YBa2Cu3O7-x Research Articles

Averaged effective pinning potential in YBCO single crystals nearTc

In this paper we present our results on the low density magnetic flux pinning characteristics, obtained though HTSC samples magnetization relaxation measurements M(t) near the phase transition temperatures (0,8 < T/Tc > 0,99).As the main object of investigation we have chosen pure YBa2Cu3O7-x (YBCO) single crystal samples with optimal oxygen saturation. We note the presence of strong pinning in the system of unidirectional planar defects and a significant nonmonotonicity of the Up(T) dependence behavior for low density trapped magnetic flux.

Irradiation Response of Next Generation High Temperature Superconductors for Fusion Energy Applications

The latest generations of rare-earth substituted and nano-doped YBa2Cu3O7-x (YBCO) high temperature superconductors (HTS) developed for applications in magnetic fields are being evaluated for potential use in fusion energy applications. The benefits include increased plasma performance and reduced system cost through more compact and cryoplant-free fusion energy systems. The response to ion irradiation of commercially produced GdBa2Cu3O7-x, (Y,Dy)Ba2Cu3O7-x, and Zr-doped (Y,Gd)Ba2Cu3O7-x samples was investigated. These state-of-the-art conductors represent different design methods for enhanced flux pinning, resulting in different responses to radiation damage. Irradiations using 5-MeV Ni and 25-MeV Au ions were used to examine cascade damage while keeping electronic energy loss levels below columnar defect thresholds. An improved radiation tolerance is found in these new generation HTS conductors. Specifically, the influences of irradiation on the superconducting critical temperatures and the electrical transport properties of the samples were much less than that observed on the earlier generation of irradiated HTS materials investigated by others.

The abnormal temperature-dependent rectification effect in BiFeO3/YBa2Cu3Ox heterostructures

We report the fabrication and properties of heterostructures formed by the BiFeO3 (BFO) ferroelectric and YBa2Cu3Ox (YBCO) superconductor. Four measurement configurations on BFO/YBCO heterojunctions are proposed and showed different I-V characteristics. Moreover, one type of BFO/YBCO heterostructures which had the strongest rectification effect at 15K, showed the abnormal rectification effect dependent on temperature. The rectifying effect enhanced with decreasing temperature below the superconducting transition temperature of YBCO. YBCO electrode played an important role in increasing the rectifying parameter because of the high density of states for quasi-particles in YBCO in the superconducting state.

Superconducting properties of experimental YBCO coils for FFAG accelerator magnets

A project to develop fundamental technologies for accelerator magnets using high-Tc coated conductors is currently in progress. The primary applications of this project are fixed field alternating gradient (FFAG) accelerators for carbon cancer therapy systems and accelerator-driven subcritical reactors. Several types of superconducting coils for FFAG accelerators have been conceptually designed. These coils have complicated shapes, including a negative-bend part or a three-dimensional bent part. One of the aims of the project is to establish winding technologies for complicated coil shapes using coated conductors. To demonstrate winding technologies for YBa2Cu3O7-x (YBCO) coils, small test coils having a negative-bend part or a three-dimensional bent part were designed and fabricated according to the present design of the FFAG magnet. The outside dimensions of the negative-bend test coil were 460 mm long and 190 mm wide, and the radius of curvature of the negative-bend part was 442 mm. The outside dimensions of the three-dimensional test coil were 380 mm long and 280 mm wide, and the radius of curvature of the mandrel of the three-dimensional coil was 700 mm. The test coils were wound using YBCO coated conductors with a length of about 100 m and were then impregnated with epoxy resin. The coils were placed in liquid nitrogen and excited to measure their V-I characteristics. From the V-I characteristics throughout a voltage range down to 10−9 V/cm, the V-I characteristics before and after impregnation were approximately the same, demonstrating that the superconducting properties were not degraded.

Nonuniform magnetic stresses in high temperature superconducting thin films

We provide an experimental measurement of the magnetic stresses in high temperature superconducting thin films based on the Coherent Gradient Sensor which has many merits such as real time, non-destructive, full field, vibration insensitivity, etc. As an example, the radial stress, hoop stress of the YBa2Cu3O7-x (YBCO) film, and shear stress between the film and the (00l) SrTiO3 substrate subjected to various magnetic fields at 40 K are obtained. For the interfacial shear stress in radial direction between the film and substrate, it is found that the magnitude order of which is at GPa at somewhere under a small magnetic field.

The Effect of Polyethyleneimine (PEI) on the Texture and Morphology of YBCO Films

The effect of polyethyleneimine (PEI) in precursor solution on the morphology and superconducting properties of YBa2Cu3O7-x (YBCO) films grown on LaAlO3 (LAO) substrates by metal-organic deposition (MOD) method was investigated. The morphologies of the YBCO films were different based on the different amount of PEI addition from 0.25 g to 0.9 g in 10 mL precursor solution. Furthermore, research results indicate that the PEI helps to improve the critical current density (Jc), the uniformity of surface morphology and c-axis orientation of thin film. The highest critical current density (Jc) of 2.17 MA/cm2 at 77 K is obtained in YBCO films fabricated on LAO substrates when the amount of PEI is 0.5 g in 10 mL precursor solution. YBCO layers with about 400 nm in thickness can be processed without cracks and holes during the whole heat treatment, which takes only 7.5 h.

Enhanced Quench Propagation in $Bi_{2}Sr_{2}CaCu_{2}O_{x}$ and $YBa_{2}Cu_{3}O_{7-x}$ Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator

The significant amount of energy stored in a large high-field superconducting magnet can be sufficient to destroy the coil in the event of an unprotected quench. For magnets based on high-temperature superconductors (HTSs), such as Bi2Sr2CaCu2Ox (Bi2212) and YBa2Cu3O7-x (YBCO), quench protection is particularly challenging due to slow normal zone propagation. A previous computational study showed that the quench behavior of HTS magnets is significantly improved if the turn-to-turn electrical insulation is thermally conducting, enhancing 3-D normal zone propagation. Here, a new doped-titania electrical insulation with high thermal conductivity is evaluated. The thermal conductivity of the insulation is measured at cryogenic temperatures, and its chemical compatibility with Bi2212 round wires is determined. Thin layers of the insulation are deposited onto the surface of Bi2212 and YBCO wires, which are then wound into small coils to study the quench behavior. Results show that the critical current and homogeneity of Bi2212 coils are improved relative to coils reacted with mullite insulation. Relative to similar coils with conventional insulation (mullite for Bi2212 and Kapton for YBCO), the turn-to-turn quench propagation is increased by a factor of 2.8 in Bi2212 coils at 4.2 K and self-field and by a factor of 2.5 in YBCO coils at 4.2 K and 5 T. These results indicate that doped-titania insulation may significantly improve Bi2212 and YBCO coils. Increased normal zone propagation velocity enhances quench detection and quench protection, and the thinness of the insulation relative to the most common alternatives increases the magnet winding pack current density and reduces the coil specific heat.

A 7–8.5 GHz High Performance MMIC HTS Josephson Mixer

A low-loss, low power consumption monolithic high-temperature superconducting (HTS) Josephson junction mixer at 7-8.5 GHz is presented. The mixer consists of a HTS YBa2Cu3O7-x (YBCO) bandpass filter for RF input, a lowpass filter for IF output and a LO resonator integrated with a single Josephson junction. All the passive and active devices are fabricated on a 20 mm×10 mm MgO substrate. Measurement result shows a conversion gain of -7 dB at 40 K, and -4.7 dB at 20 K. The IF output versus the RF input exhibits a wide linear range of conversion gains. The mixer has an extremely low LO power requirement at -32 dBm and a 50 nW power consumption.

MOD Derived Pyrochlore Films as Buffer Layer for All-Chemical YBCO Coated Conductors

We report a detailed study performed on La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> pyrochlore material grown by the metal-organic decomposition method as buffer layers for 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-x</sub> (YBCO) coated conductors. High-quality epitaxial LZO thin films have been obtained on single crystal (SC) and Ni-5 %at.W substrates. In order to evaluate structural and morphological properties, films have been characterized by means of X-ray diffraction analyses, atomic force microscopy, and scanning electron microscopy. Precursor solutions and heat treatments have been studied by thermogravimetric analyses and infrared spectra with the aim of optimizing the annealing process. Thin films of YBCO have been deposited by pulsed laser ablation on this buffer layer. The best results obtained on SC showed YBCO films with critical temperature values above 90 K, high self-field critical current density values (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> >; 1 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and high irreversibility field values (8.3 T) at 77 K together with a rather high depinning frequency ν <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> (0.5 T, 77 K) >; 44 GHz as determined at microwaves. The best results on Ni-5% at.W has been obtained introducing in the heat treatment a pyrolysis process at low temperature in air in order to remove the residual organic part of the precursor solution.

Two-layer batch-process of YBa2Cu3Ox bulk superconductors induced by NdBa2Cu3Ox film-seeds

Applying a cost-effective process with a simple one-side-heating furnace, two layers of YBa2Cu3Ox (YBCO) bulks were successfully grown in one batch by using NdBa2Cu3Ox (NdBCO) thin-film-seeds deposited on MgO substrates. Due to the large temperature difference between the two layers, the seed-induced growth began at the bottom layer much later than that at the top layer. Remarkably, NdBCO films on the bottom layer samples survived a long time (over 15 h) above the growth temperature and effectively induced the YBCO growth. The significant thermal stability of the films, i.e., the tolerance for a long holding time on the surface of the molten pellet, is supposed to relate to a competition between the dissolution/diffusion of film materials into the liquid and NdBCO grain coarsening/Nd-YBCO crystallization.

Low-noise single-layer YBa2Cu3O7-x dc superconducting quantum interference devices magnetometers based on step-edge junctions

We report the performance of twenty-four high temperature superconducting dc superconducting quantum interference devices (SQUIDs) whose Josephson junctions were formed from a YBa2Cu3O7-x (YBCO) grain boundary on an engineered MgO step-edge substrate. Each device has the same SQUID design with an inductance of 65 pH, and consisted of two SQUIDs with different junction widths, connected in series, and directly coupled to a large pick-up loop of 7.5 mm × 8.8 mm on a 1 × 1 cm2 chip. 58% of the devices had a peak-to-peak modulation voltage, ΔV, larger than 30 μV. The typical values of the white flux and field noise were 4.7 μΦo and 56 fT/Hz, respectively, in a magnetically shielded environment with 1/f corner frequency at 15–20 Hz. In an unshielded environment, there was no degradation of white noise.

Electrospinning preparation and high-temperature superconductivity of YBa2Cu3O7-x nanotubes

YBa2Cu3O7-x (YBCO) nanotubes (NTs) with high-temperature superconductivity (HTS) were successfully synthesized by electrospinning. A solution of PVP and Y–Ba–Cu acetates was used as precursor in the electrospinning to get nanofibers (NFs). Considering the necessary conditions for NTs formation, a well-designed thermal treatment procedure was carried out to turn the as-spun NFs into NTs. The hollow structure and stoichiometric ratio of the YBCO NTs were validated through TEM and EDX analysis. Due to comparative characterizations of superconductivity between YBCO NTs and bulk sample, it can be concluded that YBCO NTs has HTS but with broader transition temperature width and higher resistance above onset temperature. These novel features were induced by phase slip mechanism and unique structure. This work provides a simple and efficient route to obtain YBCO NTs, which may have new transition properties and significant applications in further researches.

Effect of Firing Temperature on Microstructure and Superconductivity of YBCO Films Derived from Low-Fluorine Solution

Using a low-fluorine solution, YBa2Cu3O7-x (YBCO) superconducting films were prepared on LaAlO3 (LAO) substrates by dip-coating method. YBCO films were fired at different temperatures with same oxygen pressure of 1.3 vol% and water vapor pressure of 7.4 vol%. Effect of firing temperature on film microstructure and superconductivity was investigated. The results indicated that YBCO films with high-degree c-axis orientation (the degree of c-axis orientation reached 96%) can be obtained when heat treated at 800 °C. At this temperature YBCO films were grown on LAO with cubic-on-cubic mode, resulting in a high critical transition temperature (Tc) of 91.5 K, and critical current density (Jc) of lager than 1 MA/cm2. However, when fired at lower temperatures, YBCO films trended to form a-axis grains, which degraded Jc of films. And a higher heat treatment temperature also depressed superconductivityof YBCO films.

Laser Direct-Write for Low AC Loss High Temperature Superconductor Applications

The use of high temperature superconductors (HTS) in applications such as power cables, fault current limiters, and electromagnets, has seen rapid growth in recent years. While HTS exhibit zero dc resistance, appreciable ac losses are observed when the HTS are subject to an applied ac magnetic field. By dividing the HTS films into thin filament arrays and creating periodic metallic cross-overs to allow for flux penetration, the ac loss of the HTS can be significantly reduced. The HTS, YBa2Cu3O7-x (YBCO), films were prepared from the metal organic decomposition of a trifluoroacetate-based (TFA) precursor solution onto buffered substrates, manufactured by AMSC. To deposit the TFA solutions onto the buffered substrates, a new laser direct-write (LDW) technique was developed. LDW is a non-contact, non-lithographic process that relies on the mask-less printing of functional materials, such as metallic inks. The transferred TFA precursor filaments were then decomposed and subsequently characterized. In addition to the deposition of TFA precursors onto buffered substrates, LDW was used to print silver lines for metallic crossovers onto HTS tapes. These results show LDW to be a promising technique for the fabrication and modification of high temperature superconductors.

Substrate decoration for improvement of current-carrying capabilities of YBa2Cu3Ox thin films

The effects of substrate decoration with yttria and Y:ZrO2 on the structural and electrical properties of the YBa2Cu3Ox (YBCO) thin films are studied. The films were deposited on (LaAlO3)3–(Sr2AlTaO8)7 substrates by pulsed laser deposition. Two different structures of decoration layer were applied, a template layer of nanoparticles and an uniform ultra-thin layer. Significant improvement of current-carrying capabilities was observed, especially at high external magnetic fields. Structural studies of these films reveal the presence of extended linear defects in the YBCO matrix. The formation of these structures is attributed to seeding of randomly oriented YBCO grains due to suppression of epitaxy in the very beginning of the deposition. The films of both kinds of decoration layers show nearly the same improvement of jC over the reference film at 77 and 50K: jC (5T and 50K) reaches 0.92 and 0.97MA/cm2 for uniform and template decoration layers. At 5 and 20K the effect of template decoration layers is more beneficial: jC (5T and 20K) values are 3.5 and 4.1MA/cm2, jC (5T and 5K) values are 6.4 and 7.9MA/cm2, for uniform and template decoration layers, respectively.

Experimental Design and Investigation of Novel Pulsed Laser Deposited Structures for YBCO Based Coated Conductors

ABSTRACTThe study of high quality YBa2Cu3O7-x (YBCO) based superconducting films is a fundamental issue to be addressed when dealing with the realization of efficient coated conductors with large current carrying capacity. In this perspective the investigation of innovative buffer layers structures able to allow epitaxial YBCO film grow on metallic substrates and to prevent contamination and degradation issues holds a central role.In this work we thoroughly study the properties of YBCO films grown by means of pulsed lasers deposition on CeO2 template on both bare MgO single crystal and MgO-homoepitaxial/MgO single crystal substrates. Due to its high chemical and temperature stability the MgO reduces the oxygen diffusion effects. On the other hand, the CeO2 layer, pulsed laser deposited, prevents the YBCO film from metallic contamination and facilitates its epitaxial growth. Morphology and crystalline structure of buffer layers and superconductors film are investigated by using scanning electron microscopy (SEM), X-ray and electrons back-scattered diffraction techniques (XRD and EBSD).YBCO films show good critical temperature values (Tc &gt; 87K) with sharp transitions. These encouraging results make our structures promising candidates in the realization of high quality YBCO based coated conductors.

MOD oxide buffer layers on metallic substrates for YBCO coated conductors

ABSTRACTWe present a detailed study carried out on oxide buffer layers grown by Metal-Organic Decomposition (MOD) on metallic substrates for YBa2Cu3O7-x (YBCO) coated conductor applications. Precursor solutions have been made starting from acetates or pentanedionates and characterized by means of Differential Scanning Calorimetry (DSC) and Thermogravimetric (TG) analyses coupled with Fourier Transform Infra-Red spectroscopy (FT-IR). Thin buffer layers have been grown by spin-coating on Ni-5at.%W substrates. X-ray diffraction spectra (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) have been employed in order to optimize buffer layers in terms of film microstructure and surface quality, with the final aims of producing a suitable template for YBCO growth. It will be shown that the optimization of the recrystallization process can lead to high quality buffer layer allowing the growth of YBCO films showing good superconductive properties.

Enhanced flux pinning in MOD-YBCO films with co-doping of BaCeO3 and Y2O3 nanoparitcles

Enhancing the critical-current density of YBCO films is essential to gain a deeper understanding of the vortex pinning mechanisms and enable commercial applications of high-temperature superconductivity. Combined BaCeO3 and Y2O3 nanoparticles have been achieved to be co-doped in YBa2Cu3O7-x (YBCO) films by metalorganic deposition using trifluoroacetates (TFA-MOD). The formation of integrated nanoparticles increases the critical current density (Jc) of Y2O3/BaCeO3 doped-YBCO films while keeping the critical transition temperature (Tc) close to that in the pure YBCO films. YBCO film containing BaCeO3 and Y2O3 showed Tc value of 91 K and Jc value of 5 MA/cm2 at self-field (0 T, 77 K). The strongly enhanced flux pinning over a wide range of magnetic field may be attributed to the combined BaCeO3 and Y2O3 created by optimized TFA-MOD conditions.

PULSED LASER DEPOSITION — ABLATION MECHANISM AND APPLICATIONS

Laser ablation is the process of removing material from a solid surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave laser beam if the laser intensity is high enough. In general, the method of pulsed laser deposition (PLD) is simple. Only few parameters need to be controlled during the process. Targets used in PLD are small compared with other targets used in other sputtering techniques. It is quite easy to produce multi-layer film composed of two or more materials. Besides, by controlling the number of pulses, a fine control of film thickness can be achieved. Pulsed-laser deposition has been used to deposit an extraordinarily wide range of materials. Historically, the most significant application of PLD has been in the area of high temperature superconducting thin films. The demonstration that PLD could be used to deposit YBa2Cu3O7-x (YBCO) films with zero resistivity at nearly 85 K sparked a significant amount of high temperature superconductivity research over the past decade and has stimulated research in PLD in general. The most striking limitations of PLD are the generation of particulates during the deposition process and the non uniform coating thickness, when substrates of large area are deposited.

AC Losses of Copper Stabilized Multifilament YBCO Coated Conductors

We report the data on magnetization losses and critical current of multifilament copper stabilized coated conductors. Eight centimeters long samples of copper stabilized YBa2Cu3O7-x (YBCO) coated conductors manufactured commercially were subdivided into superconducting filaments by near-IR laser micromachining. The width of the superconducting stripes was varied from 0.2 mm to 0.04 mm. Some of the samples were striated leaving superconducting bridges for current sharing between the filaments. The AC losses were measured at different sweep rates of the magnetic field up to 14 T/s. We will present the results for the hysteresis and coupling losses and discuss the means to reduce the coupling loss by changing the processing parameters of micromachining and by post-ablation treatment.