Μm Thick YBCO Films Research Articles

The Influence of Temperature Distribution on YBCO Coated Conductor Deposited by Reel-to-Reel PLD Method

It is known that the tape’s temperature controlled by a close substrate heater will still deviate after the deposition process. In this work, we deposited YBa2Cu3O7−δ(YBCO) films on RABiTS substrates with multilayer CeO2/YSZ/CeO2 buffer layers by pulsed laser deposition (PLD) under a different distribution of temperature deviation in order to improve it. Thermocouples were applied to exactly measure the temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to inspect c-axis oriented crystals and surface morphology of YBCO films. Through this work, we found that the even shape is best. Under the temperature deviation with the best shape, a transport Jc of 3.2×106 A/cm2 and Ic=240 A was obtained for a 0.75 μm thick YBCO film on CeO2/YSZ/CeO2-bufferd RABiTS Ni–W alloy.

Modified Lanthanum Zirconium Oxide buffer layers for low-cost, high performance YBCO coated conductors

Abstract The pyrochlore Lanthanum Zirconium Oxide, La2Zr2O7 (LZO), has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni–5%W metal tape. The main focus of this research is to ascertain whether: (i) we can further improve the barrier properties of LZO; (ii) we can modify the LZO cation ratio and still achieve a high level of performance; and (iii) it is possible to reduce the number of buffer layers. We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La2O3–ZrO2 system. Using a metal–organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of LaxZr1−xOy (x = 0.2–0.6) on standard Y2O3 buffered Ni–5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase with only (0 0 1) texture can be achieved in a broad compositional range of x = 0.2–0.6 in LaxZr1−xOy. Both CeO2 cap layers and MOD–YBCO films were grown epitaxially on these modified LZO barriers. High critical currents per unit width, Ic of 274–292 A/cm at 77 K and self-field were achieved for MOD–YBCO films grown on LaxZr1−xOy (x = 0.4–0.6) films. These results indicate that LZO films can be grown with a broad compositional range and still support high performance YBCO coated conductors. In addition, epitaxial MOD LaxZr1−xOy (x = 0.25) films were grown directly on biaxially textured Ni–3W substrates. About 3 μm thick YBCO films grown on a single MOD–LZO buffered Ni–3W substrates using pulsed laser deposition show a critical current density, Jc, of 0.55 MA/cm2 (Ic of 169 A/cm) at 77 K and 0.01 T. This work holds promise for a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.

Bend strain tolerance of YBa2Cu3O7−x-coated conductors fabricated by inclined substrate deposition

The effect of tensile bend strain on the critical current ofYBa2Cu3O7−x (YBCO)-coated conductors was evaluated as a function of YBCO film thickness. TheYBCO-coated conductors were fabricated on Hastelloy C276 metal substrates templatedwith MgO by inclined substrate deposition. It was observed that a conductor with0.2 µm thick YBCO retained 90% of the unstrained critical current until a strain of≈0.4%, whereas for aconductor with 0.5 µm thick YBCO film the critical strain value was≈0.2%. At strains higher than the critical strain, the critical current dropped precipitously. Theinverse dependence of bend strain tolerance on the YBCO film thickness is in reasonableagreement with analytical prediction. This inverse dependence was used to approximate thefracture toughness of the YBCO film, which was found to be in general agreement with theliterature.

YBCO film growth on CeO2-buffered YSZ substrate by the full-solution method

The full-solution method has been developed as a low-cost process for makingYBa2Cu3O7−x (YBCO) coated conductors. In this study, highly biaxially texturedCeO2 buffer layers have been fabricated on yttria-stabilized zirconia (YSZ) single-crystalsubstrates by the sol–gel method using inorganic cerium nitrate as the starting precursormaterial. High-quality superconducting YBCO film has also been fabricated onCeO2-buffered YSZ substrate by the trifluoroacetate metal–organicdeposition (TFA-MOD) method. For YBCO superconducting film, only(00l) diffraction peaks can be detected by x-ray diffraction (XRD) analysis. Also from theXRD analysis, the YBCO films show sharp in-plane and out-of-plane texturefor all samples, which indicates that the YBCO film is epitaxially grown on theCeO2 buffer layer. From scanning electron microscope (SEM) observations, the YBCOfilm shows a uniform surface structure. A critical transition temperature,Tc 0, of 91 K and a critical current density of3 MA cm−2 (77 K, self-field)were obtained for a 0.2 µm thick YBCO film on CeO2-buffered YSZ substrate.

Rapid processing method for solution deposited YBa 2Cu 3O 7− δ thin films

YBa 2Cu 3O 7− δ (YBCO) films, deposited on buffered metal substrates, are the primary candidate for second-generation superconducting (SC) wires, with applications including expanded power grid transmission capability, compact motors, and enhanced sensitivity magnetic resonance imaging. Feasibility of manufacturing such superconducting wires is dependent on high processing speed, often a limitation of vapor and solution-based YBCO deposition processes. In this work, YBCO films were fabricated via a new diethanolamine-modified trifluoroacetic film solution deposition method. Modifying the copper chemistry of the YBCO precursor solution with diethanolamine enables a hundredfold decrease in the organic pyrolysis time required for MA/cm 2 current density ( J c) YBCO films, from multiple hours to ∼20 s in atmospheric pressure air. High quality, ∼0.2 μm thick YBCO films with J c (77 K) values ⩾2 MA/cm 2 at 77 K are routinely crystallized from these rapidly pyrolyzed films deposited on LaAlO 3. This process has also enabled J c (77 K)=1.1 MA/cm 2 YBCO films via 90 m/h dip-coating on Oak Ridge National Laboratory RABiTS™ textured metal tape substrates. This new YBCO solution deposition method suggests a route toward inexpensive and commercializable ∼$10/kA m solution deposited YBCO coated conductor wires.

Pulsed laser deposition of YBCO thin films on IBAD–YSZ substrates

High-quality YBa2Cu3O7−x (YBCO) films were fabricated on yttria-stabilized zirconia (YSZ)-buffered Hastelloy C276 substrates by pulsed laser deposition. YSZ was grown by ion-beam-assisted deposition. A thin (≈10 nm) CeO2 layer was deposited before the deposition of YBCO. The crystalline structure and biaxial texture of the YBCO film and the buffer layer were examined by x-ray diffraction 2θ-scan, ϕ-scan and pole-figure analysis. Epitaxial growth of the YBCO film on the buffer layer was observed. Full width at half maximum (FWHM) value of 7.4° was measured from the ϕ-scan of YBCO(103). Raman spectroscopy showed compositional uniformity and phase integrity in the YBCO films. Surface morphologies of the YBCO films were examined by scanning electron microscopy. Comparative studies indicated that the CeO2 buffer layer significantly improves the structural alignment and superconducting properties of YBCO films. Tc = 90 K, with sharp transition, and transport Jc = 2.2 × 106 A cm−2 at 77 K in zero-external field were obtained on the 0.5 μm thick YBCO films. The dependence of Jc on the FWHM of the YBCO(103) ϕ-scan indicated that high Jc is associated with low FWHM.

Angular dependence of critical current properties in YBCO coated tape under high magnetic field up to 18 T

Critical current properties in a YBCO coated tape have been studied as a function of temperature, magnetic field and field angle under high magnetic field up to 18 T. 1 μm thick YBCO film was deposited on a bi-axially aligned Y 2O 3/YSZ/Hastelloy substrate fabricated by the IBAD technique. The value of critical current, I c, of the 1 cm wide tape reached as high as 85 A at 77 K in self-field condition. After etching the tape into 100 μm wide and 1 mm long bridge, we measured extended E– J characteristics. The value of critical current density, J c, is maintained higher than 10 5 A/cm 2 at 70 K in 5 T perpendicular to the tape surface. Moreover, the power index n and the so called glass–liquid transition field, B GL, of the tape in perpendicular field are superior to those of epitaxial film deposited on a SrTiO 3 single crystalline substrate. J c vs. angle relationship shows broad peak around 90° where field is perpendicular to the tape surface, in addition to a sharp peak at 0°. These results suggest that the tape is highly uniform and correlated defects along c-axis direction contribute to flux pinning.

Continuous YBCO deposition by MOCVD for coated conductors

MOCVD is an economic method for the production of coated conductors. A single source MOCVD-system for continuous deposition on metal tapes was developed. Single crystals, IBAD buffered tapes and textured Ni-tapes were transported through the deposition zone and coated with YBCO. The velocity for the substrate transport was 4 m/h. On single crystals and IBAD buffered substrates the best critical current density of the 300–350 nm thick YBCO films were 2.5 and 4.8 MA cm −2 at 77 K. On CeO 2/YSZ/CeO 2 buffered textured nickel tapes the j c of the 500 μm thick YBCO film was 0.25 MA cm −2 at 77 K. Textured oxide buffer layers were deposited by MOCVD on single crystals and textured Ni in reducing atmosphere.

Recent progress in continuously processed IBAD MgO template meters for HTS applications

We discuss our recent progress using IBAD MgO as a template for subsequent deposition of YBa 2Cu 3O 7− δ (YBCO) high-temperature superconductors on metallic substrate tapes. We have refined the process by improving substrate preparation and by using reflected high-energy electron diffraction to monitor and improve IBAD MgO films. High quality, continuously processed IBAD MgO (c-IBAD) has been deposited on moving meter-length metal tape. By incorporating these optimized processing parameters, we have been able to deposit biaxially textured MgO on metallic substrates continuously with the best in-plane mosaic spreads near 9°. The subsequent pulsed laser deposition of 1–2 μm thick YBCO films on c-IBAD has resulted in superconducting transport critical current densities>1 MA/cm 2 (75 K, SF) on small area samples. Longer 4.5 cm samples of c-IBAD tape have also been coated with a 1 cm wide sample carrying 93 A (75 K, SF) for a 1.5 μm thick YBCO.

High-temperature superconducting thick films with enhanced supercurrent carrying capability

We have developed a multilayer architecture to enhance the supercurrent carrying capability of thick (>1 μm) YBa2Cu3O7−x (YBCO) films. An interlayer of CeO2, which functions as a starting template for growth of subsequent high-quality YBCO layers, is used to prohibit the generation of microstructural defects that otherwise develop in the top region of thick YBCO films. Improved surface quality for a 3.3 μm thick YBCO film has been confirmed by the channeling data of Rutherford backscattering spectroscopy and by scanning electron microscopy. Compared to our routinely prepared single-layer YBCO thick film in which the supercurrent drops rapidly with increasing film thickness, this multilayer makes it possible to maintain critical current density over 1 MA/cm2 with less restrictions on the thickness of coated conductors.

Progress towards a low-cost commercial coated conductor

ABSTRACTYBCO films prepared from metal trifluoroacetate (TFA) precursors on oxide-buffered textured non-magnetic substrates have achieved performance levels equaling that on oxide buffered textured Ni substrates. Critical current densities of 0.7 MA/cm2 to 1.0 MA/cm2 have been achieved in 0.4 µm thick YBCO films on short-length of CeO2/YSZ/Y2O3/Ni/Ni-13wt%Cr substrates. High-quality epitaxial buffers comprising a Ni layer, Y2O3 seed, YSZ barrier and CeO2 cap layers have been deposited over meter long tapes of deformation textured Ni and Ni-13%Cr using reel-to-reel processes. High-performance TFA-based YBCO films have been deposited on 0.1 m to 0.3 m lengths of these oxide buffered substrates using reel to reel processes. Critical current densities up to 1.0 MA/cm2 have been achieved in 0.4 µm thick YBCO films on CeO2/YSZ/Y2O3/Ni substrates. Using multiple coats of the metal trifluoroacetate precursors, thicker YBCO films have been demonstrated on oxide buffered substrates. Critical currents in excess of 100A/cm-width have been achieved for 1.2 µm -1.6 µm thick YBCO films on short lengths of CeO2/YSZ/Y2O3/Ni substrates.

Orientation transition in a thick laser deposited YBa 2Cu 3O 7− x film observed by glancing angle X-ray diffraction

Pulsed laser deposition (PLD) has been used to fabricate superconducting YBa 2Cu 3O 7− x (YBCO) films on MgO substrates. A Nd:YAG laser with a wavelength of 355 nm was used to grow 1 μm and 2 μm thick YBCO films. The relation of thickness and orientation in laser ablated films was systematically investigated by X-ray diffraction (XRD). The electrical property and the structural characteristics of YBCO films have been studied by R– T measurement and XRD. Glancing angle XRD pattern reveals the film orientation is changed from fully c-axis near the substrates/film interface to the mixture of a-axis and c-axis near the film surface. The intensity of the a-axis fraction is increased as going to near the film surface and as growing thicker films. We could get c-axis-oriented YBCO films by optimizing the film thickness and the deposition temperature.

Preparation of superconducting multilayer structure for power electronic devices

Multi-step KrF excimer pulsed laser deposition (MSPLD) technique has been developed to fabricate high-quality micrometer thick superconducting YBa 2Cu 3O 7−X (YBCO) films. As has been shown, a crystallization of YBCO at the initial stage of deposition crucially affects on thick YBCO film performance. Smooth, c-axis oriented 1- μm thick YBCO films with the critical temperature of T c(zero)=89.5 K and the overall critical current density of J c(77 K)=10 5 A/cm 2 have been prepared on the single crystal MgO substrate in three-step process by monitoring the laser fluence, laser repetition rate and substrate temperature. Micrometer thick YBCO films on the single crystal LaAlO 3 substrate show T c(zero)=85.7 K and J c(77 K)=10 3 A/cm 2, indicating that optimization of MSPLD processing conditions is much more critical for substrates with a small substrate/film lattice mismatch. Furthermore, Pb(Zr,Ti)O 3(PZT)/YBa 2Cu 3O 7−X/MgO heterostructures have been prepared by MSPLD technique with the critical temperature of T c(zero)=82.0 K in superconducting YBCO layer.

Surface smoothness of YBCO thin-films deposited by RF-sputtering

YBCO thin films were deposited on MgO by RF-sputtering. The effects of substrate position during the deposition, substrate temperature and annealing conditions on film characteristics such as surface smoothness, crystallinity and electrical properties were investigated. The results of Talystep measurement showed that a smoothness of 5 nm with 0.4 μm-thick YBCO film was obtained when the substrate was placed normal and around the sputtering target. The surface smoothness was affected not only by deposition condition but also by post-annealing. The suitable annealing condition was 900 °C for 60 min. A zero-resistance temperature as high as 85 K was obtained reproducibly and this value did not change over 150 days.