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Fusion power plants offer the prospect of a new sustainable source of energy for future generations. The design and R&D of future reactors is expected to largely benefit from the experience gained in the design, construction and operation of ITER. However, deploying reliable fusion power plants, requires to overcome the design challenges and to address the remaining readiness gaps. Europe is starting the Conceptual Design Phase for building a superconducting DEMOnstration Fusion Power Plant (DEMO) and starting operations around the middle of the century. The aim is demonstrating the production of 500 MW of net electricity, with a closed tritium fuel cycle and adequate plant availability. For the design of the Superconducting Magnet System several variants of coils have been investigated in the pre-conceptual design phase, which has concluded in 2020. Some of them are very close to ITER design, therefore have a relatively high technology readiness level. The 'alternative' proposed solutions, that are very promising in terms of costs and performances, need a validation to industrial scale in order to be eligible for the down-selection expected in 2024. In particular, the validation regards the design of the layer-wound graded TF winding pack based on React-and-Wind Nb3Sn conductors, and the hybrid, layer-wound graded CS coil. The challenging aspect is that the CS magnet is made of REBCO conductors in high-field, React-and-Wind Nb3Sn conductors in medium field and NbTi conductors in low field. Also innovative techniques need to be studied for insulating critical parts of the coils, as penetrations, discontinuities and joints. The main issues of the technological development are illustrated. A R&D work plan is presented for the Conceptual Design phase to validate the technology within 2024 and demonstrate the operational capabilities by testing superconducting insert coils, that is about 50-m long wound conductors, by 2027

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.

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.

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.

A higherature superconducting (HTS) cable-in-conduit conductor (CICC) suitable for high-field magnet applications and comprised of twisted-stacked coated-conductor tapes arranged around a helically slotted core has been recently proposed and tested, demonstrating full compatibility with existing cabling technologies. To form the desired shape of any coils for high-field magnet applications, any suitable CICC option needs to be bent. For a magnet design, it is then very important to characterize the bending behavior of the CICC and, in particular, to find the smallest bending radius achieved without performance degradation. To this aim, bending tests were carried out on 1-m-long dummy samples of five helical slots in an extruded aluminum core, in which four REBCO tapes and dummy stainless-steel tapes were mounted in each slot. A controlled bending moment has been applied to the HTS CICC samples at room temperature, and each individual superconducting tape has been electrically characterized as a function of bending radius by measuring the critical current and $n$-index values at 77 K in a self-field condition. Results are analyzed and explained with the help of a three-dimensional cable model implemented in ANSYS and analytical calculations. The experimental and numerical results presented in this paper will demonstrate that the twisted-stack slotted-core technology can meet the bending requirements of high-field magnet designs. © 2002-2011 IEEE.

Superconducting YBa2Cu3O7-δ films with different amounts of BaZrO3 nanoinclusions were deposited on SrTiO3(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.

ENEA is currently involved in the design and manufacture of a fully high temperature superconductor (HTS) cable in the cable-in-conduit conductor (CICC) configuration exploiting commercial second generation ReBaCuO (Re: Rare Earth and Y) coated-conductors. The final cable will be composed of five slots obtained in a helically twisted aluminum central core and filled with 2G tape stacks. This conductor is designed to operate above 10 kA in 12 T background field at 4.2 K or at about 10 kA in self-field at 77 K. A first sample of about 1-m length with one fully superconductive slot has been manufactured using 15 tapes provided by Superpower, Inc. and 12 tapes from the SuNAM Company grouped in two sub-stacks divided by a Kapton foil. Each tape of the stack has been characterized individually by measuring critical current values Ic at 77 K (liquid N2 bath) in self-field and n-index. Results revealed that the tapes showed no degradation of critical current values when compared with suppliers specifications confirming that the proposed manufacturing process is fully compatible with commercial coated-conductors. Inter-tape resistance (Rinter) has also been measured and the observed dependence of Rinter on the tape position in the stack has been put in correlation with transverse stress distribution calculated by finite element models. A second sample with a full superconducting slot has been manufactured using 18 SuNAM tapes. Preliminary results on the stack transport measurements performed at 77 K in self-field will be presented and discussed. All the samples were manufactured by using already existing industrial equipments at Tratos Cavi SpA. © 2014 IEEE.

A detailed study on YBa(2)Cu(3)O(7-delta) (YBCO) films with BaZrO(3) (BZO) inclusions (YBCO-BZO) deposited on SrTiO(3) substrate with different BZO contents is presented. X ray diffraction, SEM imaging and superconductive critical temperature (T(c)) measurements were performed to evaluate film growth quality. Independently from the BZO content, all YBCO-BZO films showed T(c) values close to that of pure YBCO indicating that the T(c) 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 (J(c)) dependence on magnetic field if compared to the typical J(c)(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 J(c)(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. J(c)(B) recorded at several temperatures down to 10 K revealed matching effect features.

We perform measurements of high-frequency (similar to 48 GHz) microwave surface impedance with an applied magnetic field in YBa(2)Cu(3)O(7-delta) ( YBCO) laser-ablated films with various amounts of BaZrO(3) ( BZO) sub-micrometric inclusions, up to 7 mol % concentration. BZO inclusions are very effective in the reduction of the field-induced surface resistance in our experimentally accessible field range [ 0, 0.8] T. At temperatures low enough, the application of a moderate (similar to 0.2 T) field makes the YBCO/BZO films markedly less dissipative than pure YBCO. This result, examined in the light of the very high measuring frequency ( very small vortex oscillation amplitude) shows that BZO inclusions are even more effective pinning centers than columnar defects. We study the dependence of the vortex parameters ( vortex viscosity, pinning constant) on the BZO concentration. We examine the correlation between the reduction of the microwave dissipation and the areal density of BZO-induced defects. We argue that the very improved performances in a magnetic field are due to individual pinning of vortices on BZO inclusions.

Axial flux electrical machines (AFEM) with shaped disk structure increases the power-to-weight ratio using HTS materials. The introduction of permanent magnets on rotor disk and of superconducting coils on stator disk, instead of conventional field and armature winding, respectively, allows the development of lighter, more compact, and more performing AFEM. In this paper, we report the electromagnetic properties of an HTS coil in a double pancake configuration measured at LN2 temperature. Also, simulation studies by means of finite element and constant lumped models are reported. Commercial grade ReBa2Cu3O7-x (Re = Y or rare earths, ReBCO) tape and epoxy resin have been used for coil winding. The combination of experimental and simulation results allow ac losses, in the HTS coils used in an all-superconducting machine design, to be estimated.

In this paper, YBCO-based commercial wire (tape) has been used for fabricating coils in doubled pancake configuration assembly. The tape has been wound on a circular-shaped support; lap joints between coils have been realized with particular attention to resistance minimization. Each high-temperature superconducting coil by itself, and the assembly afterward, has been powered and the current-voltage curves at different temperatures have been measured using a four-probe technique. Critical currents have been computed by using the electric field criteria. Applied magnetic field was both in perpendicular and parallel configuration. A magneto-static finite element model has been developed by using commercial software, in order to check the agreement with experimental results. © 2013 IEEE.

Superconducting strips coated with boron were engineered with a view to subnuclear particle detection. Combining the characteristics of boron as a generator of α-particles (as a consequence of neutron absorption) and the ability of superconducting strips to act as resistive switches, it is shown that fabricated Nb-boron and NbN-boron strips represent a promising basis for implementing neutron detection devices. In particular, the superconducting transition of boron-coated NbN strips generates voltage outputs of the order of a few volts thanks to the relatively higher normal state resitivity of NbN with respect to Nb. This result, combined with the relatively high transition temperature of NbN (of the order of 16 K for the bulk material), is an appealing prospect for future developments. The coated strips are meta-devices since their constituting material does not exist in nature and it is engineered to accomplish a specific task, i.e. generate an output voltage signal upon α-particle irradiation. © 2016 IOP Publishing Ltd.

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 μm. Epitaxial MgO films were deposited by e-beam evaporation at 400 °C 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.

We performed an extensive characterization of Co-doped polycrystalline 122 iron pnictide samples, Ba(Fe1-xCox)2As2 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.

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.

Ni–Cu–Co alloys were studied for the development of textured substrates for YBCO-coated conductor application. Three compositions were obtained by adding a fixed amount of 3 at.% Co to the binary NixCu100−x, where x = 40, 50 and 60. Cube texture was induced by conventional cold rolling followed by high-temperature annealing. The structural, microstructural, morphological, electrical, magnetic, mechanical and oxidation properties were evaluated and compared with those exhibited by the binary Ni–Cu alloy, as well as by Ni–W and pure Ni. A low Ni content is detrimental for the development of the cube texture with respect to higher concentrations. Nevertheless, the use of high annealing temperatures enabled an area fraction of cube orientation as high as 95% to be obtained for x = 40, and >97.5% in the case of Ni-richer alloys. Compared with Ni and Ni–W, Ni–Cu–Co alloys oxidize more easily and exhibit higher electrical resistance. In addition, the presence of copper enables the Curie temperature to be reduced to 60 K for x = 40 and to 155 K for x = 50. Furthermore, the introduction of cobalt reduces the oxidation rate at temperatures normally used for the deposition of ceramic buffer layers, thus allowing the successful development of a CeO2/YSZ/CeO2 architecture on ternary Ni–Cu–Co alloy. YBCO/buffer multilayer architecture deposited by pulsed laser deposition on a selected alloy tape exhibits a critical current density exceeding 1 MA cm−2 at 77 K in self-field, indicating that this alloy substrate is suitable for YBCO-coated conductor application.

Ni48.5Cu48.5Co3 alloy was studied for the realization of cube-textured substrates for YBCO coated conductors. The small amount of Co was added in order to improve the microstructure as well as the mechanical properties of the binary Ni-Cu alloy. Structural, microstructural and morphological characterizations have been carried out in order to evaluate the suitability of this substrate as a template for YBCO coated conductor application. A cube area fraction as high as 97.7% was obtained after annealing for 30 minutes at 1050degC. Further, mechanical, magnetic and electrical properties have been studied and compared with those exhibited by other Ni-based alloys. The standard CeO2/YSZ/CeO2/YBCO multilayer architecture was deposited on Pd-buffered substrate by means of PLD and characterized in order to verify the suitability of this template for YBCO coated conductor application. The obtained YBCO film is adherent, well textured with an out-of-plane distribution of 4.1deg (FWHM) in rolling direction and good superconducting properties with a critical temperature of about 88 K and a critical current density of 1 MA/cm2. The obtained results demonstrate that this alloy tape is a good candidate for the production of YBCO-based coated conductors.

A new modified TFA-MOD method for the YBa2Cu3O7-x (YBCO) deposition, using only barium trifluoroacetate, is presented. The yttrium and copper trifluoroacetates were replaced by the alcoholic solutions of Cu and Y acetates dispersed in propionic acid to prepare a stable coating solution. Due to the smaller amount of evolved hydrofluoric acid, this method permits the shortening of the pyrolysis time by a factor 4, with respect to conventional trifluoroacetate metal organic deposition (TFA-MOD) method. The X-ray photoelectron spectroscopy (XPS) analyses, performed on a pyrolyzed sample, showed the complete decomposition of precursors. The as obtained films exhibit good morphological, structural and superconducting properties with T c(R = 0) greater than 90 K. Transport measurements at different temperatures and applied magnetic fields have revealed promising superconducting properties of the critical current density (J c) vs. the applied magnetic fields and the value of J c at 77 K and zero magnetic field greater than 3 MA/cm2.

Extensive applications of YBCO tapes claim for a comprehensive knowledge of their behavior in every possible operating condition. In particular, one of the main topics to explore is the tape stability against heat and current disturbances, in terms of minimum quench energy and normal zone propagation velocity (NZPV). In this work we present the results of NZPV measured in a 35 cm long YBCO coated conductors manufactured by SuperPower Inc. The tape is cooled by means of a cryocooler and kept under vacuum in order to achieve near-adiabatic conditions. Two independent heaters are positioned on the tape: one on the YBCO side and the other on the substrate side. The quench is monitored by recording the voltage and the temperature evolution along the tape. The NZPV, at 77 K, reaches a value larger than 2.5 cm/s for a bias current I=50 A which represents the 56% of the critical current value. The quench dynamics of the tape are discussed with the help of a simulation program based on the finite difference discretization of the tape with the Fourier's heat equation: the model is able to reproduce the experimental behavior.

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 75divide80 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.

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 $\eta$, the pinning constant k_p and the upper limit for the creep factor \chi_M. We show that the directional effect of the nanorods is absent in \eta, which is dictated by the mass anisotropy \gamma. 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., Comment: Proceedings of VORTEX VIII Conference, to be published in Physica C

La2Zr2O7 (LZO) film grown by the chemical solution deposition (CSD) technique is a widely studied buffer layer for YBa2Cu3O7-x film growth on a rolling-assisted biaxially textured (RABiT) substrate. A biaxially textured LZO film is epitaxially grown on a cube-textured metal substrate. In a RABiT substrate, cube texture is obtained as primary recrystallization of heavily cold-rolled fcc metals and is normally developed before CSD film deposition to obtain an oriented film growth. In this paper, we show that a biaxially textured LZO film can be grown by depositing the precursor solution directly on a cold-rolled fcc metal substrate and performing a single heat treatment. In fact, we show that if the recrystallization temperature of the metallic substrate is lower than the nucleation temperature of the film, a biaxially textured film is obtained as a result of transient cube texture transfer. Biaxially textured LZO films grown on cold-rolled substrates are compared with films grown on recrystallized substrates. In particular, the growth of LZO on either pure-Cu- or Ni-based substrate was studied. Compared with the LZO film grown on a cube-textured substrate, LZO grown on a cold-rolled substrate shows similar structural properties and morphology. Moreover, films are well adherent without cracks or delamination, suggesting that grain boundary migration in the metallic substrate has no detrimental influence on the film. In some cases, secondary recrystallization of the substrate occurs, without affecting the quality of the LZO film. © 2016 IEEE.

The proposed study investigates the aging of two precursor solutions used for the chemical solution deposition of YBa2Cu3O7-x (YBCO) and composite YBCO films with nanostructured inclusions of BaZrO3 (YBCO-BZO). The stability of precursor solutions plays a crucial role in determining the crystalline quality and the superconducting properties of YBCO films. Although low- or free-fluorine solutions are promising in order to improve the synthesis route and to reduce the environmental impact, the poor stability of the solution is the major drawback of the low-fluorine precursors since they degrade faster (4-6 weeks) than other precursor solutions for superconducting layers (e.g., trifluoroacetates solutions are stable up to 6 months) or buffer layers (stable for several months). Therefore, a deeper comprehension of the degradation mechanisms is fundamental to properly optimize the composition of the precursor solution. The current work studies two precursor solutions (for YBCO and YBCO-BZO) that are complex systems, in which different interactions need to be considered: most of all, the nature of ligands (acetate, propionate, ammonia) that complex each metal and influence not only the solution stability but also the quality of the deposited film. Thus, information obtained from different analyses is correlated with morphological, structural, and superconducting properties of the deposited film in order to understand the underlying chemical mechanisms of aging (salts precipitation, oxidation, polymerization) and its effects. © 2002-2011 IEEE.

The transport properties of nanocomposite YBa 2 Cu 3 O 7-x (YBCO) films grown by metal-organic decomposition (MOD) and prepared with a low-fluorine-coating solution on SrTiO 3 single-crystal substrates were studied with dc and microwave measurement techniques. As demonstrated in previous studies, the combination of these two techniques is a powerful tool for vortex pinning investigation. The BaZrO 3 inclusions (BZO) as artificial pinning centers were introduced into the YBCO matrix by the excess of corresponding Ba and Zr precursor salts to the initial YBCO precursor solution up to 5 mol%. The effect of BZO was clearly observed in magnetic field dependence relations of critical current density (J c ) and the complex surface impedance, i.e., ΔZ, at fixed temperature and magnetic field parallel to the c-axis. The result shows that BZO particles mainly act as isotropic pinning centers. The short-range vortex dynamics was probed by the ~47.7-GHz microwave surface impedance technique. The derived vortex parameters r and k p were sensitive to the presence of nanoparticles, indicating the effect of BZO on pinning. The joint field dependence relations of J c and k p help in elucidating the pinning regime in our nanocomposite MOD YBCO/BZO films.

A REBCO coil system for axial flux electrical machines applications is presented. Three couples of series-connected coils have been placed on a fiberglass disc and wired in star configuration to simulate a three-phase, ironless, and superconducting armature concentrated winding. REBCO-based commercial tape has been used to wind each of the six coils in double-pancake configuration around a fiberglass trapezoidal-shaped core. DC current-voltage curve and ac transport current losses plots of each coil have been obtained at liquid nitrogen temperature. Six copper coils having the same shape and geometric parameters of REBCO coils have been also manufactured to assemble a conventional armature concentrated winding. Laboratory testing on different armature windings has been conducted at different temperatures (77 K and 300 K) to measure the impedance (amplitude and phase) value, the back electromotive forces waveform, etc. The experimental results of both configurations (conventional and superconducting) are compared to study the feasibility of a superconducting armature winding prototype of an axial flux electric machine. © 2002-2011 IEEE.

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 is 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.

The addition of artificially induced defects improves the pinning efficiency of magnetic flux vortices in YBa2Cu3O7-delta (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 I mu m. 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. De electrical transport measurements at 77 K have revealed a better magnetic field retention of the critical current density, J(c) 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.

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 CeO 2 buffered substrates, has been ascribed to elongated defects along the c -axis of the film. In order to evaluate the role of calcium and CeO 2 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 10 at.% Ca substituted YBCO grown on CeO 2 buffered Al 2 O 3 single crystal substrates. Results are compared with data obtained on 10 at.% Ca substituted YBCO grown on SrTiO 3 single crystal substrate.

We report on the superconducting properties of epitaxial thin films Y/sub 1-x/Ca/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-y/ with 0/spl les/x/spl les/0.2, grown on SrTiO/sub 3/ [001] by Pulsed Laser Deposition (PLD) technique. The partial substitution of Ca/sup 2+/ at the Y/sup 3+/site in YBCO leads to a monotonic decrease of the zero resistance critical temperature, T/sub c/. The oxygen stoichiometry is varied by means of post-deposition thermal treatment varying the oxygen partial pressure. The dependence of T/sub c/ on annealing oxygen pressure can be attributed to an overdoping effect and/or to a cation disorder.

A CeO/sub 2//YSZ/CeO/sub 2/ buffer layer structure was epitaxially deposited by pulsed laser deposition on a Pd seed layer grown on non magnetic Ni/sub 88/Cr/sub 8/W/sub 4/ alloy. Structural analyzes performed by x-ray diffraction and EBSD show a good texture, with typical YBCO FWHM of about 5/spl deg/ and 8.5/spl deg/ for in-plane and out-of-plane orientations, respectively. About 300 nm YBCO films deposited by PLD on such a buffer layer structure, show typical values of critical temperature of about 89 K and a critical current density greater than 0.6 MA/cm/sup 2/ at 77 K and self field.

We investigate the effect of partial substitution of Y by Ca in YBCO superconducting thin films. The films were grown on (1 0 0) SrTiO 3 single crystal substrates by pulsed laser deposition (PLD). The Ca doped film were ablated from Y 1− x Ca x Ba 2 Cu 3 O 7− 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.

The formation and characterization of MgB/sub 2/ thin films is explored, using room-temperature deposition of precursor layers and subsequent annealing in-situ. Precursors were deposited by means of pulsed laser deposition (PLD), electron beam (EB), and sputtering (SD) techniques. Best results were obtained for B/Mg multilayers deposited by EB and annealed at 630/spl deg/C for 10 minutes, showing typical T/sub Con/ and T/sub C0/ values of about 32-34 K and 31-32 K, respectively. Structural and morphological analyses were performed by x-ray diffraction and SEM. A comparison among the different growth techniques is presented. Results are explained taking into account the pressure-temperature phase diagram of the Mg-B system.

The microstructure of Ni-5at%W (Ni-W) and Ni-11at%V (Ni-V) biaxially textured substrates has been investigated using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The correlation between the substrate microstructure and superconducting transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) film grown on it has been studied on the YBCO/CeO/sub 2//Ni-W and YBCO/CeO/sub 2//NiO/Ni-V architectures. Our study has ascertained that the in-plane texture of the substrates is one of the most important factors, limiting the critical current density. The Ni-V substrate has a lower percolation area due to the larger number of twinned grains and a broader in-plane angular distribution and, as a consequence, the YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) film grown on it has a critical current density of 0.6 /spl times/ 10/sup 6/ A/cm/sup 2/, depressed by factor 2 with respect to YBCO grown on the Ni-W substrate. For the Ni-V substrate, another limiting factor is its low oxidation resistance. In contrast to Ni-V, the Ni-W substrate has a larger percolation area, mainly due to the absence of twinned grains, and a high oxidation resistance.

A YBa2Cu3O7-δ (YBCO) film grown by metal organic decomposition (MOD) is a promising candidate in the realization of high-performance superconducting wires with high critical current density. Moreover, artificial pinning centers (APCs) inclusions improve the current transport performance of the films in both high magnetic fields and temperatures. © 2015 IEEE.

Biaxially aligned YBa2Cu3O7−δ (YBCO) thick films were deposited by pulsed laser ablation technique on cube textured non-magnetic Ni89V11 (Ni–V) substrate, using CeO2/YSZ/CeO2/NiO buffer layer architecture. The first NiO seed layer was formed by epitaxial oxidation of the Ni–V substrate. Structural analyses show typical full width at half maximum values of φ- and ω-scans less than 10° and 8°, respectively. The highest value obtained for the critical current density at 77 K and zero magnetic field was 6×105 A cm−2, which is close to that obtained for YBCO films grown on CeO2/NiO buffer layer architecture.

The epitaxial oxidation of the (0 0 1)[1 0 0] textured Ni100−xVx tapes was studied because of the practical interest of NiO as a first buffer layer for the YBCO based coated conductors. The study revealed that the oxidation of the Ni–V alloy is rather complex, the less noble V being internally oxidized, while Ni undergoes an external oxidation. Moreover, the formation of the NiVO3 and of Ni7V5O17 compounds have negative effects on the epitaxial oxidation and on the surface morphology, as well. The role of vanadium on the epitaxial oxidation of Ni–V alloy has not been fully understood yet. The optimum conditions for the epitaxial oxidation have been found to be: 700 ° C, t

Biaxial cube texturing and surface quality of the metallic substrate are key parameters for high J c coated conductors. Experiments have demonstrated that the sharp cube texture can be developed up to 11 at.% V, 12 at.% Cr and 5 at.% W alloys; the respective cube textured area fractions result to be 96%, 97% and 99%. For all the studied alloys, FWHM values of ω - and φ -scans are in the range of 5–6° and 6–8°, respectively. Microstructural analyses reveal smooth surfaces with grooves localized at the grain boundaries of twinned cube textured and misoriented grains.

We report photoluminescence spectra of C60 single crystals grown by vapor phase transport method using either the sealed ampoule technique or the open tube technique. The spectra for both types of samples show similar features, but different line resolution related to the two different growth techniques. An analysis of temperature and excitation intensity dependencies of the luminescence spectra is reported. The main structures of the spectra have been interpreted according to a model involving intramolecular polaron-exciton recombinations. In particular, emissions due to purely electronic transitions of singlet and triplet or the exciton and related vibronic recombinations have been resolved. At low temperature, emission bands due to X-traps have been observed on the high-energy side of the excitonic singlet purely electronic transition.

A promising approach to improve the engineering current density of coated conductors is to increase the thickness of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) layer. In this framework, a study regarding the relationship between the thickness of the superconducting film and its critical current was performed on biaxially aligned YBCO films grown on epitaxial Ce/sub 2/O/NiO structure using Ni/sub 89/V/sub 11/ non-magnetic substrate. The critical current density (J/sub C/) was measured for a series of YBCO films with thickness ranging from 0.2 to 2 /spl mu/m, deposited at constant rate. J/sub C/ values up to 6.4/spl times/10/sup 5/ A/cm/sup 2/ at 77 K and zero magnetic field were obtained for thinner films decreasing three orders of magnitude for the 2 /spl mu/m thick YBCO film. X-ray diffraction and morphological analyses indicate a progressive structural deterioration with the increase of film thickness.

YBa 2 Cu 3 O 7− δ thin films with BaZrO 3 (BZO) inclusions have been deposited on SrTiO 3 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 J C retention in applied magnetic field and, for higher temperatures, the appearance of correlated pinning contribution, as confirmed by pinning force density measurements.

We analyze the voltage–current characteristics of high quality c -axis oriented YBa 2 Cu 3 O 7− δ films with T c0 ≈91 K. The films were dc sputtered in a pure oxygen atmosphere on SrTiO 3 (1 0 0) substrates and then patterned in a shape of a long strip. The voltage–current characteristics are modeled with single or multiple Gaussian distributions of depinning currents. We derive the distribution features as a function of the applied magnetic field at different temperatures.

We probe the short-range pinning properties with the application of microwave currents at very high driving frequencies (47.7 GHz) on YBa$_2$Cu$_3$O$_{7-\delta}$ films with and without sub-micrometer BaZrO$_3$ inclusions. We explore the temperature and field ranges 60 K$, Comment: 4 pages, pdfTeX, presented at VORTEX Conference, to appear on Physica C

This paper presents the development of the CeO/sub 2/ buffer layers on both the non magnetic Ni-V and the Pd-buffered Ni substrates by pulsed laser ablation (PLD). The CeO/sub 2/ films show strong in-plane and out-of-plane orientations. The SEM studies showed that the CeO/sub 2/ films are both smooth and continuous. The magnetic and structural properties of the new Ni-V substrate are also presented. The results demonstrate that Ni-V is an alternative substrate for the fabrication of textured YBCO conductors.

Taking advantage of the large experience of the ENEA Superconducting Laboratory in the manufacture and characterization of large scale superconducting systems, a project was launched, aimed at using High Temperature Superconductor (HTS) 2G wires for the manufacture of a cable-in-conduit conductor (CICC). In particular, the main aim was the definition of a conductor design fully compatible with existing cabling technologies, to be promptly transferred to an industrial scale production. The considered layout is based on 150 HTS tapes, arranged as five layered structures of twisted tapes wound on a helically slotted core with external round jacket. All manufacturing steps (slotted core production, tape stacking and insertion into the ducts, external wrapping and jacketing) are fulfilled by using equipments and technologies available at TRATOS Cavi S.p.A. These CICCs are intended for operation using forced flow of Helium. A 2D local thermal model has been developed for the optimization of the cooling configuration. This conductor is designed to target 20 kA at 4.2 K and 15 T (or, alternatively, higher temperature, in self-field and LN2 cooling) corresponding to a Je of about 55 A/mm2. The production of a short dummy sample revealed that the exploited industrial production process is very promising for the development of HTS CICC. © 2013 IEEE.

In the present paper, we analyze the role of in situ grown BaZrO3 (BZO) inclusions in YBa2Cu3O7−x (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 c (𝜃), 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 c , 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 c , of the YBCO host is measured, in self-field at 77 K, corresponding to a value of J c =2.9MA/cm2, whereas a factor 10 is measured at 1 T (J c =0.35 MA/cm2).

The paper presents the growth and characterization of highly textured La 2 Zr 2 O 7 (LZO) multilayer coatings on Ni–5 at.%W (NiW) biaxially textured substrates by chemical solution deposition (CSD) under highly reducing conditions (Ar + 12%H 2 ) in order to protect the metallic substrate from oxidation. The coating solution consists in a stoichiometric mixture of lanthanum and zirconium acetylacetonates dissolved in an excess of propionic acid. The precursor chemistry was studied by means of infrared spectroscopy, thermogravimetric–differential thermal analyses, Raman spectroscopy and X-ray diffraction carried out on the precursor powder. The as-grown multilayer LZO coating exhibits a sharp in-plane and out-of-plane texture, with the full-width-at-half-maximum of the ω -scans and φ -scans of about 7.2° and 8.0°, respectively, close to that of the NiW substrate. The volume fraction of the c -axis oriented grains from the top layer of the coating increases with the number of layers. The LZO coating exhibits a smooth and crack-free surface, appropriate for the further epitaxial growth of a seed layer for the YBa 2 Cu 3 O 7 − x (YBCO) deposition. Transmission Electron Microscopy was used to investigate the microstructure of the CSD LZO thin films deposited on flexible NiW substrates. A high density of nanovoids, with a size ranging between 10 and 30 nm, was observed in the LZO layers. YBCO films epitaxially grown by pulsed laser deposition on the CSD LZO buffer layer exhibit critical current densities, J c , close to 1.6 MA/cm 2 at 77 K and self-field and zero resistance critical temperature ( T c (R = 0)) of 90.3 K.

We present a microwave study of the angular dependence of the flux-flow resistivity $\rho_{ff}$ 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 $\rho_{ff}$ is a scaling function of a reduced field $H/f(\theta)$. We extend a model for the anisotropic motion of vortices in uniaxially anisotropic superconductor, able to describe the experimental $f(\theta)$ 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$^{\circ}$, 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., Comment: 5 pages, 3 figures