YBCO Superconductors Research Articles

Effect of Premagnetization on Self-Stable Force Characteristics in a Space Superconducting Interface Structure

Under the condition of field-cooling magnetization, the superconductor can trap magnetic flux and form a self-stabilizing state within it because of the flux-pinning effect. In most cases, the superconductor interacts with a magnet that is also used to magnetize the superconductor, and then, some self-stabilizing structure such as the magnet-superconductor suspension is achieved for application. However, in some actual applications, such as the space superconducting interface, the superconductor has to be magnetized by some background magnets and then interacts with other magnets, which is called premagnetization; hence, the self-stability between the magnetized superconductor and the interacting magnet should be different. To investigate self-stabilizing properties after premagnetization, an experiment is designed to study quasi-static force characteristics between a permanent magnet and an YBCO superconductor magnetized by a superconducting coil. Through comparing the experimental results in different premagnetization conditions, we found that the force characteristics in these conditions are obviously different because of the difference of the magnetic field distribution in the magnetized superconductor. These force properties can be affected by changing the magnetization current and the position of the superconducting coil. With reasonable adjustments, the on-site premagnetization can realize strong self-stabilizing characteristics for the space interface.

Quantitative nanoscale vortex imaging using a cryogenic quantum magnetometer.

Microscopic studies of superconductors and their vortices play a pivotal role in understanding the mechanisms underlying superconductivity. Local measurements of penetration depths or magnetic stray fields enable access to fundamental aspects such as nanoscale variations in superfluid densities or the order parameter symmetry of superconductors. However, experimental tools that offer quantitative, nanoscale magnetometry and operate over large ranges of temperature and magnetic fields are still lacking. Here, we demonstrate the first operation of a cryogenic scanning quantum sensor in the form of a single nitrogen-vacancy electronic spin in diamond, which is capable of overcoming these existing limitations. To demonstrate the power of our approach, we perform quantitative, nanoscale magnetic imaging of Pearl vortices in the cuprate superconductor YBa2Cu3O7-δ. With a sensor-to-sample distance of ∼10 nm, we observe striking deviations from the prevalent monopole approximation in our vortex stray-field images, and find excellent quantitative agreement with Pearl's analytic model. Our experiments provide a non-invasive and unambiguous determination of the system's local penetration depth and are readily extended to higher temperatures and magnetic fields. These results demonstrate the potential of quantitative quantum sensors in benchmarking microscopic models of complex electronic systems and open the door for further exploration of strongly correlated electron physics using scanning nitrogen-vacancy magnetometry.

Improvement of MTG Process for Preparation and its property of YBCO Superconductor

<p>To improve the superconductivity of high temperature YBCO superconductor, it was prepared and examined by MTG (melt-textured growth) process with use of SmBaCuO seed crystal for orientation, additives of Ag and 211 phase for current density and flux pinning, and heat treatment for oxygen absorption. SmBaCuO single crystals were prepared by MTG process with oxygen absorption and analyzed by XRD and Laue technique. It was estimated that optimum value of Y<sub>2</sub>BaCuO<sub>5</sub> (211 phase) contents in the textured YBCO superconductor as flux pinning center was about 20 wt.%. Ag contents have no influence on the critical temperature but have large influence on the critical current density of the textured YBCO. In the YBCO matrix in experiment, 10 wt.% of Y<sub>2</sub>BaCuO<sub>5</sub> was added, the final 211 content of YBCO made by MTG process could reach about 20 wt.% which was the optimum value for the critical current density. The Ag contents in textured YBCO and the effects of Ag on the superconductivity were also examined. A 5x5x2 mm<sup>3</sup> single crystal of SmBaCuO grown by the melted-condensed process was used to be the seed crystal in the preparation of YBCO. It was proved that the orientation of YBCO was the same as the orientation of the SmBaCuO seed. The effect of oxygen absorption of the bulk oriented YBCO was studied and the heat treatment of oxygen absorption would be in flowing oxygen, at 400 for about 24 hours. The critical current density of the textured YBCO prepared by the optimum technical conditions was about 7x10<sup>4</sup> A/cm<sup>2</sup> (77K, 0.01T).</p>

Moist Corrosion and Surface Protection of YBCO Superconductors

<p>The critical currents of sintered YBa<sub>2</sub>Cu<sub>3</sub>O<sub>6.5+</sub><sub>δ</sub>were measured as the variables with the corrosive time in the humid air. The corrosive process was studied by means of the current changes. Ag coating on the textured YBCO and polytetrafluoroethylene (PTFE) coating on the sintered YBCO were prepared. The critical current densities of different YBCO samples with and without coatings were compared. Both Ag coating and PTFE coating can well protect YBCO from moisture and CO<sub>2</sub>.</p>

A fully superconducting bearing system for flywheel applications

A fully superconducting magnetic suspension structure has been designed and constructed for the purpose of superconducting bearing applications in flywheel energy storage systems. A thrust type bearing and two journal type bearings, those that are composed of melt textured high-Tc superconductor YBCO bulks and Nd-Fe-B permanent magnets, are used in the bearing system. The rotor dynamical behaviors, including critical speeds and rotational loss, are studied. Driven by a variable-frequency three-phase induction motor, the rotor shaft attached with a 25 kg flywheel disc can be speeded up to 15 000 rpm without serious resonance occurring. Although the flywheel system runs stably in the supercritical speeds region, very obvious rotational loss is unavoidable. The loss mechanism has been discussed in terms of eddy current loss and hysteresis loss.

Superconductor Joule Losses in the Zero-Field-Cooled Maglev Vehicle

This paper estimates for the first time the Joule losses in the YBCO superconductors in the zero-field-cooled (ZFC) Maglev vehicle. Imposing a pendulum-like movement to the vehicle and since the aerodynamic losses were taken into account in the experiments, obtained results show that the Joule losses occurred in the superconductors during the vehicle's movement. Four movement tests were completed, which allow measuring the average losses in superconductors that were responsible by vehicle's damping. A finite-element model of the vehicle showed how and why YBCO Joule losses are function of the vehicle speed. It quantifies the losses and indicates that, in the ZFC-Maglev, these are clearly reduced since the significant losses are located only in a very small layer at the superconductors' surface.

Measurements and Numerical Simulations of Trapped Field in a Stack of HTS Tapes

Trapped field magnets are usually constructed on the base of bulk YBCO superconductors. However, recent achievements in the production of long-size coated conductors have opened the opportunity of using a tape stack for these applications. Better thermal conductivity, mechanical stability in high fields, and high critical current densities make such systems favorable. Moreover, the tape form of the conductor allows for organizing different spatial structures and optimizing device design. Trapped field was measured on the stack of high-temperature superconducting tapes in this work. An industrially stabilized (with copper shield) tape, which was produced by SuperOx company with GdBa 2 Cu 3 O 7-x superconductor inside, was used in experiments. The stack was made of 12-mm-diameter disk-shaped tapes, and the height was 20 layers. Magnetization was carried out by an 8-T superconducting magnet on the temperature of 77 K. To calculate the trapped field of a stack, field dependence and angular field dependence of critical current were measured on these tapes. The finite-element method was used for numerical simulations. It is shown that taking into account the magnetic field orientation in different areas of the stack leads to better agreement with the experimental measured trapped field values.

The influence of magnetic nano metal oxides doping on structure and electrical properties of YBCO superconductor

Superconductor samples of YBa2Cu3O7−δ (YBCO) + x where x = 0.1, 0.2, 0.3, 0.4 and 0.5 wt% of nano metal oxides namely Cr2O3, Co3O4 and Mn3O4 namely are synthesized by the solid-state reaction route. Both x-ray diffraction and electron microscopy have been employed to study the phase identification and the microstructure of these samples. Transition temperature of the samples has been determined by four probe resistivity measurements. The x-ray diffraction patterns indicate that the gross structure of YBCO does not change with the substitution of three types of nano metal oxides with different doping level. The critical transition temperature (Tc) is found to decrease with the increases of doping level. Mn3O4 has highest Tc value which may be due to flux pinning from some defects and the rapid suppression in Tc with increasing concentration of Mn3O4 may be due to the cooper pair breaking and the hole filling in the CuO2 planes.

Interfacial effects revealed by ultrafast relaxation dynamics inBiFeO3/YBa2Cu3O7bilayers

The temperature dependence of the relaxation dynamics in the bilayer thin film heterostructure composed of multiferroic BiFeO$_{3}$ (BFO) and superconducting YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) grown on a (001) SrTiO$_{3}$ substrate is studied by a time-resolved pump-probe technique, and compared with that of pure YBCO thin film grown under the same growth conditions. The superconductivity of YBCO is found to be retained in the heterostructure. We observe a speeding up of the YBCO recombination dynamics in the superconducting state of the heterostructure, and attribute it to the presence of weak ferromagnetism at the BFO/YBCO interface as observed in magnetization data. An extension of the Rothwarf-Taylor model is used to fit the ultrafast dynamics of BFO/YBCO, that models an increased quasiparticle occupation of the ferromagnetic interfacial layer in the superconducting state of YBCO.

Control of Y-211 content in bulk YBCO superconductors fabricated by a buffer-aided, top seeded infiltration and growth melt process

Bulk (RE)–Ba–Cu–O ((RE)BCO, where RE stands for rare-earth), single grain superconductors can trap magnetic fields of several tesla at low temperatures and therefore can function potentially as high field magnets. Although top seeded melt growth (TSMG) is an established process for fabricating relatively high quality single grains of (RE)BCO for high field applications, this technique suffers from inherent problems such as sample shrinkage, a large intrinsic porosity and the presence of (RE)2BaCuO5 (RE-211)-free regions in the single grain microstructure. Seeded infiltration and growth (SIG), therefore, has emerged as a practical alternative to TSMG that overcomes many of these problems. Until now, however, the superconducting properties of bulk materials processed by SIG have been inferior to those fabricated using the TSMG technique. In this study, we identify that the inferior properties of SIG processed bulk superconductors are related to the presence of a relatively large Y-211 content (∼41.8%) in the single grain microstructure. Controlling the RE-211 content in SIG bulk samples is particularly challenging because it is difficult to regulate the entry of the liquid phase into the solid RE-211 preform during the infiltration process. In an attempt to solve this issue, we have investigated the effect of careful control of both the infiltration temperature and the quantity of liquid phase powder present in the sample preforms prior to processing. We conclude that careful control of the infiltration temperature is the most promising of these two process variables. Using this knowledge, we have fabricated successfully a YBCO bulk single grain using the SIG process of diameter 25 mm that exhibits a trapped field of 0.69 T at 77 K, which is the largest value reported to date for a sample fabricated by the SIG technique.

Fabrication of Superconducting YBCO Nanoparticles by Electrospinning

High temperature superconductor YBa2Cu3O7-δ (HTS YBCO) nanoparticle was successfully prepared by electrospinning and sol-gel techniques. The sol-gel containing a homogeneous solutions of the precursor of Y-Ba-Cu acetate and Poly (vinyl pyrrolidone) PVP. The critical transition temperature (Tc) of the samples have been found using four point probe technique. By optimizing electrospinning, sol-gel process and heat treatment procedure, YBCO nanoparticle with a transition temperature of 78K was obtained. The surface area measurements of YBCO samples showed, high surface area 2.0 m2/g for nanoparticle, in comparison with block sample 1.0 m2/g. The structural Characterizations of YBCO samples demonstrated that, the YBCO nanoparticles have single phase orthorhombic structure which typical crowd nanoparticles diameter were 388nm. The Individual nanoparticle diameter were found between 20 and 50nm. The calcination temperature at 950 oC does not affect to decrease the surface area of YBCO samples. Electrospinning in combination with a sol-gel techniques are an effective routes to realize different nanostructure morphologies of YBCO superconductor. Production of HTS YBCO nanoparticle by these process promising practical applications.

Cation-stoichiometry of functional oxides modified by oxygen vacancy through growth kinetics control

Among all functional perovskite oxides, LRE-Ba-Cu-O (LREBCO, LRE123, LRE: light rare earth = Sm, Nd, et al.) superconductors possess outstanding properties of higher critical transition temperature (Tc) and higher critical current density (Jc) than YBCO superconductors. However, cation off-stoichiometry caused by the substitution of LRE elements for Ba sites could deteriorate superconducting properties. Here, we develop a new approach for fabricating high performance superconductors crystal of nearly ideal stoichiometric Sm1+xBa2-xCu3Oy (i.e. low x value) in air through oxygen vacancy control. In the peritectic reaction of Sm211 (solid) + Ba–Cu–O (liquid) + O2 (gas) → Sm1+xBa2-xCu3Oy (solid), the higher growth rate (achieved via the high cooling rate during growth) leads to the less absorbed-oxygen in Sm1+xBa2-xCu3Oy (i. e. low y value), which could balance the whole valence of cations to gain a low x value, equivalent to a low substitution level of Sm3+/Ba2+. As a result, by using the normal precursor (Sm123 + Sm211), SmBCO bulks with the high performance (Tcmid over 94 K with the sharp transition) are successfully grown in air. Thus this path effectively realizes the control of cation stoichiometry for SmBCO by oxygen vacancy modification, which could be applicable in synthesizing other functional oxides with desirable performance.

Effect of magnetic and nonmagnetic nano metal oxides doping on the critical temperature of a YBCO superconductor

Bulk superconductor samples of YBa2Cu3O7−δ (YBCO) doped with nano metal oxides of Mn3O4, Co3O4, Cr2O3, CuO and SnO2 respectively with 0.2 wt% are synthesized by a solid-state reaction route. The structural characterization of all samples has been carried out by x-ray diffraction (XRD) and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The XRD patterns indicate that the magnetic doping of nano metal oxides gives a high value of orthorhombicity of the YBCO samples which is the result of high oxygen content, and consequently could give better superconducting properties contrary to the non magnetic nano oxides (CuO, SnO2). The critical temperature (Tc) of the studied samples was found to improve by nano magnetic doping and lower with nano nonmagnetic doping. The superconducting transition temperature Tc determined from electrical resistivity measurements was found to increase for Mn3O4 (5.27 μB) doping and decrease for other metal oxides doping.

The effects of magnetization process on levitation characteristics of a superconducting bulk magnet

In this paper, a bulk YBCO superconductor was magnetized in a chosen magnetic field generated from a superconducting magnet (SM) after field cooling process. The effects of magnetization process with different magnetization intensities on levitation forces and relaxation characteristics were investigated. From the results, it can be confirmed that the superconducting bulk magnet (SBM) magnetized with proper magnetization intensity was beneficial to improve the levitation characteristics of the magnetic levitation system. Nevertheless, when the magnetization intensity exceeded 0.85T, the levitation forces and the relaxation characteristics of the SBM attained saturation.

Levitation forces of a bulk YBCO superconductor in gradient varying magnetic fields

The levitation forces of a bulk YBCO superconductor in gradient varying high and low magnetic fields generated from a superconducting magnet were investigated. The magnetic field intensity of the superconducting magnet was measured when the exciting current was 90 A. The magnetic field gradient and magnetic force field were both calculated. The YBCO bulk was cooled by liquid nitrogen in field-cooling (FC) and zero-field-cooling (ZFC) condition. The results showed that the levitation forces increased with increasing the magnetic field intensity. Moreover, the levitation forces were more dependent on magnetic field gradient and magnetic force field than magnetic field intensity.

Role of lattice in YBCO superconductors studied by Raman spectroscopy

In this paper, we systematically studied Ca–YBCO [Formula: see text] and CaLa–YBCO [Formula: see text] systems by Raman spectroscopy. It is found that [Formula: see text] is closely related to the vibration of lattice. In the Ca–YBCO system, the phonons around 115 and 335 cm[Formula: see text] harden as the [Formula: see text] decreases. Oppositely, the 140 cm[Formula: see text] mode and the 220 cm[Formula: see text] mode soften. In the CaLa–YBCO system, the [Formula: see text] decreases gradually with the content of Ca and La. The Raman peak of 140 cm[Formula: see text] mode hardens and the 360 cm[Formula: see text] mode softens. Besides, the fluctuations of phonons of 210 cm[Formula: see text] mode and 575 cm[Formula: see text] mode were observed.

The Nernst effect in ferromagnet–superconductor bilayer heterostructures

We report the transport properties of the La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7+d (YBCO) heterostructures in the vicinity of the superconducting transition. The bottom deposited manganite was an LSMO ferromagnet with a Curie temperature of 350 K, while the top deposited cuprate was a nearly optimally doped YBCO superconductor with Tc ∼ 90 K. The samples used in these studies had fixed a thickness of LSMO layer (90 nm), whereas the thickness of the YBCO layer was varied between 20 and 100 nm. Single YBCO layers with respective thicknesses were also measured for comparison. The mixed state properties of the bilayers and single layers were characterized by means of the Nernst effect and electrical resistance measurements in magnetic fields of up to B = 12.5 T. All investigated samples show a zero-resistance state below T = 60 K in a field of 12.5 T and demonstrate gradual degradation of the superconducting properties with decreasing thickness of the YBCO layer in bilayer structures.

A magneto-mechanical fully coupled model for giant magnetostriction in high temperature superconductor

This paper presents a fully coupled model to account for the flux pinning induced giant magnetostriction in type-II superconductors under alternating magnetic field The superconductor E-J constitutive law is characterized by power law where the critical current density is assumed to depend exponentially on the flux density. The governing equations of the two-field problem (i.e., the interactions of elastic and magnetic effects) are formulated in a two-dimensional model. The magnetostriction curves and magnetization loops are calculated over a wide range of parameters. The effects of applied magnetic field frequency f and amplitude B0 and critical current density on magnetostriction and magnetization are discussed. Results show that the critical current density of high temperature superconductor (HTS) YBCO has a significant effect on the magnetization and magnetostriction. The pinning-induced magnetostriction which has been observed in experiment can be qualitatively simulated by this model.

대면적 YBCO 고온 초전도 벌크 자석 및 조작기 개발

For the practical application of a YBCO superconductor bulk, the superconductor bulk magnet with high magnetic field on a large area surface should be fabricated. To make this, YBCO single crystal bulks with fine <TEX>$Y_2BaCuO_5$</TEX>(Y211) particles have been prepared by the top-seed melt growth(TSMG) method with <TEX>$YBa_2Cu_3O_x$</TEX>, <TEX>$Y_2O_3$</TEX>, and <TEX>$CeO_2$</TEX> mixing precursor. By using <TEX>$Y_2O_3$</TEX> instead of <TEX>$Y_2BaCuO_5$</TEX> as precursor, the manufacturing process became simpler and more economical. The microstructures, trapped field and critical current density of the various conditioned YBCO bulks have been observed, analyzed and measured. The different characteristic values of the several samples have been analyzed from the viewpoint of their microstructures. We have developed a <TEX>$8{\times}12cm$</TEX> size superconductor bulk magnet, up to 3 T class, by using the 4 T class-high field superconducting magnetizer and confirmed the applicability of the transmission level circuit breakers by measuring the strength and speed of the superconductor bulk magnet actuator.

Origin of photovoltaic effect in superconducting YBa2Cu3O6.96 ceramics.

We report remarkable photovoltaic effect in YBa2Cu3O6.96 (YBCO) ceramic between 50 and 300 K induced by blue-laser illumination, which is directly related to the superconductivity of YBCO and the YBCO-metallic electrode interface. There is a polarity reversal for the open circuit voltage Voc and short circuit current Isc when YBCO undergoes a transition from superconducting to resistive state. We show that there exists an electrical potential across the superconductor-normal metal interface, which provides the separation force for the photo-induced electron-hole pairs. This interface potential directs from YBCO to the metal electrode when YBCO is superconducting and switches to the opposite direction when YBCO becomes nonsuperconducting. The origin of the potential may be readily associated with the proximity effect at metal-superconductor interface when YBCO is superconducting and its value is estimated to be ~10–8 mV at 50 K with a laser intensity of 502 mW/cm2. Combination of a p-type material YBCO at normal state with an n-type material Ag-paste forms a quasi-pn junction which is responsible for the photovoltaic behavior of YBCO ceramics at high temperatures. Our findings may pave the way to new applications of photon-electronic devices and shed further light on the proximity effect at the superconductor-metal interface.