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Composite metal oxides have been extensively investigated in bulk and thin film forms because of their wide range of applications in microelectronics, magneto electronics, and optoelectronics. Metal oxides in nanocomposite form are particularly appealing as the interaction or coupling between the constituents can lead to enhanced or new functionalities. In a film-on-substrate geometry, epitaxial composite films can be created in two forms, horizontal and vertical. Nanocomposite films with a vertical architecture such as the nanopillar geometry offer numerous advantages over the conventional horizontal multilayers, such as a larger interfacial area and intrinsic heteroepitaxy in three dimensions. Moshnyaga et al. firstly showed vertical nanopillar films with a composition of (La0.7Ca0.3MnO3)1 x:(MgO)x. [3] The structural and magnetotransport properties of the La0.7Ca0.3MnO3 nanoclusters were tuned through the tensile stress originating from the MgO second phase. Zheng et al. reported vertical nanostructures consisting of magnetic spinel CoFe2O4 pillars epitaxially embedded into a ferroelectric BaTiO3 matrix. [4,8] This nanocomposite exhibited strong coupling of the ferroelectric and magnetic order parameters through the three-dimensional heteroepitaxy of the two lattices. For epitaxial metal oxide films, interfaces always play a critical role in controlling the structural and electrical properties. Both experimental and theoretical works have demonstrated the impact of lateral interface on the physical properties of either single-phase thin films or superlattices. For instance, Reyren et al. reported superconductivity in the electron gas formed at the interface between LaAlO3 and SrTiO3. [13] There have also been reports on the lateral interface effect on the physical properties of ferroelectric thin films, such as size effects, critical thickness, and strain and coupling enhanced ferroelectricity. Compared with the lateral interface, the effect of vertical interface on the physical properties of metal oxide films is profound. However, there are only a few reports because of the lack of vertical nanocomposites with ordered structures on a large scale. We have recently fabricated (BiFeO3)0.5:(Sm2O3)0.5 nanocomposite thin films, where both BiFeO3 (BFO) and Sm2O3 (SmO) phases are spontaneously self-assembled into a vertically ordered nanocolumnar structure. In this work, we demonstrate the vertical interface effect on lattice parameters, dielectric properties, and leakage current of BFO:SmO nanocomposite films. To illustrate the improved functionalities of our nanocomposites, we compare to the physical properties of pure BFO and SmO thin films. In order to reveal the microstructure of self-assembled BFO:SmO nanocomposites, plan-view and cross-sectional transmission electron microscopy (TEM) was performed. As can be seen from the plan-view TEM image (Fig. 1a), a checker-board structure is formed. In other words, an ordered alternative growth of BFO and SmO domains (marked as B and S, respectively) is self-assembled. Each of the domains has a lateral dimension of 15 nm. A low magnification bright-field cross-sectional TEM image (Fig. 1b) also shows that the BFO and SmO domains have grown alternately and vertically aligned with an average column size of 15 nm. A high resolution TEM (HRTEM) image (Fig. 1c) reveals excellent heteroepitaxial growth of the BFO and SmO nanocolumns on the STO substrate. It is interesting to note that there is a lattice matching relation along the vertical boundaries between the BFO and SmO. The matching spacing is about 1.3 nm. The corresponding fast Fourier transformed images from the areas of the BFO, SmO, and STO are shown as an insert of Figure 1c. The orientation relations of the BFO:SmO nanocomposite and the substrate are determined to be (002)BFO// (004)SmO//(002)STO and [200]BFO//[440]SmO//[200]STO, which is in accordance with the pure BFO and SmO thin films grown on STO substrates. The BFO:SmO nanocomposite thin film provides the opportunity to investigate the vertical interface effect on the physical properties of the individual BFO and SmO phases by comparison to the pure-phase films. Table 1 shows the out-of-plane lattice constants of individual BFO and SmO phases in the BFO:SmO nanocomposite. In comparison, lattice parameters of pure BFO and SmO thin films and bulk values of BFO and SmO are also included in the table. The out-of-plane lattice constant of the BFO phase in the nanocomposite is 3.905 A, compared with a value of 3.981 and 3.962 A for the pure BFO film and the bulk BFO, respectively. It C O M M U N IC A T IO N www.advmat.de

A composite layer has been successfully implemented in high temperature superconducting (HTS) coated conductors (CCs) based on ion beam assisted deposition (IBAD) MgO technology. This layer serves a dual function: a nucleation layer for the growth of high quality biaxially aligned MgO and a diffusion barrier to inhibit interdiffusion between the Ni-alloy substrate and the superconductor. The composition of the composite Y2O3-Al2O3 influences the texture and superconducting properties of YBCO films grown on STO buffered MgO/Y2O3-Al2O3/Ni-alloy. Our experimental results demonstrate that the superconducting properties of YBCO grown on STO buffered MgO/Y2O3-Al2O3/Ni-alloy are comparable with those of YBCO on standard architecture. The use of a single composite Y2O3-Al2O3 layer instead of individual layers of Y2O3 and Al2O3 for the fabrication of HTS CCs based on IBAD MgO provides advantages such as simplified architecture and potentially reduced cost due to the reduced number of fabrication steps.

High critical current densities (J{sub c}) in thick films of the Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO, {Tc}{approx}92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application-dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect-free conductor in which the grain-to-grain connectivity maintains levels of inter-grain J{sub c} that are comparable to the intra-grain J{sub c}. That is, high critical current (I{sub c}) YBCO coated conductors must contain engineered in homogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high-performance YBCO coated-conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano-engineer the microstructure for tunable superconducting wires. Multi-scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher I{sub c} wires for large-scale, commercial applicationmore » are discussed within the context of these recent advances.« less

Implementation of improved processing for BaF/sub 2/ ex situ YBCO coatings from e-beam evaporated precursors enables faster conversion with rates up to 12 /spl Aring//s and critical currents I/sub c/ at 77 K greater than 350 A/cm-width on a RABiTS template. Details of the faster processing are described and compared to an earlier slower process. A linear relation between I/sub c/ and YBCO layer thickness provides evidence of new opportunities to further improve I/sub c/.

Magneto-optical imaging, electromagnetic measurements and SEM have been used for the characterization of a monocore BSCCO tape made by oxide powder-in-tube process which had a transport J/sub c/ (77 K, 0 T) of 37 kA/cm/sup 2/. Our study evaluates the connectivity between superconducting grains and reconstructs the local current distribution at

The phase and microstructural evolution, and critical current density of (Bi,Pb)-2223/Ag tapes prepared from a variety of precursor powders have been investigated. Correlations between the reaction kinetics, the microstructure and the critical current density are developed. A mechanism for the BSCCO-2223 phase formation depending on the precursor phase assemblage is presented. Magneto-optical imaging shows that high J/sub c/ samples (J/sub c/ (77 K, 0 T) /spl sim/35 kA/cm/sup 2/) are well connected longitudinally but strongly sub-divided by longitudinal cracks. The performance of BSCCO-2223 tapes should be further improved by controlling the liquid phase to better heal the cracks.

We investigate dc-current flow in high-jc YBa2Cu3O7−δ-coated conductors by low-temperature laser scanning microscopy (LTLSM) and correlate the LTLSM response to magneto-optical imaging (MOI) and grain boundary (GB) misorientation. Because the voltage response measured by LTLSM is associated with the local electric field, while MOI shows the local magnetic field, the combination of these two techniques unambiguously shows that the dominant sources of dissipation and easy flux flow occur at and near GBs. By correlating LTLSM images to grain misorientation maps determined by electron backscatter diffraction (EBSD), we can directly observe the overloading of current paths through low-angle GBs neighboring higher-angle GBs.

Coupled magneto-optical imaging and local misorientation angle mapping have been used to demonstrate the percolative nature of supercurrent flow in YBa2Cu3O7−x(YBCO) coated conductors grown on deformation-textured Ni substrates. Barriers to current flow occur at many YBCO grain boundaries (GBs) which have propagated through the buffer layers from the underlying Ni substrate, and all Ni GBs with misorientation angles >4° initiate percolative current flow. This type of current barrier is characteristic of the conductor form and has been found to exist in samples with Jc(0 T,77 K) values >2 MA/cm2. Sharpening of the local substrate texture or improving in low-angle GB properties should lead to higher Jc values.

We employed a scanning Hall probe microscope to detect the hopping of individual vortices between pinning sites along grain boundaries in YBa2Cu3O6+δ thin films in the presence of an applied current. Detecting the motion of individual vortices allowed us to probe the current-voltage (I-V) characteristics of the grain boundary with voltage sensitivity below a femtovolt. We find a very sharp onset of dissipation with V∝In with an unprecedented high exponent of n ≈ 290 that shows essentially no dependence on temperature or grain boundary angle. Our data have no straightforward explanation within the existing grain boundary transport models.

It is indispensable to use thin films for many technological applications. This is the first report of epitaxial growth of ternary nitride AMN2 films. Epitaxial tetragonal SrTiN2 films have been successfully prepared by a chemical solution approach, polymer-assisted deposition. The structural, electrical, and optical properties of the films are also investigated.

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.

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.

Nanocomposite (BiFeO3)0.5:(Sm2O3)0.5 films were deposited on (001) oriented Nb-doped SrTiO3 substrates by pulsed laser deposition. The leakage current density versus electric field characteristics were investigated and compared with those of as-deposited and annealed pure BiFeO3 (BFO) thin films. The dominant leakage mechanisms of nanocomposite films were space-charge-limited current and Poole–Frenkle emission for positive and negative biases, respectively. The leakage current density of nanocomposite films was reduced three orders of magnitude in comparison with the as-deposited pure BFO films. The less oxygen vacancies in the BFO phase in the nanocomposite is believed to contribute to the leakage reduction.

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.

Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on (001) Nb-doped SrTiO3 (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a p-type semiconductor and formed a p-n heterojunction with an n-type semiconductor Nb-STO. The current density versus voltage (J-V) and capacitance versus voltage (C-V) characteristics of the heterojunction were investigated. A typical rectifying J-V effect was observed with a large rectifying ratio of 5×104. Reverse C-V characteristics exhibited a linear 1∕C2 versus V plot, from which a built-in potential of 0.6V was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.

A correlation has been observed between the through-thickness cation disorder level in YBa2Cu3O7 (YBCO) coated conductor films and the commonly observed falloff in layer-by-layer through-thickness critical current density (Jc) of YBCO films produced by pulsed laser deposition (PLD) on single crystal substrates. The amount of cation disorder with respect to the aggregate, c-axis-textured YBCO content was measured by Raman spectroscopy methods combined with step milling of 1.5–1.7μm thick YBCO films. For PLD YBCO films on single crystal strontium titanate, the Raman results indicate a sharp drop off in cation disorder from the substrate surface outward toward the top of the YBCO film. This drop off appears to level out in the 0.4–0.6μm range, after which the cation disorder level remains relatively constant. This trend appears to be very much like the one reported by others for the through-thickness Jc dependence of PLD YBCO on single crystal specimens. Conversely, metal-organic-deposition-produced YBCO fil...

We report on the in-plane magnetic field (H) dependence of the critical current density (Jc) in meandered and planar single grain boundaries (GBs) isolated in YBa2Cu3O7-d (YBCO) coated conductors. The Jc(H)properties of the planar GB are consistent with those previously seen in single GBs of YBCO films grown on SrTiO3 bi-crystals. In the straight boundary a characteristic flux channeling regime when H is oriented near the GB plane, associated with a reduced Jc, is seen. The meandered GB does not show vortex channeling since it is not possible for a sufficient length of vortex line to lie within it., Submitted to APL

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.

It has been well established that the critical current density Jc across grain boundaries (GBs) in high-temperature superconductors decreases exponentially with misorientation angle θ beyond ∼2°–3°. This rapid decrease is due to a suppression of the superconducting order parameter at the grain boundary, giving rise to weakly pinned Abrikosov-Josephson (AJ) vortices. Here we show that if the GB plane meanders, this exponential dependence no longer holds, permitting greatly enhanced Jc values: up to six times at 0T and four times at 1T at θ∼4°–6°. This enhancement is due to an increase in the current-carrying cross section of the GBs and the appearance of short AJ vortex segments in the GB plane, confined by the interaction with strongly pinned Abrikosov (A) vortices in the grains.

Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on conductive SrRuO3 (SRO) on (001) SrTiO3 substrates by pulsed laser deposition. A Pt/BFO/SRO capacitor was constructed by depositing a top Pt electrode. The leakage current density versus. electric field characteristics were investigated from 80to350K. It was found that the leakage mechanisms were a strong function of temperature and voltage polarity. At temperatures between 80 and 150K, space-charge-limited current was the dominant leakage mechanism for both negative and positive biases. On the other hand, at temperatures between 200 and 350K the dominant leakage mechanisms were Poole-Frenkle emission and Fowler-Nordheim tunneling for negative and positive biases, respectively.

The authors find the critical current anisotropy of a bilayer YBa2Cu3O7−δ film with different pinning structures in each layer is the sum of the anisotropy of the two individual layers, revealing that it is possible to tune the anisotropy of the composite through variation of an individual layer’s thickness and pinning structure. YBa2Cu4Ox intergrowths and Dy2O3 nanodots were the dominant pinning structures in the top and bottom layers, respectively. The bottom layer of the composite was isolated using traditional Ar+ ion milling and the top layer was isolated using a focused ion beam, allowing each layer to be studied independently.

The superconducting grain-boundary (GB) network of coated conductors (CCs) is usually assumed to be a replica of the substrate network. In this letter, we analyze IBAD and RABITS CCs, where such replica either do or do not exist. We have analyzed the effect of GB overgrowth on the critical currents by quantifying the average superconducting grain size and determining the intragrain and grain-boundary critical current densities, JcG and JcGB. We have employed a recently developed inductive methodology enabling the simultaneous determination of these three parameters. We show that the percolative JcGB may be reduced by 50% if the GB networks do not correlate, while JcG and the grain pinning properties appear unaffected.