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Experiments on quench propagation in high-current, high field High Temperature Superconducting (HTS) Cable-In-Conduit Conductors (CICCs) for fusion applications are forthcoming. Among the conductor designs to be tested, there is the ENEA slotted core proposal. In order to support the design of the samples and plan the diagnostics to be employed, a 1D multi-region thermal-hydraulic and electric model of the samples has been developed using the H4C code. After an experimental electric characterization, the model is applied to the simulation of quench propagation in the samples. The simulations show how current redistributes among the tapes and the slots. Additionally, they show that the quench protection strategy is suitable to prevent too high hot-spot temperatures. [ABSTRACT FROM AUTHOR]

The quench protection in high-temperature superconducting (HTS) magnets is a well-known issue. Therefore, it is fundamental to have reliable models available for the analysis of the quench propagation in such magnets. The quench propagation in an ENEA HTS cable-in-conduit conductor, developed for fusion applications with the particular reference to an insert for the central solenoid of the Italian Divertor Tokamak Test (DTT) facility, is analyzed here with a new 1-D multiregional thermal-hydraulic and electric model, based on dedicated preliminary analyses and experimental and numerical characterization of the conductor. It is shown that large temperature differences arise in the conductor cross section during the quench propagation. The model is then applied to parametrically assess the effects of delay and fast current-discharge times on the conductor peak temperature, to avoid damaging the HTS. The parametric study shows that both the delay and current discharge time should stay below 0.5 s, to keep the peak temperature below 150 K. [ABSTRACT FROM AUTHOR]

The introduction of artificial pinning sites in YBa2Cu3O7-δ (YBCO) epitaxial thin films has been obtained by pulsed laser deposition (PLD) technique from YBCO-BaZrO3 (BZO) composite targets with BZO concentration ranging from 2.5 to 7 mol %. The typical critical temperature, Tc, drop observed in YBCO-secondary phase films grown by PLD has been successfully recovered by increasing the deposition temperature. Transport properties analyses revealed improved pinning force values for YBCO-BZO films for BZO concentration above 5 mol %. These films exhibited an anomalous dual peak structure which has been ascribed to the presence of two pinning contributions. The crossover field, Bm, separating these two pinning regimes has been observed to be temperature independent suggesting the occurrence of the matching field effect. The measured value of Bm agreed with the matching field value, B[uppercase_phi_synonym]=Knd[uppercase_phi_synonym]0, as evaluated from transmission electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below Bm in all the temperature range inspected. On the contrary, in the high magnetic field range (above Bm), the effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting that at low temperatures the dominant pinning contribution arises from isotropic pinning centers. [ABSTRACT FROM AUTHOR]

The presence of lattice correlated disorder in real materials places further demands on the understanding of the structure-function relationship. The study of this disorder is quite challenging, since it can be due to various and interconnected reasons. This requires advanced probes able to measure weak structural features. Thanks to synchrotron radiation features, nowadays, it is possible to visualize structural disorder alongside its spatial distribution and time dynamics. In this context, we aim to characterize thin-film superconducting YBa2Cu3O7-x, whose structure is particularly rich. Indeed, here, the nanogranularity related to superlattices, distribution of dopants, and strain-induced stoichiometry inhomogeneity are coupled with the intrinsic granularity arising fromthe material island growth mode, which leads to small grains (~200 nm) and a large network of grain boundaries. X-rayGrazing incidence diffraction has been used to visualize lowdimensional lattice disorder in optimally doped YBa2Cu3O7-x with inclusion of BaZrO3 nanodefects grown on SrTiO3 single crystals. The results are expected to shade light on interplay of lattice disorder and the electronic quantum coherence in the superconducting state. [ABSTRACT FROM AUTHOR]

The growth of oriented buffer layers by chemical solution deposition (CSD) on cube-textured Ni-based substrate is a key point for the development of low-cost YBa2Cu3O7-x (YBCO) coated conductor. Among the suitable compounds, La2Zr2O7 (LZO) and CeO2 are of particular interest as they enabled an all-chemical route for the fabrication of YBCO coated conductor. It has been recently shown that CSD films can be grown by direct precurson solution deposition on as-rolled, i.e., without cube orientation, metallic substrate. In particular, LZO film with biaxially {001}<110> texture has been successfully grown on either pure copper or Ni-W alloy substrate. In the present contribution, the deposition either LZO or Zr-doped CeO2 (CZO) on as-rolled Ni 3.5 at% W (Ni-W) substrate is reported. It is shown that film orientation enhances using low-roughness substrates, with an area fraction of {001}<110> oriented film as high as 96.4% for LZO and 95.4% for CZO. In both cases, the films are well adherent, without blister formation or delamination. Moreover, the film acts as a planarization layer, by smoothing Ni-W intrinsic roughness, also in correspondence of Ni-W grain boundary, where no grooving seems to appear on film surface. [ABSTRACT FROM AUTHOR]

The ex situ chemical solution deposition route for YBabCubO7-δ (YBCO) epitaxial nanocomposite films' growth is one of the most promising approaches for low-cost and large-scale production of coated conductors for high magnetic field applications. A key advantage of this method is that the nanoparticle (NP) dimension, concentration, and composition can be finely controlled and defined before the deposition process. However, in order to scale up the ex situ process, important and challenging problems remain to be solved, because NPs coalescence, precipitation, and reactivity can cause film-quality degradation. With the aim of overcoming these issues, the possibility of improving YBCO properties by the use of nanodiamond (ND) as artificial pinning center (APC) has been investigated. ND and, in general, carbon-based nanomaterials (CBN) are certainly among the most promising materials developed in the recent years due to their unique mechanical and electronic properties. Among the many proposed applications for CBN, their use in the field of high critical temperature superconductors has not still been fully developed, despite the undoubted advantages in terms of stability and size control of NP. In the present work, the effect of ND addition to YBCO precursor solution on structural and morphological film properties has been estimated and preliminary results have been used to understand if ND can be considered a reliable new tool for APC introduction. [ABSTRACT FROM AUTHOR]

High temperature superconducting tapes based on cuprate compounds are nowadays available on long lengths by several companies. Because high superconducting properties are strongly influenced by the crystallographic orientation of the superconducting film, and because the appropriate crystallographic orientation is obtained through epitaxial film growth, the development of an oriented template is of crucial technological importance. In the rolling assisted biaxially textured substrate (RABiTS) technique, a strong cube texture is obtained by cold rolling fcc metal tape and high temperature annealing, followed by the deposition of one or more buffer layer by either physical vapor deposition (PVD) or chemical solution deposition (CSD). Using the latter approach, it has been recently shown that it is possible to combine substrate recrystallization and buffer layer growth in a single step if the onset of recrystallization occurs at a temperature lower than buffer layer nucleation. In the present contribution, a detailed investigation of biaxially-oriented La 2 Zr 2 O 7 (LZO) buffer layer grown on cold-rolled Ni-W substrate by combined EBSD, AFM and TEM analyses is reported. It is shown that it is possible to obtain highly {001}〈110〉-textured LZO film directly on cold-rolled Ni-W substrate. Although some small polycrystalline regions appear, this approach leads to a strong suppression of grain boundary grooving typically occurring in RABiT-type substrates. Further, it is shown that, notwithstanding the microstructure of the metal substrate continues to evolve during the conversion heat treatment, the obtained LZO film is well adherent, without cracks or delamination. [ABSTRACT FROM AUTHOR]

Electrical and mechanical characterizations of YBCO coated conductors diffusion joints obtained in a 2 mm wide, Cu stabilizer free commercial tape provided by SuperPower Inc. were reported. Two conductor pieces were overlapped for a length of 20 mm and kept in contact under a pressure as high as 80 MPa. A face-to-face approach was used, with or without an additional Ag tape insert. The joint was realized by Ag diffusion at a temperature of 200 and 400°C in N2 and O2 atmosphere, respectively. The resistivity of the joint was measured at 77 K in N2 bath. The mechanical properties of the joint were characterized by means of single-lap tensile test operated at room temperature at a rate of 0.5 mm/min. The best results were obtained by high temperature joining in O2 atmosphere. The resistivity of the joints was as low as 3.1 x 10-12 Ωm². This value is almost halved if an Ag insert is used. The mechanical properties of the joints are strongly dependent on the use of an Ag insert, since maximum load as high as 60 N can be applied if no additional insert is used. This value enhances to about 100 N when an Ag insert is employed. However, the joint obtained at low temperature in N2 atmosphere is also interesting since the joint resistivity was slightly increased to 4.7 x 10-12 Ωm² and a maximum load as high as 50 N was obtained indicating that diffusion joints can be safely handled. These results are promising in perspective of oxygen free diffusion joints in Cu stabilized coated conductors. [ABSTRACT FROM AUTHOR]

A detailed study on YBa2Cu3O7-δ (YBCO) films with BaZrO3(BZO) inclusions (YBCO-BZO) deposited on SrTiO3 substrate with different BZO contents is presented. X ray diffraction, SEM imaging and superconductive critical temperature (Ta) measurements were performed to evaluate film growth quality. Independently from the BZO content, all YBCO-BZO films showed Tc values close to that of pure YBCO indicating that the Tc reduction which is usually observed on YBCO-BZO films can be successfully recovered by changing the deposition conditions. All YBCO-BZO films showed an improved critical current density (Jc) dependence on magnetic field if compared to the typical Jc(H) of YBCO, resulting in higher irreversibility fields up to 9 T at 77 K. SEM observation on etched samples suggests a direct link between the defect density measured in YBCO-BZO samples and that calculated from the observed in field performances. The analysis of Jc(B) as a function of applied magnetic field direction revealed that the pinning due to isotropic pinning centers typical for YBCO is coupled with a c-axis correlated pinning in YBCO-BZO which can be ascribed to BZO induced columnar defects. Jc(B) recorded at several temperatures down to 10 K revealed matching effect features. [ABSTRACT FROM AUTHOR]

The working features of 2nd generation high temperature superconducting tapes related to applications, such as their stability, are becoming of real interest as long tape lengths become available. In this work, we present results on normal zone propagation velocity obtained on a 40 cm long YBCO coated conductor, called 344 superconductors, manufactured by American Superconductor Corp. Although the tape is wound on a 40 mm diameter cylinder support, its transport features are unaffected compared to the straight tape. The quench is induced by an external heater, and the propagation is observed from the increasing voltages along the tape. In the range 75 ÷ 80 K, we observed a propagation velocity lower than 2 cm/s at current bias slightly below 80% of the critical current. Our investigation covers different bias current values as well as temperatures, and experimental analysis is also compared to an approximate numerical model. [ABSTRACT FROM AUTHOR]

The addition of artificially induced defects improves the pinning efficiency of magnetic flux vortices in YBa2Cu3O7-δ (YBCO) films. In YBCO films by pulsed laser ablation (PLD) technique this goal can be pursued by the introduction of epitaxial second phase nanoinclusions in the YBCO matrix. In the present work, the effect of BaZrO3 (BZO) inclusions in stoichiometric YBCO films on transport properties has been studied. Composite targets obtained by addition of BZO powder in molar percents ranging from 2.5 to 7 mol. % have been prepared with BZO mean grain size of about 1 μm. Structural and morphological characterizations of the films obtained by PLD from these targets have been carried out through X-ray diffractometry and Scanning Electron Microscopy (SEM) analysis. Dc electrical transport measurements at 77 K have revealed a better magnetic field retention of the critical current density, Jc, being at 3 T the 14.6% and the 16.4% of the zero field values for YBCO-BZO 5% and 7%, respectively. The complex surface impedance has been measured by means of a dielectric resonator at a high microwave frequency (50 GHz). In order to identify the potentially strong pinning induced by the inclusions, the field-dependent complex resistivity has been determined as a function of temperature in a moderate magnetic field (B < 1 T). Very high depinning frequency are estimated in YBCO films with BZO inclusions indicating extremely high vortex pinning and steep potential wells. [ABSTRACT FROM AUTHOR]

The realization of high critical current density YBCO-based coated conductors in the RABiTS approach is primarily related to the sharpness of cube texture developed in the substrate. Among the various proposed Ni-based tapes, Ni-W alloys have attracted a particular interest either because of the enhanced mechanical properties and reduced magnetism with respect to pure Ni, or of the sharp and almost pure cube texture that can be induced. The only other remarkable component associated with cube orientation consists of its twins, whose formation is known to be primarily determined by the stacking fault energy, which is a characteristic of the material. Despite this fact, the obtained textures for a given material can significantly vary, suggesting that the deformation regime, as well as the initial bulk conditions, have a role in influencing twins formation. In this contribution, the effect of the strain conditions during mechanical deformation and initial bulk grain size on the final recrystallization texture are evaluated. EBSD and x-ray analyses evidence the influence of the initial grain size on the recrystallization texture, since sharper cube textures with reduced non-cube components develop in finer-grained starting material. Conversely the condition of plane strain deformation plays no role in determining the recrystallization texture. [ABSTRACT FROM AUTHOR]

Abstract: The improvement of the critical current density in YBCO coated conductor tapes necessarily concerns the study of grain boundary (GB) properties and the study of different pinning mechanisms involving both GB and the interior of the grain (IG). Recently, it has been proposed that the introduction of Ca substituting Y enhances J c in YBCO grain boundaries (GB). On the other hand enhanced correlated pinning, as observed in YBCO thin films grown on CeO2 buffered substrates, has been ascribed to elongated defects along the c-axis of the film. In order to evaluate the role of calcium and CeO2 buffer layer on the superconducting transport properties of YBCO films, critical current density measurements as a function of temperature, magnetic field and angle between magnetic field direction and c-axis of the film have been performed on epitaxial thin films of unsubstituted and 10at.% Ca substituted YBCO grown on CeO2 buffered Al2O3 single crystal substrates. Results are compared with data obtained on 10at.% Ca substituted YBCO grown on SrTiO3 single crystal substrate. [Copyright &y& Elsevier]

We report on the superconducting properties of epitaxial thin films Y1-xCaxBa2Cu3O7-y with 0 £ x ³ 0.2, grown on SrTiO3 (001) by Pulsed Laser Deposition (PLD) technique. The partial substitution of Ca2+ at the Y3+ site in YSCO leads to a monotonic decrease of the zero resistance critical temperature, Tc. The oxygen stoichiometry is varied by means of post-deposition thermal treatment varying the oxygen partial pressure. The dependence of Tc on annealing oxygen pressure can be attributed to an overdoping effect and/or to a cation disorder. [ABSTRACT FROM AUTHOR]

We investigate the effect of partial substitution of Y by Ca in YBCO superconducting thin films. The films were grown on (1 0 0) SrTiO3 single crystal substrates by pulsed laser deposition (PLD). The Ca doped film were ablated from Y1−xCaxBa2Cu3O7−δ targets with x=0, 0.05, 0.07, and 0.10. The dc transport properties of the films in applied magnetic field are analyzed to study the role of Ca on the superconducting properties of YBCO films. The irreversibility line for the samples with x=0 and 5 at.% Ca was derived from the E–J curves using a scaling theory for the vortex-glass transition. [Copyright &y& Elsevier]

The fabrication of a Fe-based coated conductor (CC) becomes possible when Fe(Se,Te) is grown as an epitaxial film on a metallic oriented substrate. Thanks to the material's low structural anisotropy, less strict requirements on the template microstructure allow for the design of a simplified CC architecture with respect to the REBCO multi-layered layout. This design, though, still requires a buffer layer to promote the oriented growth of the superconducting film and avoid diffusion from the metallic template. In this work, Fe(Se,Te) films are grown on chemically-deposited, CeO2-based buffer layers via pulsed laser deposition, and excellent properties are obtained when a Fe(Se,Te) seed layer is used. Among all the employed characterization techniques, transmission electron microscopy proved essential to determine the actual effect of the seed layer on the final film properties. Also, systematic investigation of the full current transport properties J(θ, H, T) is carried out: Fe(Se,Te) samples are obtained with sharp superconducting transitions around 16 K and critical current densities exceeding 1 MA cm−2 at 4.2 K in self-field. The in-field and angular behavior of the sample are in line with data from the literature. These results are the demonstration of the feasibility of a Fe-based CC, with all the relative advantages concerning process simplification and cost reduction. [ABSTRACT FROM AUTHOR]

In this paper we study the feasibility of Fe(Se, Te) coated conductors on a simple rolling-assisted biaxially textured substrate (RABiTS) template. Starting from commercially available Ni–5 at% W tapes which show an out-of-plane orientation of about 7° and an in-plane orientation around 5°, we realized a RABiTS template for Fe(Se, Te) coated conductor fabrication by depositing CeO2 thin films on the metallic tape. The oxide buffer layers, deposited via pulsed laser ablation, exhibit an out-of-plane and an in-plane orientation suitable for Fe(Se, Te) deposition and act as a chemical barrier against Ni diffusion. Fe(Se, Te) thin films deposited on such a simple template show a superconducting transition at 16 K and very high upper critical field values with a ΔTc,0 of only 3 K in 18 T. The transport critical current reaches values of 1.7 × 105 A cm−2 at 4.2 K in self-field and is reduced by less than one order of magnitude up to 18 T, remaining isotropic with respect to the magnetic field direction. [ABSTRACT FROM AUTHOR]

The 1144 family of Iron Based Superconductors (IBSCs) is characterized by critical currents among the highest for single crystalline IBSCs. The synthesis of polycrystalline compounds is usually carried out through high temperature (T > 900 °C) processes. These methods, justified by a supposed thermodynamic instability of the 1144 phase at low temperature, are complicated by the presence of highly volatile elements and require fast heating and cooling steps. Here, it is shown how a High Energy Ball Milling (HEBM) treatment is effective to promote the reaction among the starting elements, thus favoring the synthesis of the 1144 phase at lower temperature. The evolution of the powders has been assessed for different milling times, observing the consumption of the starting reactants and the formation of crystalline pnictide phases. Different thermal treatments have been coupled to the HEBM treatment, allowing the study of the effect of time and temperature of the thermal step on the materials properties. It has been observed how the formation of the superconducting phase occurs on the HEBM samples at 500 °C and 600 °C. Critical temperatures comparable with data reported in the literature were obtained. Granularity phenomena and critical current density of sintered samples are highly dependent on the processing variables. [ABSTRACT FROM AUTHOR]

Cable-in-conduit conductors comprised of twisted stacks of high-temperature superconducting (HTS) tapes constitute a very promising technology by virtue of their easy manufacturing process, flexibility capabilities, and high current densities. In a cable, the current distribution among tapes is one of the key parameters affecting the cable performances. The distribution of current is affected mainly by the self-field configuration (ultimately related to the cable layout) and the termination resistances. In this paper we present a 2D finite element (FE) model, based on the T-A formulation, which computes the magnetic field and current distribution in stacked tapes. This model has been used to describe the experimental V–I results obtained in cables in which different current distributions among tapes are expected. The first case refers to V–I curves of stacks of HTS tapes inserted into ducts formed in the extruded aluminium cylindrical core for a straight cable. The excellent agreement between the experimental findings and the simulation results can be explained in terms of uniform current distribution within the tapes stack, up to the superconducting to normal transition. The second sample, an Al-slotted core Cable-In-Conduit-Conductor, has been bent down to a radius of 0.15 m, and from the measured V–I characteristic of each individual tape, a different tape degradation depending on the tape position within the stack was recorded. The model is able to reconstruct the V–I of the stacks from the characteristic curves of the individual tapes with a satisfactory agreement. The finite element analysis reveals non-uniform current distribution among the tapes, which could expose the cable to a potentially irreversible damage during operation. The proposed FE model constitutes a useful tool for the analysis and predictions of HTS CIC conductor performances and represents a suitable basis for the implementation of more complex models aimed at the design of specific and large applications of this conductor in the next future. [ABSTRACT FROM AUTHOR]

In order to study the vortex pinning determined by artificially introduced pinning centers in the small-vortex displacement regime, we measured the microwave surface impedance at 47.7 GHz in the mixed state of YBa2Cu3O7-δ thin films, where submicrometric BaZrO3 particles have been incorporated. As a function of the BaZrO3 content, we observed that the absolute losses slightly decrease up to a BaZrO3 content of 5%, and then increase. We found that the magnetic-field-induced losses behave differently in that they are not monotonic with increasing BaZrO3 concentration. At small concentration (2.5%) the field-induced losses increase, but large reduction in the losses themselves, by factors up to 3, is observed upon further increasing the BaZrO3 concentration in the target up to 7%. Using measurements of both surface resistance and surface reactance, we estimate vortex pinning-related parameters. We found that BaZrO3 inclusions introduce deep and steep pinning wells. In particular, the minimum height of the energy barrier for single vortices is raised. At larger BaZrO3 content (5% and 7%) the phenomenon is at its maximum, but it is unclear whether it shows a saturation or not, leaving room for further improvements. [ABSTRACT FROM AUTHOR]

• Inductive measurements on Nb3Sn rectangular WR1 European DEMO conductor and strands. • Determination of critical temperature distribution in the cable cross-section. • Determination of thermal strain distribution in the cable cross-section. • Reading of DC performances by means of strain distribution in the cross-section. The knowledge of the strain distribution of Nb 3 Sn filaments in a CICC cross-section is a key parameter in understanding the performance and its evolution when the cable undergoes electromagnetic cyclic loading. This work focuses on the Wind and React (WR1) rectangular CICC sample designed by ENEA for the European DEMO project, that has exhibited a current sharing temperature (T cs) above 6.9 K at 13 T and 81.7 kA, during its qualification tests in the EDIPO facility at the Swiss Plasma Center. Compared to the critical current tests on the constituting wires, the observed CICC performance corresponded to an effective strain value of −0.55%. This work aims to interpret this result on the basis of the analysis of the strain distribution inside the cable itself. Susceptibility versus temperature of WR1 constituting free standing strands has been measured after etching of the stabilizing copper, and it has been compared with the susceptibility measured on the cable during the test campaign in EDIPO. A well-known and already assessed method has been used, starting from susceptibility measurements, to compute the T c distribution in the cable cross-section and, subsequently, to infer from that the thermal strain distribution. The obtained results give an indication that the strain distribution in WR1 cable is narrow, compared to the strain distribution calculated with the same method for most ITER TF and CS conductors. [ABSTRACT FROM AUTHOR]

Abstract: In this work transport properties of superconducting 10at.% Ca-substituted YBCO thin films grown on (100)-SrTiO3 single crystal substrate (STO) and superconducting pure and 10at.% Ca-substituted YBCO thin films grown on CeO2 buffered Al2O3 substrates (CAO) have been analyzed as a function of the temperature, applied magnetic field and angle between magnetic field direction and the direction normal to the film surfaces. Particularly, the angular analysis provides an easy way to discriminate between isotropic point defects and correlated pinning sites. Despite the intragrain pinning mechanisms remained unaffected by Ca substitution, a detrimental effect on grain boundary properties clearly emerged for 10at.% Ca concentration. This effect is enhanced in sample grown on CeO2 buffered sapphire where a more disturbed grain boundary is expected resulting in an enhancement of the correlated pinning, already observed in pure YBCO films grown on CAO, and in a reduction of the intrinsic pinning efficiency. [Copyright &y& Elsevier]

In the effort to unveil the relations between synthesis conditions, morpho-structural features and superconducting properties of (11)-type iron-based superconductors, this study is focused on FeSe0.5 Te0.5 materials obtained from high-temperature melts and different cooling rates. Crystalline and chemical composition are evaluated by means of XRD and SEManalyses, highlighting the formation of complex multiphase structures: the obtained results suggest that high-temperature nucleating phases may play a key role in the observed phase separation. Superconducting properties, evaluated by magnetization measurement and dc electrical resistance in different magnetic field conditions up to 18 T, highlight the low homogeneity of the superconducting phases, reflecting the microstructural observation. [ABSTRACT FROM AUTHOR]

Measurements of anisotropic transport properties (dc and high-frequency regime) of driven vortex matter in YBa2Cu3O7-x with elongated strong-pinning sites (c-axis aligned, self-assembled BaZrO3 nanorods) are used to demonstrate that the effective-mass angular scaling takes place only in intrinsic physical quantities (flux-flow resistivity), and not in pinning-related Labusch parameter and critical currents. Comparison of the dynamics at different time scales shows evidence for a transition of the vortex matter toward a Mott phase, driven by the presence of nanorods. The strong pinning in dc arises partially from a dynamic effect. [ABSTRACT FROM AUTHOR]

Abstract: YBa2Cu3O7− δ thin films with BaZrO3 (BZO) inclusions have been deposited on SrTiO3 substrates in order to study the effect of nanoparticles addition into YBCO matrix. Samples with 7% (mol) BZO content were obtained by PLD varying the deposition conditions, in order to evaluate their effect on the films transport properties. The change in deposition parameters, especially of the deposition temperature, has been discovered to be efficient for a reduction or complete recovery of the critical temperature decrease produced by BZO addition. The effect of the deposition temperature on in-field films transport properties as well as on the presence of c-axis correlated defects typically ascribable to nanoparticles addition, can be recognised in an improvement in JC retention in applied magnetic field and, for higher temperatures, the appearance of correlated pinning contribution, as confirmed by pinning force density measurements. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed investigation of the self-field transport properties of an ionic liquid gated ultra-thin YBa2Cu3O7-x (YBCO) film. From the high temperature dynamic of the resistivity (>220 K), different scenarios pertaining to the interaction between the liquid and the thin film are proposed. From the low temperature evolution of Jc and Tc, a comparison between the behavior of our system and the standard properties of YBCO is drawn. [ABSTRACT FROM AUTHOR]

We present a study of the anisotropic vortex parameters as obtained from measurements of the microwave complex resistivity in the vortex state with a tilted applied magnetic field in YBa2Cu3O7-x thin films with BaZrO3 nanorods. We present the angular dependence of the vortex viscosity η, the pinning constant kp and the upper limit for the creep factor χM. We show that the directional effect of the nanorods is absent in η, which is dictated by the mass anisotropy γ. By contrast, pinning-mediated properties are strongly affected by the nanorods. It is significant that the pinning and creep affected by the nanorods is detectable also at our very high operating frequency, which implies very short-range displacements of the vortices from their equilibrium position. [ABSTRACT FROM AUTHOR]

Chemical solution deposition (CSD) is a versatile and cheap technique widely used for both buffer layer and YBa2Cu3O7−δ (YBCO) epitaxial film growth. One of the main limits hindering the widespread use of the CSD technique in the field of coated conductors is the limited film thickness that can be reached without degradation. Among the different strategies adopted to obtain thicker film by CSD, increase of precursor solution concentration and viscosity can be mentioned. Another interesting approach is the use of multilayer deposition in order to overcome the limits of CSD technique. Multilayer deposition has been so far realized by performing a complete heat treatment - or at least a pyrolysis step - after each deposited layer, resulting in increased processing time and overall cost. In this contribution, we show that an epitaxial multilayer buffer can be easily obtained by means of multiple successive depositions, in which after each layer only a fast drying step of the precursor solution is carried out. In this way, only a single conversion heat treatment can be used. This approach not only allows a significant reduction on the processing time but also it is more suitable for the growth on metallic template. The viability of this approach is shown by using multilayer Zr-doped CeO2 buffer deposition on single crystalline YSZ substrate. It is shown that, up to 8 layers, no significant structural and morphological degradation of the buffer layer occurs. Further, YBCO film grown by CSD was used to test the suitability of multilayer buffer. YBCO film grown on multilayer buffer shows excellent superconducting properties, with zero-resistance critical temperature up to 92 K and a critical current density exceeding 1 MA/cm2 at 77 K in self field. [ABSTRACT FROM AUTHOR]

Among other Fe-based superconductors, Fe(Se,Te) is particularly interesting because of the low structural anisotropy, large upper critical fields, low field dependence of the critical current density and low toxicity. It can also be grown as an epitaxial film on a metallic oriented substrate, making the fabrication of a Fe-based coated conductor (CC) possible. Less strict requirements on the template microstructure allow for the design of a simplified design compared to REBCO CCs. This design requires a buffer layer to promote the oriented growth of the superconducting film and avoid diffusion from the metallic template. In this work, CeO2 based buffer layers are prepared on single crystals via two chemical deposition techniques, metal organic decomposition (MOD) and polymer assisted deposition (PAD). With the design of a suitable thermal treatment, it is possible to obtain oriented buffers with large flat grains and low values of surface roughness. Fe(Se,Te) films are deposited on these templates via laser deposition, and excellent samples are obtained when a Fe(Se,Te) seed layer is used to favour chemical matching with the buffer: sharp superconducting transitions around 16 K and critical current densities exceeding 1 MA cm−2 at 4.2 K in self-field are observed. These results are the demonstration of the feasibility of a Fe-based CC architecture, with all the relative advantages concerning process simplification and cost reduction. [ABSTRACT FROM AUTHOR]

We investigate the effect of the anisotropy and of the directional pinning in YBaCuO films grown by pulsed laser ablation from targets containing BaZrO at 5 mol%. BaZrO inclusions self-assemble to give nanorods oriented along the c-axis, thus giving a preferential direction for vortex pinning. The directionality of vortex response is studied at high ac frequency with the complex microwave response at 48 GHz, as a function of the applied field and of the angle θ between the field and the c-axis. The complex microwave response does not exhibit any angular scaling, suggesting that the structural anisotropy of YBaCuO is supplemented by at least another preferred orientation. The pinning parameter r shows evidence of directional pinning, effective in a wide range of angles around the c-axis (thus ascribed to BZO nanocolumns). [ABSTRACT FROM AUTHOR]

In multi-filamentary superconducting strands the transverse resistivity gives a fundamental contribution to the mechanisms governing the coupling losses in AC regime and the current transfer length, for example influencing the performance of Nb3Sn wires with bending strain. Nevertheless, the transverse resistance matrix generally used into the simulation codes of superconducting strands is determined as a fitting parameter obtained from the experimental V-I curves. The first direct measurement of the transverse resistance as a function of the temperature in Nb3Sn multi-filamentary wires by using a 4-probe method has been performed at ENEA. Here we study the effect of a background magnetic field on the V-I characteristics, obtaining interesting results. Moreover, the resistivity between the Nb3Sn bundles and the outer copper layer is measured at different temperatures. These experimental values, together with the inter-bundle resistivity, are inserted as input parameters in the strand current diffusion equations, for the validation of a finite differences numerical model. The agreement between simulated V-I curves and experimental characteristics is excellent. [ABSTRACT FROM AUTHOR]

Ca/K-1144 compounds have been described widely in literature as stoichiometric compounds, with a Ca:K ratio equal to unity. In this work, we demonstrate that Sr ions can substitute K ions in the 1144 lattice. Polycrystalline samples were produced via a mechanochemically assisted synthesis route. Sr substitution in the Ca/K compound leads to a shortening of its c axis, while no differences are appreciable from the morphological point of view. The CaK0.9Sr0.1Fe4As4 compound is characterized by a slightly reduced critical temperature of approximately 31 K, with respect to the 35 K of the pristine compound. The role of lattice distortion carrier concentration or structural disorder that may be accounted for the reduction of critical temperature is here discussed. [ABSTRACT FROM AUTHOR]

The structural and transport properties of YBa2Cu3O7−x films grown by pulsed laser deposition with mixed 2.5 mol% Ba2YTaO6 (BYTO) and 2.5 mol% Ba2YNbO6 (BYNO) double-perovskite secondary phases are investigated in an extended film growth rate, R = 0.02–1.8 nm s−1. The effect of R on the film microstructure analyzed by TEM techniques shows an evolution from sparse and straight to denser, thinner and splayed continuous columns, with mixed BYNO + BYTO (BYNTO) composition, as R increases from 0.02 nm s−1 to 1.2 nm s−1. This microstructure results in very efficient flux pinning at 77 K, leading to a remarkable improvement in the critical current density (Jc) behaviour, with the maximum pinning force density Fp(Max) = 13.5 GN m−3 and the irreversibility field in excess of 11 T. In this range, the magnetic field values at which the Fp is maximized varies from 1 T to 5 T, being related to the BYNTO columnar density. The film deposited when R = 0.3 nm s−1 exhibits the best performances over the whole temperature and magnetic field ranges, achieving Fp(Max) = 900 GN m−3 at 10 K and 12 T. At higher rates, R > 1.2 nm s−1, BYNTO columns show a meandering nature and are prone to form short nanorods. In addition, in the YBCO film matrix a more disordered structure with a high density of short stacking faults is observed. From the analysis of the Fp(H, T) curves it emerges that in films deposited at the high R limit, the vortex pinning is no longer dominated by BYNTO columnar defects, but by a new mechanism showing the typical temperature scaling law. Even though this microstructure produces a limited improvement at 77 K, it exhibits a strong Jc improvement at lower temperature with Fp = 700 GN m−3 at 10 K, 12 T and 900 GN m−3 at 4.2 K, 18 T. [ABSTRACT FROM AUTHOR]

YBa2Cu3O7–x (YBCO) films grown by metal-organic decomposition (MOD) are promising candidates for the production of high performance high temperature superconductors (HTS) tapes. Moreover, artificial pinning centers (APCs) introduction proved to be a powerful tool for the improvement of transport properties in YBCO films. Along with the widely employed pinning strategies, such as the introduction of secondary phases in the YBCO matrix, a less studied approach is the nanostructuring of the YBCO substrate, in order to hinder its growth and to obtain a highly defective superconductive layer. In this work, oxide nanostructures were deposited on crystalline substrates via polymer assisted deposition (PAD), a low cost, highly versatile technique, so as to create nanoparticles that could interfere with epitaxial growth of chemical YBCO films. Preliminary analyses of the superconducting films grown on BaZrO3 (BZO) and ZrO2 (ZO) nanostructures showed that the decorated templates are highly effective in straining the YBCO matrix, leading to a significant improvement in transport properties. In fact, we obtain an increase of the critical current density, at 77 K, for YBCO grown on BZO and ZO decorated substrate of the order of 3 times at 2 T and even of the order of 8 times at 5 T with respect to the YBCO grown on bare substrate. The improvement of the pinning properties can be related to the intrinsic modification of the crystal structure of YBCO film due to the presence of these nanoparticles, in agreement with transmission electron microscopy (TEM) analysis performed. [ABSTRACT FROM AUTHOR]

Superconducting properties of the Fe(Se,Te) system are directly related to its microstructure. However, in the framework of a not well assessed phase diagram, a large spread of chemico-physical and functional properties is reported for compounds characterized by similar overall chemical compositions. This is in particular observed in materials produced by melting routes, where chemical inhomogeneities and multiple phases are commonly obtained. Both composition and morphology of these inhomogeneities seem to play a role in the behaviour of the superconducting phases, pointing out the need to assess the dependence of phase composition and therefore of the material performance on the sample thermal history. In this work, the effect of different post-synthesis annealing treatments is studied. A melting route has been adopted to synthesize polycrystalline samples, subsequently subjected to thermal treatments at different temperatures. Morphology and microstructure were characterized by means of x-ray diffraction and microscopy techniques. The superconducting properties have been evaluated by means of electrical and magnetic measurements. It is observed how microstructure, chemical composition and morphology of the obtained products strictly depend on the annealing temperature. Moreover, a crucial role of the cooling step is evidenced: in fact, a rapid cooling procedure from high temperature leads to the formation of high temperature (Tconset > 19 K) superconducting phases, but the overall bulk superconducting performance is negatively affected. Other annealing treatments can promote instead an enhancement in the critical current at high fields with respect to pristine sample, suggesting that a careful engineering of a post-synthesis thermal step can represent a useful tool to optimize the material properties. [ABSTRACT FROM AUTHOR]

The epitaxial growth of Zr-doped CeO2 (CZO) films by chemical solution deposition (CSD) on single crystal substrates such as Al2O3, SrTiO3 and Y2O3-stabilized ZrO2 (YSZ) and their use as buffer layers for Fe(Se,Te) film growth are reported. The growth of 30 nm thin CZO films is mostly dominated by dewetting issues, leading to highly incomplete substrate coverage due to the strong tendency of CZO grains to agglomerate. This effect is less severe on YSZ substrate and, in addition, can be fully controlled by setting the deposition temperature at 950 °C and operating under Ar–H2 reducing atmosphere. These conditions promote the growth of epitaxial and compact CZO films on YSZ, showing a flat surface morphology with root-mean-square roughness around 2.5 nm. Preliminary results on Fe(Se,Te) film deposited by pulsed laser deposition on CZO-buffered YSZ are reported. Although good epitaxial growth is achieved on CZO buffer layer, Fe(Se,Te) films exhibit poor superconducting properties. On the other hand, Fe(Se,Te) films show excellent properties when a seed layer is used, exhibiting a sharp superconducting transition at about 17 K and a critical current density exceeding 1 MA cm−2 at 4.2 K in self field. The main role of the seed layer, consisting of a non-superconducting Fe(Se,Te) film, is to favour the crystal and chemical matching between buffer layer and film, allowing for the growth of high-quality superconducting Fe(Se,Te) at deposition temperature as low as 200 °C. In perspective of applications, this result is a significant step towards process simplification and cost reduction of Fe(Se,Te)-based coated conductor technology development, being the first demonstration of superconducting Fe(Se,Te) films grown on CSD buffer layer. [ABSTRACT FROM AUTHOR]

In this study, chemically decorated surfaces are employed as tools for Artificial Pinning Centres (APC) introduction in superconducting YBa 2 Cu 3 O 7−x (YBCO) films. Self-assembled oxide nanostructures are grown on crystalline substrates via a very versatile and low-cost chemical technique called Polymer Assisted Deposition (PAD). Such decorated templates are used, in a second step, as substrates for YBCO film growth via Metal Organic Decomposition (MOD) or Pulsed Laser Deposition (PLD). The aim of the structures is to produce in the superconducting matrix strain and/or defects that should act as APCs and therefore enhance the transport properties of the samples. The oxides selected for the decoration are commonly used for the introduction of artificial pinning centres in YBCO: BaZrO 3 and ZrO 2. The decorated surfaces are analyzed via Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). YBCO films have been characterized via SEM, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), DC resistivity and critical current measurements. The results show that the nanostructures are stable and that they can efficiently introduce strain and stacking faults in the film. This causes an increase in the value of the critical current density J c and better in-field behaviour in all the investigated field range, compared to the analogous film grown on a standard substrate, especially for chemically derived YBCO. Also J c angular dependence measurements, J c (θ), show an isotropic enhancement of the critical current for every angle of application of the field. Unlabelled Image • Surface decoration with BaZrO 3 and ZrO 2 nanoislands has been carried out via Polymer-Assisted-Deposition on single crystals • Microstructural analyses show that the nanostructured substrates can introduce strain and defects in YBa 2 Cu 3 O 7 -x films • Direct transport measurements reveal J c enhancement and better in-field behaviour for the samples grown on the nanoislands [ABSTRACT FROM AUTHOR]

Abstract Superconducting YBa 2 Cu 3 O 7-δ films with different amounts of BaZrO 3 nanoinclusions were deposited on SrTiO 3 (001) by low-fluorine chemical solution deposition with the aim of introducing artificial vortex pinning centres. The Zr concentration over the film thickness could be determined by X-ray photoelectron spectroscopy combined with Ar+ ion etching. The Zr/Y ratio has a constant behaviour in the film's bulk. Zr segregation occurs near the surface and Zr diffusion into the substrate is observed near the interface. Conversely, Sr and Ti from the substrate diffuse into the films. Y3d lineshape analysis and X-Ray Diffraction data pointed out that Ti diffusion causes the formation of Y-Ti-O based spurious phases. Highlights • YBCO films with Zr nanoinclusions are synthesized by Chemical Solution Deposition. • The XPS Zr/Y ratio is shown to be a reliable value to determine Zr stoichiometry. • Data show the presence of a Y-Ti-O phase. • XPS depth profile analysis shows interdiffusion between substrate and film. [ABSTRACT FROM AUTHOR]

The transport and vortex pinning properties of nanocomposite YBa2Cu3O7-x (YBCO) film grown by pulsed laser deposition with addition of Ba2 Y(Nb/Ta)O6 (BYNTO) were compared with BaZrO3 added YBCO by DC (long-range vortex motion) and microwave (small-displacement vortex motion) measurement techniques. A high efficiency of BYNTO was observed in the field dependence and in the angular dependence of the critical current density Jc at 77 K, as well as in the field dependence of the complex surface impedance ΔZ. Based on the field dependence of the pinning parameters, such as the pinning parameter r and the pinning constant kp, the vortex pinning regimes were discussed. [ABSTRACT FROM AUTHOR]

Surface faceting is a well-known phenomenon occurring in either metallic or oxide materials. It is due to thermal etching favoured by high-temperature annealing in vacuum, and leads to the formation of steps or facets on the surface. The occurrence of surface faceting on cube-textured metallic substrates for YBCO coated conductor has been only seldom reported and its influence on the epitaxial growth of both buffer and superconducting layers has never been considered. In this paper, we studied the effect of the annealing conditions on the surface morphology of Ni- and Ni-Cu-based cube-textured metallic substrates and the influence of the obtained surface morphology on epitaxial film grown by both physical vapour and chemical solution deposition techniques. We confirm that annealing in reducing atmosphere suppresses both surface faceting and grain boundary grooving. Such a surface is beneficial for epitaxial film growth as it leads to smoother and featureless surfaces. On the other hand, from a microstructural point of view, film deposition on a faceted substrate shows a sharper orientation. [ABSTRACT FROM AUTHOR]

This study investigates chemically decorated surfaces as tools for the improvement of transport properties in superconducting YBa2Cu3O7-x films. This approach, still to be thoroughly investigated, makes use of low-cost easily tunable chemical methods to obtain self-assembled oxide nanostructures on a substrate that will serve, in a second step, for the deposition of the superconducting film itself. The structures are supposed to produce in the superconducting matrix a specific amount of strain, which is generally held responsible for the increased transport capacity of variously doped samples. For the growth of the nanostructures, two different methods have been employed: polymer-assisted deposition and metal-organic decomposition (MOD). The main advantages and disadvantages of these two routes are discussed. The oxide chosen for the deposition is one commonly used for artificial pinning in YBa2Cu3O7-x, namely Ba2YNbO6, together with the less common but highly interesting ferromagnetic compound La0,77Sr0,33MnO3. We also show how the density of these nanostructures can be easily controlled, and the necessary requirements for the growth of nanostructures are determined. A variety of crystalline substrates were tested for the deposition of the nanoparticles, such as SrTiO3, YSZ, MgO. YBa2Cu3O7-x films have been deposited on selected samples via standard low-fluorine MOD and characterized scanning electron microscopy (SEM), x-ray diffraction (XRD), vibrating sample magnetometer (VSM), direct current (DC) resistivity, and critical current measurements. The presence of the nanostructures results, in this case, in a slight increased value of Jc, which can be ascribed to the relatively low density of nanoparticles. [ABSTRACT FROM AUTHOR]

In this paper, a study of both pure and 5% BaZrO3 - doped YBCO low-fluorine coating solutions performed by 1HNuclear Magnetic Resonance (NMR) spectroscopic techniques is presented. This investigation enabled us to unequivocally identify the chemical species involved in the solution aging process. It was found that the presence of traces of methanol, typically used for the preparation of the solutions, promoted methyl propionate formation. Since the methanol concentration reduction in time is not completely balanced by methyl propionate formation, it is supposed that additional esterification reactions involving other acids might occur. The presence of methyl propionate ester was not recognized in solutions obtained through a refining process in which residual methanol traces were fully removed. The modification in time of the solution composition was found to be in strong correlation with the degradation of the film properties for standard solution, whereas no degradation, in the same time frame, was observed for the films prepared with the refined solutions. Indeed, both YBCO and YBCO + 5% BaZrO3 films, grown with aged refined solutions, exhibit critical temperature values above 91 K and microstructure comparable with the ones recorded in samples obtained with freshly prepared solutions. Even though the exact role of the ester in the YBCO phase formation and film quality could not be identified yet, some possible mechanisms have been proposed and discussed. [ABSTRACT FROM AUTHOR]

In the present paper, we analyze the role of in situ grown BaZrO (BZO) inclusions in YBaCuO (YBCO) thin films prepared by chemical solution deposition using a low fluorine coating solution, on the field angle dependence of the critical current density, J( 휃), data using the vortex path model. In order to form a coherent picture on the BZO doping influence on the pinning properties of the YBCO matrix, detailed structural analyses performed by X-ray diffraction techniques and microstructural evaluation by transmission electron microscopy are also presented. The evaluation of different contributions to the overall, J, permitted us to prove the effectiveness of the BZO inclusions acting as isotropic pinning centers, reflected in a uniform component of high relative value with respect to other components. For the studied 10 mol % BZO doping concentration, a threefold increase in the critical current density, J, of the YBCO host is measured, in self-field at 77 K, corresponding to a value of J=2.9MA/cm, whereas a factor 10 is measured at 1 T ( J=0.35 MA/cm). [ABSTRACT FROM AUTHOR]

Abstract: We present a microwave study of the angular dependence of the flux-flow resistivity ρ ff and of the pinning constant k p in YBCO thin films containing BZO nanorods. We find that BZO nanorods are very efficient pinning centers, even in tilted fields. We find that ρ ff is a scaling function of a reduced field H/f(θ). We extend a model for the anisotropic motion of vortices in uniaxially anisotropic superconductor, able to describe the experimental f(θ) on the basis of only the intrinsic anisotropy of YBCO. The pinning constant k p , by contrast, exhibits different field dependences in different angular ranges, consistent with pinning by BZO at angles as large as 60°, and with pinning along the a,b planes as originating from the same mechanism as in pure YBCO with the field along the c axis. [Copyright &y& Elsevier]

Abstract: We report on microwave measurements on DyBa2Cu3O7−δ monodomains grown by the top-seeded melt-textured technique. We measured the field increase of the surface resistance R s(H) in the a–b plane at 48.3GHz. Measurements were performed at fixed temperatures in the range 70K–T c with a static magnetic field μ 0 H <0.8T parallel to the c-axis. Low field steep increase of the dissipation, typical signature of the presence of weak links, is absent, thus indicating the single-domain behavior of the sample under study. The magnetic field dependence of R s(H) is ascribed to the dissipation caused by vortex motion. The analysis of X s(H) points to a free-flow regime, thus allowing to obtain the vortex viscosity as a function of temperature. We compare the results with those obtained on RE-BCO systems. In particular, we consider strongly pinned films of YBa2Cu3O7−δ with nanometric BaZrO3 inclusions. [Copyright &y& Elsevier]

MgO films are widely used as the first buffer layer in IBAD-YBCO coated conductors, whereas there are only a few examples of its use in RABiTS YBCO coated conductors. Nevertheless MgO, though challenging in terms of lattice parameter and epitaxy, can effectively passivate the metal substrate thus enabling the use of Ni–Cu-based alloy tapes. Such substrates develop a very sharp cube texture and at the same time can be safely handled when their thickness is as low as 40 \mum. Epitaxial MgO films were deposited by e-beam evaporation at 400 ^\circC on biaxially textured metal substrates. A transient Pd layer as thin as 10 nm was used to alleviate the lattice mismatch between MgO and the substrate and to enhance film adhesion. Due to the reduced diffusion of oxygen in MgO, this template is effective against substrate oxidation even in the extreme conditions typical of the YBCO growth. On such a template, La0.66Sr0.33MnO3 (LSMO) was epitaxially deposited by PLD. Moreover, BaZrO3 (BZO) film was successfully deposited by CSD on MgO single crystal and is expected to epitaxially grow also on MgO film. [ABSTRACT FROM AUTHOR]

We performed an extensive characterization of Co-doped polycrystalline 122 iron pnictide samples, Ba(Fe1-xCox)2{\ {As}}2 with x=0.07, 0.09, 0.1, 0.12, by means of high-field dc magnetization and ac 1st and 3rd harmonic susceptibility response measurements. From M(H) loops through the Bean model formula both the magnetic field and T dependences of the Jc are derived. From the 3rd harmonic response of the ac susceptibility as a function of the dc magnetic field up to 10 T recorded at different temperatures, we determined the irreversibility line, using the onset criterion. From these analyses, 7% and 9% of Co-doped samples showed the best Jc performances. [ABSTRACT FROM AUTHOR]

The interface between the cube textured Ni–W substrate, both bare and Pd-buffered, and the CeO2/YSZ buffer layer structure—required to growth YBCO coated conductors—samples have been subjected to different oxidizing conditions and have been investigated with different techniques: X-ray diffraction (XRD), X-ray absorption and Auger electron spectroscopy. Due to the Ni–Pd interdiffusion, the presence of a Pd over layer significantly modifies the substrate surface composition and the substrate oxidation mechanism. Depending on the Pd layer thickness, the formation of NiO can be completely prevented while the formation of ternary oxides and of W oxide is favored. Moreover, the Pd layer affects the extension of interface between the substrate and the CeO2 layer and the portion of uncontaminated CeO2. [ABSTRACT FROM AUTHOR]