YBCO Layer Research Articles

Enhanced current-carrying capability in YBCO coated conductor bilayers for high-field applications

We have investigated the impact of bilayer structures on the critical current density, J c, of YBa2Cu3O6+x (YBCO) coated conductor films, i.e. films grown on buffered metal substrates, under varying temperature and magnetic field conditions. The bilayers consisted of a YBCO layer free of artificial pinning centers and 8 wt% BaZrO3-added (BZO) layer on top, where the thickness percentage of the layers was varied from 0 to 100 %. The results reveal that the bilayer configuration enhances J c at temperatures below 60 K, with a significant improvement in high magnetic fields (5–8 T) and temperatures ≤20 K. The optimal BZO-added layer thickness was found to be approximately 70 %, reaching 80 % at 8 T. Structural examinations indicate improved growth of YBCO and BZO nanorods in the bilayer structure with BZO-added layer thickness ≤80 %. Theoretical model of the bilayer structure considering the layers as two parallel superconductors with different properties was developed. It was found that the model adequately explains all the experimentally observed tendencies, and thus the observed maximum in J c is due to better growth of the BZO-added layer. The study provides valuable insights for designing optimal bilayer structures for diverse applications operating in different temperature and magnetic field regimes.

Significantly Improving the Flux Pinning of YBa2Cu3O7‐δ Superconducting Coated Conductors via BaHfO3 Nanocrystal Addition Using Multistep Film Growth Method

AbstractA novel multistep film growth method is developed to prepare high‐performance BaHfO3(BHO)‐nanocrystal‐added YBa2Cu3O7−δ(YBCO) tapes. Upscaled YBCO tapes with high concentrations of 6.2 nm BHO nanocrystals exhibit better self‐field and in‐field performances when grown by the multistep method compared to those grown by the traditional method. The in‐field critical current (Ic) of the 1.6‐µm‐thick BHO‐added YBCO film at 30 K@3 T is enhanced by 50% in the optimal traditional cases, whereas it is further increased to 180% using a multistep growth strategy. The high‐performance YBCO layer is thickened to 2.3 µm using the multistep method, and the improvement of in‐field Ic at 30 K@3 T is enhanced by 215% to 360 A per 4 mm‐width compared to the pristine. The BHO size evolution during the high‐temperature process reveals that the added nanocrystals coarsened by 4 to 10.5 nm in both the traditional and multistep cases, thereby indicating that the further improvement in performance is attributed to the better film quality grown by the multistep method. This technique can be applied directly to the preparation of scaled REBCO tapes with a length of hundreds of meters.

Epitaxial growth and characterization of (110)-oriented YBCO/PBCGO bilayer and YBCO/PBCGO/YBCO trilayer heterostructures

We have grown and characterized (110)-oriented YBa2Cu3O7−x (YBCO)/PrBa2(Cu0.8Ga0.2)3O7−x (PBCGO) bilayer and YBCO/PBCGO/YBCO trilayer heterostructures, which were deposited by pulsed laser deposition technique for the nanofabrication of (110)-oriented YBCO-based superconductor (S)/insulator (I)/superconductor (S) tunneling vertical geometry Josephson junction and other superconductor electronic devices. The structural properties of these heterostructures, investigated through various x-ray diffraction techniques (profile, x-ray reflectivity, pole figure, and reciprocal mapping), showed (110)-oriented epitaxial growth with a preferred c-axis-in-plane direction for all layers of the heterostructures. The atomic force microscopy measurement on the top surface of the heterostructures showed crack-free and pinhole-free, compact surface morphology with about a few nanometer root mean square roughness over the 5 × 5 μm2 region. The electrical resistivity measurements on the (110)-direction of the heterostructures showed superconducting critical temperature (Tc) values above 77 K and a very small proximity effect due to the interfacial contact of the superconducting YBCO layers with the PBCGO insulating layer. Raman spectroscopy measurements on the heterostructures showed the softening of the Ag-type Raman modes associated with the apical oxygen O(4) and O(2)-O(3)-in-phase vibrations compared to the stand-alone (110)-oriented PBCGO due to the residual stress and additional two Raman modes at ∼600 and ∼285 cm−1 frequencies due to the disorder at the Cu–O chain site of the PBCGO. The growth process and structural, electrical transport, and Raman spectroscopy characterization of (110)-oriented YBCO/PBCGO bilayer and YBCO/PBCGO/YBCO trilayer heterostructures are discussed in detail.

Structural and magnetic anisotropy in YBa$_2$Cu$_3$O$_7$/La$_{0.67}$Sr$_{0.33}$MnO$_3$ bilayer on SrTiO$_3$ substrate

We study the magnetic properties and emergence of superconductivity in YBa_22Cu_33O_77 (YBCO)/ La_{0.67}0.67Sr_{0.33}0.33MnO_33 (LSMO) heterostructures. Bilayer films of superconducting layer, YBCO, and ferromagnetic layer, LSMO were grown on SrTiO_{3}3 (STO) (001) substrate using ultrahigh vacuum Pulsed Laser Deposition system. Magnetization data at 100 K as a function of applied magnetic field shows ferromagnetic behaviour due to the LSMO layer. Cooling below 100 K leads to superconductivity in this material; the onset of superconductivity occurs at a temperature, T_{c,SC},Tc,SC, of 86 K for H_{ext}\perp cHext⊥c (in-plane) & 84 K for H_{ext}||cHext||c (out-of-plane) under 100 Oe applied field. In-plane magnetic measurements show significant suppression of diamagnetic behaviour as compared to the out-of-plane measurements. The susceptibility signals are higher for out-of-plane direction. Such strong anisotropy in magnetism and the transition temperatures reveal complex interplay of magnetism and superconductivity in this system and calls for further study in this direction.

Magnetic Field Enhancement in Critical Current and Possible Triplet Superconductivity in LSMO/YBCO/LSMO Heterostructures

The large superconducting critical current (Ic) in superconductors is an important property for applications, but unfortunately, it is easily suppressed in the presence of a magnetic field. The stronger the magnetic field the lower the Ic is the common response of superconductors. In this paper, we discovered a phenomenon that the Ic can be enhanced by a field-cooled process for the La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7−δ (YBCO)/La0.67Sr0.33MnO3 (LSMO) trilayer system, in which the high-Tc-superconductor/oxide-ferromagnetic interface plays a crucial role. Three major factors based on a singlet superconducting picture, such as the difference in the work functions, the orbital hybridization, and the magnetic coupling between the induced Cu and Mn moments at the interface, decide the charge transfer and the capability of carrying maximum current. These factors can be preset by a field-cooling process with various field-cooled fields at a temperature higher than the superconducting transition temperature, Tc. While the system is field-cooled below Tc, we found that the competition between these factors and the responses of the interface may enhance or suppress the properties of the superconducting layer and finally gives rise to a maximum Ic at a specific field-cooled field. Moreover, we also observed that the Ic increases with the increase of the applied magnetic field for the sample with a thinner YBCO layer, which cannot be explained by these mechanisms based on singlet superconductivity and strongly implies the possible existence of triplet superconducting pairs at the interface and inside a ferromagnetic (FM) layer.

Preparation of Bi-2212/YBCO heterostructure and their interfacial characters

YBa 2 Cu 3 O 7-X (YBCO) thin films were prepared on LaAlO 3 (LAO) substrates by a sol-gel method, and the epitaxial growth of Bi-2212 thin films on YBCO thin films was investigated. Both YBCO and Bi 2 Sr 2 Ca 1 Cu 2 O 8+σ (Bi-2212) bilayer films exhibit good biaxial texture and superconducting properties. Afterward, a cross-shaped Bi-2212/YBCO heterostructure was fabricated, and its interfacial atomic arrangement and I - V characteristics were analyzed. Atomic-resolution STEM images obtained from a spherical-aberration-corrected transmission electron microscope show that two superconducting films exhibit a layered structure and the atoms inside the films are artfully arranged. Moreover, the order of the seven atomic layers between Bi-2212 and YBCO layers with a thickness of about 1.32 nm is misarranged. Among them, the Y-O layer of YBCO and the Sr-O layer of Bi-2212 share a CuO 2 layer. The I-V curves of Bi-2212/YBCO bilayer films show that the seven misarranged atomic layers at Bi-2212/YBCO interface acts as a barrier layer, which means that a Josephson junction can be fabricated using this interface characters.

Stress transfer mechanism and shear strength of multilayer composite superconducting tape

The interlayer stress transfer mechanism is the key to understand the delamination behaviour and determine the shear strength of multilayer composite superconducting tapes. Besides, it helps understanding the strain state of the superconducting material layer and further predicting its transport properties. In this paper, a theoretical model is established to investigate the stress transfer mechanism between layers of composite superconducting tapes. The stress distributions of a three-layer composite system are calculated based on the interlayer shear stiffness model. Then, the strain transmissibilities between different layers are further calculated considering the plastic deformation of the copper layer. Moreover, based on the proposed theoretical model, the shear strength of the composite superconducting tape is calculated. The model quantifies the stress transfer behavior between different layers of superconducting tapes, which provides the theoretical basis for the determination of the shear strength and suggests selecting a proper Hastelloy layer thickness can adjust the strain of the YBCO layer.

Defect Tolerant High-Temperature Superconducting Cable for the Central Solenoid of Compact Fusion Reactor

The future compact fusion reactors, will feature very high, >16 tesla, magnetic fields, which can be only created by magnet coils wound with the second generation (2G) superconducting wire. The 2G wires are currently manufactured with a thin (1-2 μm) YBCO layer deposited on a ~100 μm thick metal substrate. The substrate makes up a considerable portion of the cross-section, thus reducing the engineering current density. It also prevents effective inter-filament current sharing, and the wide tape geometry is responsible for high magnetization loss. We report on the recent progress in the development of a new type of high-temperature superconducting cable architecture for the central solenoid of a high-field fusion reactor. The new architecture combines two recent innovations: (i) Reduction of AC loss by bundling narrow, 1-2 mm, exfoliated YBCO filaments into a cable, (ii) continuous winding and parallel slicing technologies, which eliminate labor-intensive and expensive handling of narrow filaments, critical for the central solenoid, which operates under pulsed load.

Growth and characterization of La0.67Sr0.33MnO3/YBa2Cu3O7−δ bilayers

Understanding the interplay of ferromagnets and superconductors requires high quality interfaces. To this end, we have fabricated heterostructures of the cuprate superconductor YBa2Cu3O7−δ (YBCO) with the metallic ferromagnet La0.67Sr0.33MnO3 (LSMO) via pulsed laser deposition on SrTiO3 (STO) (001) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) (001) substrates. By varying the YBCO thickness from 1.7-13.6 nm while keeping the LSMO thickness at 12 nm, we have studied the interplay between ferromagnetism and superconductivity in the in-plane transport and magnetic properties of the bilayers. X-ray reflectivity data indicate the presence of a 2-3 nm thick interfacial layer between the LSMO and YBCO layers in all heterostructures. In-plane transport measurements exhibit suppression of the superconducting transition temperature from bulk YBCO values. Magnetometry measurements indicate high LSMO saturation magnetization values for samples grown on STO substrates and even higher (bulk-like) magnetization for bilayers grown on LSAT substrates. Together these results indicate that the interdiffused layer is largely attributed to a modified YBCO layer.

Texture of YBCO layer grown on GaN/c-sapphire substrates

YBCO thin films with epitaxial alignment were grown on (0001) oriented GaN/c-sapphire substrates using pulsed laser deposition. We performed a complete texture analysis and proposed a qualitative texture model explaining the measured X-ray pole figures of the YBCO films. The analysis revealed three texture components with the planes {001}, {113} and {207} parallel to the (0001) plane of the GaN surface. The six-fold symmetry of the GaN surface caused that all three texture components comprise six orientation variants. The orientation relationship of the variants with respect to the GaN/c-sapphire substrate was established. It was shown that thin MgO interlayer deposited on GaN/c-sapphire substrate before the growth of the YBCO layer can suppress the formation of the undesirable {113} and {207} texture components.

Multichannel Transmitting System Based on High-Temperature Superconducting Phase Shifter

Multichannel very high frequency (VHF) high-power transmission system, based on a 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , high-temperature superconductor YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (YBCO) hybrid coupler is presented. The small dimension coupler performs as a phase shifter utilized for matching several different channels into a single junction. The planar coupler was implemented in a microstrip geometry by patterning a thin layer of YBCO on a sapphire substrate. Superconductivity is essential for obtaining low losses and high-power capabilities. The system was tested for power transmission of up to 52.9 dBm over a period of several hours. No deterioration with time was recorded. Maximum losses of 0.8 dB per channel were measured. The proposed system shows high-precision tuning capabilities, a critical feature for multichannel systems.

Structural Analysis of 2G HTS Tapes under Different Loading Conditions for HTS Power Cable using Finite Element Modeling

In High Temperature Superconducting (HTS) power cable, HTS tapes are wound helically around a circular former and are subjected to different types of mechanical loads during manufacturing, transportation and installation of cable. The strain developed within the HTS tape during these processes may affect the superconducting properties of the tape. In the present work, 3D structural finite element (FE) models using ANSYS® are developed to obtain the strain behaviour of the tape under different loading conditions, considering the layered sandwich composite structure of 2G HTS tapes. The analysis is carried out with axial tensile and twisting loads on the tape, during helical winding of tape around the former and a combined effect of helical winding with external tensile and bending loads. The result obtained from FE simulation due to applied tensile load is compared with the established experimental result, which shows a good agreement. Further, the strain developed within the tape affects the critical current. Therefore, the strain is coupled with an empirical relation to obtain the critical current degradation of the tape. The FE analysis is carried out for five different winding pitches and four different bending radii with YBCO layer in the downward position and the corresponding critical currents are estimated. Further, a minimum winding pitch is obtained, below which the rapid degradation of critical current is initiated. The results show that the HTS tape with YBCO in downward position can withstand more amount of external load without affecting the critical axial strain of the tape.

On a Possibility to Fabricate YBCO Bridges with the Perfect Surface, Critical Temperature over 88 K and Critical Current Density up to 5 × 106 A/cm2

When manufacturing YBCO structures using traditional methods, a certain compromise is usually reached, namely: films with the relevant morphology, but with low electrophysical parameters are used. In this paper, it is shown that YBCO bridges 4 μm in width with the perfect surface morphology, i.e., without defects, with the critical current density Jc ≥ 3 × 106 A/cm2 at temperature 77 K and critical temperature Tc ≥ 88 K can be obtained using the master mask method. The perfect morphology of the bridge surface, values of the critical current density and critical temperature are retained even after the repeated (additional) deposition of the YBCO layer onto the structure with the master mask. The results obtained from the experiments with fifteen samples suggest that, unlike electrophysical characteristics, the fixation of the standard (basic) parameters of the growth process is not sufficient to obtain the perfect morphology of the YBCO film surface.

Rules of non-superconducting phase particles on crack propagation in YBCO coated conductors fabricated by the IBAD-MOCVD

Cracks caused by tensile stress in YBa2Cu3O7-x-coated conductors (YBCO-CCs) can cause irreversible degradation to their superconducting properties. Understanding the initiation and propagation modes of cracks can assist in preventing conductor failure and enhancing their mechanical properties in further. In this study, we used a chemical etching method and scanning electron microscopy to investigate crack morphology in the YBCO layer of conductors where the protective metal layer had been removed. For YBCO-CCs that experienced no deformation, many non-superconducting phase particles were observed and their grain size distribution corresponded to a Gaussian distribution. Energy dispersive x-ray spectroscopy identified these as Y-Cu-O particles. For the YBCO-CCs that experienced axial tension at 77 K, different propagation modes of cracks in the YBCO layer, including transgranular fracture, branching, deflection and pinning were observed for the first time. Statistical analysis demonstrated that transgranular fracture occurred in ∼ 95% of the crack modes. We analysed the reason for this phenomenon considering the thermal stresses stored inside and around the non-superconducting phase particles. The coefficient of thermal expansion of the Y2Cu2O5 particles is less than that of the YBCO superconducting matrix, and therefore, the hoop tensile stress generated near the boundary of the Y2Cu2O5 particle accelerates the bottom-up propagation of the crack. The other crack propagation modes such as crack branching, deflection, pinning and bridging in the YBCO layer can be considered mechanisms of blocking crack propagation that can increase the fracture toughness of the YBCO layer.

Photoresponse above 85 K of selective epitaxy grown high-Tc superconducting microwires

Superconducting single-photon detectors have become a very promising infrared photon counting technology. Utilizing high-Tc superconductors to implement photon counters is significantly more practical due to their much higher operating temperatures. We report photoresponse above 85 K of YBa2Cu3O7−δ (YBCO) microwires fabricated using selective epitaxial growth (SEG), demonstrating their high photon detection efficiency. SEG does not require post-deposition treatment of the YBCO layer, thus avoiding material damage and degradation, typically occurring in conventional submicrometer YBCO device fabrication. Our results show excellent superconducting performance with a Tc of up to 89 K and a sharp transition width of ΔT∼2 K, as well as a relatively high critical current density Jc of ∼5.7×105 A/cm2 at 77 K. The optical response of our YBCO microwires, especially the high responsivity of ∼3×103 mV/(nW/um2), paves the way for infrared single-photon detection using high-Tc superconductors.

Trilayer Films of YBa2Cu3O7−x/LaAlO3/YBa2Cu3O7−x with Superconducting Properties Prepared via Sol-Gel Method

The YBa2Cu3O7−x/LaAlO3/YBa2Cu3O7−x (YBCO/LAO/YBCO) heterogeneous trilayer film structures were prepared on the LaAlO3 (001) single-crystal substrate via the sol-gel method. The characteristics of the phase, orientation, and superconducting properties were studied via an X-ray diffractometer and a comprehensive physical property measurement system. The results show that when the LAO layer was thin (&lt;40 nm), the trilayer films were relatively pure and had a high c-axis orientation. When the nominal thickness of the LAO layer increased to 70 nm, non-c-axis oriented grains started to appear in the trilayer film. In this case, the top and bottom YBCO layers exhibited superconducting properties, and the resistance was found to be zero at 80.1 and 72.5 K, respectively. In addition, for the YBCO/LAO (40 nm)/YBCO structure, the intermediate LAO layer was too thin to completely cover the surface of the underlying YBCO. This resulted in point contact and micro-bridge contact in several micro-regions, thus forming a weak connection and exhibiting a current-voltage (I–V) characteristic similar to the direct-current (DC) Josephson effect. On the other hand, for the YBCO/LAO (70 nm)/YBCO structure, the thicker LAO layer could completely cover the underlying YBCO surface, which could isolate the superconducting current between the YBCO layers.

In Situ EBSD Study of Stable Cube Texture in an Advanced Composite Substrate Used in YBCO-Coated Conductors.

Advanced Ni8W/Ni12W/Ni8W alloy composite substrates used in YBCO-coated conductors with a strong cube texture and high yield strength have been fabricated, and a CeO2 buffer layer film was successfully deposited on the composite substrates. Through in situ tensile testing coupled with electron backscattered diffraction (EBSD) analysis, the stability of the cube texture of Ni8W/Ni12W/Ni8W alloy composite substrates has been investigated. The stress-strain curve shows that the yield strength (at 0.2% strain) of the composite substrates exceeds 250 Mpa. The orientation of grains and boundaries on the surface of the substrates was almost unchanged, while the strain exceeds 0.2%, which indicated that the composite substrates are adequate for depositing buffer layers and YBCO layers by the reel-to-reel process.

Homogeneity in the Microwave Surface Resistance of Large YBa2Cu3O7−δ Superconductor Films Coated with Au

We studied homogeneity in the microwave surface resistance of Au-coated YBa2Cu3O7−δ (Au/YBCO) films. The Au/YBCO film with 4-inches in diameter was prepared in-situ with the thicknesses of 68 nm and 365 nm for the Au layer and the YBa2Cu3O7−δ (YBCO) layer, respectively. We measured the effective surface resistance (RS,eff) of the Au/YBCO film at temperatures of 25 K, 60 K, 70 K, and 77 K, respectively, at 29 different positions on the film. The RS,eff values were analyzed with the finite thicknesses of the Au and the YBCO layers taken into consideration. The local RS,eff values of the Au/YBCO film appeared to be almost uniform at 25 K. Meanwhile significant positional dependences were observed for the RS,eff of the Au/YBCO film at 60 K, 70 K and 77 K, respectively, which seemed to be due to non-uniform local penetration depth (λ) of the YBCO layer rather than due to variations in the local real-part conductivity of the YBCO layer. The observed results could not be attributed to the properties of the Au layer. At temperatures below the critical temperature of YBCO, the observed RS,eff values of the Au/YBCO film were significantly lower than those estimated using the surface resistance of Au and YBCO, which reflected proximity effects of the normal-metal Au layer in contact with the superconducting YBCO layer. Homogeneity in the RS,eff of the Au/YBCO film might be correlated with the distributions in the local λ of the YBCO layer, providing valuable information needed for designing microwave filters.

Magneto-transport in La2/3Sr1/3MnO3/YBa2Cu3O7/Alq3/Co spin-valves

We studied how an additional layer of the high superconductor YBCO affects the magneto-transport across a LSMO/Alq3/Co spin-valve structure. We found that up to a thickness of at least 10 nm the YBCO layer on top of LSMO hardly changes the spin-valve effect, since the device resistance still depends on the relative orientation of the LSMO and Co magnetization. The spin-valve effect persists even when the superconducting YBCO layer acts as bottom electrode, with no spin-polarized current injected from LSMO into YBCO. This highlights that the charge carriers of a thin YBCO layer on top of LSMO are strongly spin-polarized, most likely due to a magnetic proximity effect involving a transfer of spin-polarized electrons from LSMO to YBCO. Evidence for a strongly underdoped state of the YBCO layers close to the interface with LSMO is indeed obtained from the dI/dV curves in zero magnetic field which reveal a pseudogap persisting well above .

О возможности изготовления мостиков YBCO с совершенной поверхностью, критической температурой более 88 K и плотностью критического тока до 5&amp;#183;10-=SUP=-6-=/SUP=- A/cm-=SUP=-2-=/SUP=-

In the fabrication of YBCO structures by traditional methods, as a rule, some compromise is reached, namely, films with acceptable morphology are used, but with reduced electrophysical parameters. In this paper, it is shown that YBCO bridges up to 4 microns wide with perfect surface morphology, i.e. free from defects, with a critical current density Jc ≥ 3106 A/cm2 at a temperature T = 77 K and a critical temperature Tс ≥ 88 K. can be obtained using the preliminary topology mask method. Moreover, the perfect morphology of the bridge surface, the values of the critical current density and the critical temperature are preserved even after repeated (additional) deposition of the YBCO layer on the structure with the preliminary topology mask. Based on the results obtained in a series of fifteen samples, it is concluded that, in contrast to the electrophysical characteristics, it is not enough to fix the standard (basic) parameters of the growth process for the stable implementation of the perfect surface morphology of YBCO films.