom-designed MOCVD reactor. Multi-pass processing for thick film deposition is critically dependent upon minimizing surface secondary phase formation. Critical currents (Ics) of up to 600 A/cm width (t = 2.8 µm, Jc = 2.6 MA cm−2, 77 K, self-field) were obtained in short lengths of HTS wires. These high performance MOCVD films are characterized by closely spaced (Y,Sm)2O3 nanoparticle layers that may be tilted relative to the film normal and REBCO orientation. Small shifts in the angular dependence of Jc in low and intermediate applied magnetic fields can be associated with the tilted nanoparticle layers. Also present in these films were YCuO2 nanoplates aligned with the YBCO matrix (short dimension perpendicular to the film normal), threading dislocations, and oriented composite defects (OCDs). The latter structures consist of single or multiple a-axis oriented grains coated on each side with insulating (Y,Sm)2O3 or CuO. The OCDs formed a connected network of insulating phases by the end of the fourth pass. Subsequent attempts at adding additional layers did not increase Ic. There is an inconsistency between the measured Jc and the observed microstructural degradation that occurs with each additional layer, suggesting that previously deposited layers are improving with each repeated reactor pass. These dynamic changes suggest a role for post-processing to optimize superconducting properties of as-deposited films, addressing issues associated with reproducibility and manufacturing yield.

Addition of pyrochlore rare earth tantalate phases, RE3TaO7 (RTO, where RE = rare earth, Er, Gd and Yb) to YBa2Cu3O7?? (YBCO) is shown to vastly improve pinning, without being detrimental to the superconducting transition temperature. The closely lattice matched to RTO phase provides a lower interfacial energy with YBCO than BaZrO3 (BZO) and produces very fine (~5?nm) particles with high linearity in their self-assembly along c. Critical current densities of 0.86, 0.38?MA?cm?2 at 1 and 3?T (for fields) parallel to the c axis were recorded at 77?K in 0.5?1.0??m thick films and a transition temperature of 92?K was observed even in the highest level doped sample (8?mol%).

A study is presented on the evolution through thickness of the angular and magnetic field (H) dependence of the critical current density (Jc) for YBa2Cu3O7 films grown by the trifluoroacetate route. A clear relation between Jc at self-field (sf) and the thickness-dependent distribution of pinning centers parallel to the ab-planes is found and confirmed by microstructural analysis. Results indicate that stacking faults and their associated partial dislocations are relevant pinning centers for determining the thickness dependence of and Jc(sf), respectively, supporting the hypothesis that the thickness dependence of Jc is related to defect density.

YBa2Cu3O7−x (YBCO) thick films were grown by hybrid liquid phase epitaxy (HLPE) on (001) SrTiO3 (STO) substrates. In the presence of a 100 nm thick, 5 mol% Au-doped STO buffer, self-field critical current densities, Jcsf, at 77 K of ~2.4 MA cm−2 and critical currents, Icsf, up to 700 A (cm-width)−1 were achieved. The Jc value is virtually independent of thickness and the growth rates are very high (~1 µm min−1). From transmission electron microscopy (TEM), Y2O3 nanocloud extended defects (~100 nm in size) were identified as the pinning defects in the films. Enhanced random pinning was induced by the presence of Au in the buffer.

Textured samarium zirconate (SZO) films have been grown by reactive cosputtering directly on an ion beam assisted deposited (IBAD) MgO template, without an intermediate homoepitaxial MgO layer. The subsequent growth of 0.9 µm thick (Y,Gd)Ba2Cu3O7−δ ((Y, Gd)BCO) films by metal organic chemical vapor deposition (MOCVD) yielded well textured films with a full width at half maximum of 1.9° and 3.4° for the out-of-plane and in-plane texture, respectively. Microstructural characterizations of the SZO buffered samples revealed clean interfaces. This indicates that the SZO not only provides a diffusion barrier, but also functions as a buffer for (Y, Gd)BCO grown by MOCVD. The achievement of self-field critical current densities (Jc) of over 2 MA cm−2 at 75.5 K is another proof of the effectiveness of SZO as a buffer on the IBAD-MgO template. The in-field measurements revealed an asymmetric angular dependence of Jc and a shift of the ab-plane maxima due to the tilted nature of the template and (Y,Gd)2O3 particles existing in the (Y, Gd)BCO matrix. The present results are especially important because they demonstrate that high temperature superconducting coated conductors with simpler architecture can be fabricated using commercially viable processes.

We present a study on the angular dependence of the critical current density (Jc) of SiC-doped MgB2 tapes fabricated by powder-in tube (PIT) with stainless steel (SS) as sheath material. The microstructure and texturing of the tapes are analysed to understand the effects of the rolling degree on the superconducting properties. The microstructure is studied by x-ray diffraction and scanning electron microscopy, while Jc is measured by transport in liquid He and Ne. We found that for Si-doped tapes the alignment degree augmented with increasing deformation but tends to saturate for aspect ratios larger than 5, while the anisotropy factor JAF=Jc(90°)/Jc(0°) continued increasing for larger aspect ratios. This increase is attributed to a pinning decrease for the applied field parallel to the tape direction. Very high Jc values were obtained for Si-doped tapes, whose cores are as dense as those from wires processed using hot isostatic pressing (HIPing) by optimizing the rolling degree.

This work describes in detail the simultaneous enhancement of the upper critical field (Hc2) and the critical current density (Jc) of MgB2 bulk samples doped with nano-SiC particles, as well as single-walled and double-walled (dw) carbon nanotubes (CNTs). The magnetization properties were examined in a superconducting quantum interference device magnetometer, and four-probe transport measurements were performed using a 50T pulsed magnet to determine Hc2(T). We found that the Jc enhancement is similar in all doped samples at 5K but nano-SiC addition is more effective to improve the flux pinning in the high temperature range (T⩾20K); this improvement cannot solely be attributed to the C incorporation to the lattice but also to the presence of other types of defects (i.e., several kinds of nanoinclusions). CNTs produce a better C incorporation that is more effective to enhance Hc2 [i.e., dwCNT-doped samples reached a record Hc2(0)∼44T value for bulk MgB2]. All the Hc2(T) curves obtained for different types o...

This paper reports a study on mixed rare-earth barium–copper oxide superconducting films (Y0.67Eu0.33)Ba2Cu3O7−δ of different thicknesses grown on single-crystal SrTiO3 substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) were employed to investigate film crystallinity, surface morphology and microstructure. Critical current density in self-field as a function of film thickness and in an applied magnetic field as a function of field strength and direction were also measured. The results show high quality (Y0.67Eu0.33)Ba2Cu3O7−δ films with a smoother and denser surface morphology compared to that of pure YBa2Cu3O7−δ. A thickness-dependent self-field critical current density quantitatively similar to that of pure YBa2Cu3O7−δ was observed, which suggests that the microstructural evolution in terms of increasing surface roughness and microporosity as well as crystallinity degradation is not likely to be playing a critical role in the form of the dependence. (Y0.67Eu0.33)Ba2Cu3O7−δ films also exhibit improved magnetic field performance at low fields over a wide range of orientations in the intermediate angle region, indicating that probable additional random pinning sites were introduced by the substitution of europium in one-third of yttrium sites.

We have studied the critical current density (Jc) as a function of applied magnetic field (H) magnitude and orientation for ∼1-μm-thick YBa2Cu3O7−x films grown by pulsed laser deposition at growth temperatures (Tg) from 730to870°C. With changing Tg, alternately a high density of planar defects (YBa2Cu4Ox intergrowths) or columnar defects (Y–Cu–O nanocolumns) are introduced. These defects produce a maximum for Jc(H∼1T) parallel to the plane of the film or the film normal, respectively. For Tg⩾830°C, we present evidence of a Ba–Cu–O liquid phase during growth, which results in a dramatic change in both the microstructure of the films and magnetic field orientation dependence of Jc.

Epitaxial YXBa2Cu3O7−δ (YXBCO) thin films were deposited by pulsed laser deposition on both single crystal SrTiO3 (100) and buffered polycrystalline metal substrates, where X=0.9, 1.0, 1.1, 1.2, and 1.3. The self-field critical current density (Jc) of YXBCO exhibits the best performance at X=1.1 for the samples on both single crystal substrates and metal substrates. Epitaxial Y2O3 nanoparticles were observed in Y-rich samples (X>1.0) by X-ray diffraction and cross-sectional transmission electron microscopy. The field-dependence and angular-dependence measurements show that Y2O3 nanoparticles improve the in-field Jc performance, especially in the low field regime, without reducing self-field Jc of YBCO films.

We have grown epitaxial films of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) on single crystalline LaAlO3 substrates by a cost effective polymer-assisted deposition technique. Film crystallinity, microstructure, resistivity, magnetization, and magnetoresistance (MR) were highly dependent on the annealing temperature in the film processing. High negative MR values of −50% (at 305K) and −88% (at 250K) were observed at magnetic field of 5T, for high temperature annealed LSMO and LCMO films, respectively. These results are comparable to those for films grown by pulsed laser deposition and rf sputtering techniques.

Liquid-mediated growth of YBa2Cu3O7−x has the potential to be high rate and low cost. However, the reported critical current densities (Jc) are generally lower than for films deposited by physical vapor deposition processes. We report the deposition of thick high-Jc films (1.2MAcm−2 in self-field) on (001) SrTiO3 by high-rate hybrid liquid phase epitaxy, and show angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy.

Remarkable progress has been made in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors, and the problems of continuous processing of commercially viable tape lengths are being rapidly solved by companies around the world. However, the current carried by these tapes is presently limited to about 100A for a 1-cm-wide tape, and this is due to a rapid decrease of critical current density (Jc) as the coating thickness is increased. We have now overcome this problem by separating relatively thin YBCO layers with very thin layers of CeO2. Using this multilayer technology, we have achieved Jc values on metal substrates of up to 4.0MA∕cm2 (75K, self-field) in films as thick as 3.5μm, for an extrapolated current of 1400A∕cm width.

We present angular-dependent measurements of the critical current density (Jc) of a YBa2Cu3O7 film grown on tilted buffered Ion-Beam-Assisted-Deposition MgO metal tapes. We compare samples with the current parallel and perpendicular to the tape’s direction. In samples with the current parallel to the tape, we observe an asymmetric angular dependence of Jc and a shift of the ab-planes maxima position with the magnetic field strength. The shift is a result of the misalignment between the applied and internal magnetic fields. The misalignment effect takes place at fields lower than 3T at T=75.5K. For samples with the current perpendicular to the tape, we find an overall reduced value of Jc, the angular behavior is symmetrical, and no shift in the maxima position as a function of the magnetic field is observed. These results indicate that the effect of misalignment between the applied and internal magnetic fields must be taken into account when studying the angular dependence of Jc.

The local modification of an insulating GdBa2Cu3O6.5 thin film, made superconducting by illumination with a near-field scanning optical microscope (NSOM), is reported. A 100-nm aperture NSOM probe acts as a sub-wavelength light source of wavelength lambda(exc) = 480-650 nm, locally generating photocarriers in an otherwise insulating GdBa2-Cu3O6.5 thin film. Of the photogenerated electron-hole pairs, electrons are trapped in the crystallographic lattice, defining an electrostatic confining potential to enable the holes to move. Reflectance measurements at lambda = 1.55 microm at room temperature show that photocarriers can be induced and constrained to move on a approximately 200 nm scale for all investigated lambda(exc). Photogenerated wires present a superconducting critical temperature Tc= 12 K with a critical current density Jc = 10(4) A cm(-2). Exploiting the flexibility provided by photodoping through a NSOM probe, a junction was written by photodoping a wire with a narrow (approximately 50 nm) under-illuminated gap. The strong magnetic field modulation of the critical current provides a clear signature of the existence of a Josephson effect in the junction.

The main challenges for the success of high temperature superconducting wires, the YBa2Cu3O7 (YBCO) coated conductors (CC), are to avoid the the weak-link problem through the production of biaxially textured films, and to increase the critical current density (J c) through the introduction of large densities of appropriate defects. To that end, it is essential to understand the pinning mechanisms and their correlation with the microstructure of the CC. We first present a brief overview of the main methods currently used to produce YBCO CC, and we describe the architecture of the YBCO on IBAD fabricated at Los Alamos, summarizing the recent improvements of their structural and superconducting properties. Then, we analyze some aspects of the J c dependence on temperature and magnetic field (orientation and intensity) for the best CC available, and we compare and contrast the results with those of YBCO thin films on single crystal substrates, in order to determine if the defects controlling the pinning mechanisms are the same in both cases. Our results indicate that over large field and angular ranges J c on CC is higher than J c in thin films on SCS.