YBCO Research Articles

Investigation of magnetic force properties between different PMGs and multi-seeded YBCO superconductors with different seed distances

The magnetic levitation force in vertical direction and guidance force in lateral direction should be increased for enhancing the loading capacity and stability of Maglev systems, respectively. In this study, we have produced multi‒seeded YBCO (YBa2Cu3O7) superconductors with two seeds and investigated the effect of seed distance on the vertical levitation force and lateral guidance force properties by using different permanent magnetic guideway (PMG) arrangements. Although there are studies in literature related to different distance, orientation and angle of seeds; there is no detailed study investigating the effect of seed distance on the vertical and lateral magnetic force properties of Maglev systems depending on different types of PMGs. In this study, after the sample fabrication, the optimum PMG arrangement were determined by using numerical simulation to obtain magnetic flux density distribution. It is determined that both maximum levitation and guidance force values firstly increased with increasing the seed distance from 0 to 4 mm and then related forces decreased with increasing the seed distance from 4 to 16 mm but still keep the higher force values than the sample with the seed distances of 0 mm. This situation is clarified as the increasing of the seed distance to an optimum value enhances both the levitation and guidance forces simultaneously and this is very important for levitation force applications because it causes to easy control of the Maglev system in vertical and lateral directions.

Design and Comparison Analysis of 3 T Superconducting Magnets Using MgB2 and 2G HTS Wires for DC Induction Heaters

Recently, certain superconducting wires, such as second-generation high-temperature superconducting (2G HTS) and low-temperature superconducting magnesium diboride (MgB2) wires, have been used in dc induction heaters. Therefore, it is necessary to analyze and compare which wire type is better for the magnet design of a superconducting dc induction heater. This paper presents the design process and comparative analysis results of 3 T superconducting magnets for a 300-kW-class dc induction heater using 2G HTS yttrium barium copper oxide (YBCO) and MgB2 wires. The specifications of the YBCO wire and two types of MgB2 wires were investigated first. The magnets were then designed so that the maximum magnetic flux density was 3 T, and the magnetic field distributions were analyzed using a three-dimensional finite element method program. Finally, the magnet designs were compared in terms of size, magnetic flux density, operating current and temperature, winding method, required length, and wire cost. This study result will be effectively applied to a commercial 300-kW-class superconducting dc induction heater.

Design and Characteristic Analysis of a 1 MW Superconducting Motor for Ship Propulsions

Electric motors tend to be large in size because they have low speed and high torque characteristics. A superconducting motor (SCM) can be a key technology used to solve these problems. Using the characteristics of a superconductor, the SCM can reduce the volume and weight. This paper deals with the design and characteristic analysis of a 1 MW SCM for ship propulsion. An effective design of the SCM was suggested considering the electromagnetic, thermal, and mechanical properties of the motor. The SCM was designed using Y-Ba-Cu-O (YBCO) wires focusing on size, operating filed current, magnetic flux density, heat load, and mechanical stress. The current leads were also designed to minimize the heat loss in the motor, and the thermal contraction and mechanical force were calculated to design the torque tube. Electromagnetic, mechanical, and thermal characteristics were analyzed using a 3D finite element method program. As a result, the size of SCM was minimized, and the heat loss was also reduced by an effective current lead design. The designed torque tube was structurally stable with a 70% stress margin. These results will help to expand the electric propulsion motor capacity and improve the efficiency of the ship propulsion system.

Tunable Stopband HTS Josephson Junction Left-Handed Transmission Line With Independently Biasable Unit Cells

A practical coplanar Josephson junction left-handed transmission line based on a step-edge junction technique is proposed in high-temperature superconductor technology and analyzed by electromagnetic simulations. The layout is designed for monolayer Yttrium Barium Copper Oxide thin film fabrication process. The propagation stopbands are tunable by controlling bias currents of Josephson junction arrays acting as parallel inductors for unit cells of the transmission line. Unlike the reported designs, each unit cell of our left-handed transmission line is independently biasable due to dc isolation of the unit cells along the transmission line. Being individually biasable is practically important for cancelling out junction critical current nonuniformities originated from the fabrication process. Tunability of the onset frequency of the left-handed propagation regime, and the propagation stopband separating the left- and right-handed propagation regimes of the proposed device has been demonstrated by simulations, is in good agreement with theory, and is predicted to be above 15%.

Magnetic levitation and guidance performance of Y–Ba–Cu–O and Gd–Ba–Cu–O bulk superconductors under low ambient pressure

The high-temperature superconducting Maglev-evacuated tube transport (HTS Maglev-ETT) system has significant potential for practical applications. In order to employ HTS bulks in an ETT system, it is necessary to study the magnetic levitation and guidance performance of bulk superconductors under low ambient pressure conditions that are representative of those inside the tube. As a result, we have investigated the Maglev performance of Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) single grain, bulk superconductors under different ambient pressures of 100 kPa, 60 kPa and 20 kPa using a bespoke pressure-controlling platform, in which the superconductors were positioned above a Halbach permanent magnet guideway. The levitation forces under conditions of field-cooling (FC) and zero-field-cooling (ZFC) have been measured and analyzed. The guidance force for the FC case and the levitation force relaxation for the ZFC case were also measured. It was found from the experimental results that the Maglev performance of both types of bulk superconductor improves significantly by reducing the ambient pressure in their immediate working environment. The levitation forces of YBCO and GdBCO bulk superconductors were observed to increase by 11.6% and 4.4% in the case of FC, and by 20.3% and 13.7% in the case of ZFC, respectively, as the ambient pressure changed from 100 kPa to 20 kPa. An improvement of the guidance force and an inhibition of the levitation force relaxation were also observed for these materials. The supercooled liquid nitrogen cryogen in the low-pressure environment further reduces the temperature, which, in turn, increases the critical current density Jc of the bulk superconductors and improves their levitation performance. These results provide further evidence of the significant advantages of combining HTS Maglev with evacuated tube technologies as a key enabling feature of the HTS Maglev-ETT system. The data further indicate that YBCO bulk superconductors tend to be more sensitive to ambient pressure and temperature variation than GdBCO bulk superconductors. This difference essentially reflects the dependence of Maglev performance of HTS bulk superconductors on Jc when operating in a low-pressure environment.

An analytical method for predicting the net (thermal plus intrinsic) residual stresses in multilayered yttrium barium copper oxide coated conductors

In this paper, the net (thermal plus intrinsic) residual stresses in the films of American Superconductor (AMSC 344®) tape was analyzed via a displacement- energy model (DEM) solution approach. The DEM solution approach was developed to predict both the thermal mismatch and intrinsic film stresses in the coated conductor (CC) films thereby avoid the costly experiments usually required to capture the intrinsic film’s stress part in CC films. The analysis was based on the force and moment balances method, classical plate theory, and Hamaker method. On this model, the authors studied the generation of misfit strains in the CC films due to the thermal and free-vibration mismatch between the layers, and further the role of these actions in the residual stresses evolution in the CC films. The results showed that the thermal film stress in the yttrium barium copper oxide (YBCO) films calculated by the DEM solution approach was 460.80 MPa, whereas that calculated by the closed-form solution method was 455.30 MPa. Moreover, for the non-textured yttrium-stabilized zirconium (YSZ) films deposited on the Hastelloy C substrate, the calculated net residual stress by the DEM solution approach was 673 MPa, whereas the measured net residual stress by the x-ray Diffraction ( Method) was 598 ± 75 MPa. Therefore, the DEM solution approach successfully predicted the net residual stresses in the CC films analyzed because the calculated results by the DEM solution approach agree well with those by the closed-form solution and x-ray Diffraction ( methods).

AC Magnetic Susceptibility of Y3Ba5Cu8O18 Substituted by Nd3+ and Ca2+ Ions

Effect of Nd3+ and Ca2+ ion substitutions in Y3Ba5Cu8O18 (Y-358) was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity, and ac magnetic susceptibility measurements. Superconducting samples of type Y3 − xNdxBa5 − yCayCu8O18 (with 0 ≤ x, y ≤ 0.4) were synthesized by the standard solid-state reaction technique. XRD patterns revealed that all the samples were mainly composed of Y-358 phase with orthorhombic structure. SEM micrographs showed that Nd3+ and Ca2+ ion substitutions had the ability to alter the grain morphology of Y-358 to irregular randomly oriented grains with smaller average grain sizes. The temperature-dependent electrical resistivity curves indicated that the superconducting transition temperature Tc was decreased from 96.51 to 87.41 K as the substitution contents were increased from 0 to 0.4. Detailed AC magnetic susceptibility measurements were done using a quantum design physical property measurement system (PPMS) at different dc fields (B = 0.5–20 kG) and frequency of 1 kHz. A comparison between electrical resistivity and AC magnetic susceptibility data was performed. It was found that Tcs obtained from AC magnetic susceptibility were much lower than those obtained from the resistivity measurements, for all studied samples. This was discussed in terms of filamentary paths that could produce sharp pronounced drops in diamagnetism. Generally, the depression in Tc was attributed to the decrease in relative volume fraction of Y-358 or due to trapping of mobile holes or other mechanism connected with oxygen vacancy disorder. Werthamer–Helfand–Hohenberg (WHH) theory was employed to study the temperature dependence of the upper critical magnetic field Bc2(T) for the samples. The relative importance of both orbital and paramagnetic effects in the suppression of superconductivity was described with the aid of Maki parameter (κM). The estimated values of the upper critical magnetic field at 0 K, Bc2(0), were found to decrease from 37.3 to 13.5 T as Nd3+ and Ca2+ contents were increased from 0 to 0.4. This decrement was attributed to the weak electron–phonon coupling and to the orbital as well as spin pair breaking mechanisms. Furthermore, Ginzburg–Landau coherence length ξGL of Y3 − xNdxBa5 − yCayCu8O18 was found to increase with the increase of the Nd3+ and Ca2+ contents. Therefore, Nd3+ and Ca2+ ions play an important role in the pair-breaking mechanism and in suppressing superconductivity of the Y-358 phase.

Cryogen-free variable temperature scanning SQUID microscope

Scanning Superconducting QUantum Interference Device (SQUID) microscopy is a powerful tool for imaging local magnetic properties of materials and devices, but it requires a low-vibration cryogenic environment, traditionally achieved by thermal contact with a bath of liquid helium or the mixing chamber of a "wet" dilution refrigerator. We mount a SQUID microscope on the 3 K plate of a Bluefors cryocooler and characterize its vibration spectrum by measuring SQUID noise in a region of sharp flux gradient. By implementing passive vibration isolation, we reduce relative sensor-sample vibrations to 20 nm in-plane and 15 nm out-of-plane. A variable-temperature sample stage that is thermally isolated from the SQUID sensor enables the measurement at sample temperatures from 2.8 K to 110 K. We demonstrate these advances by imaging inhomogeneous diamagnetic susceptibility and vortex pinning in optimally doped yttrium barium copper oxide above 90 K.

Mechanical Damage of YBa2CU3O7-Coated Conducting Film Caused by Its CeO2 Interface with Defects

YBa2Cu3O7 (YBCO) multilayer coating conductors are the second generation superconductor wires. The interface structure plays an important role in the performance of the material, especially that between the superconducting layer and the CeO2 buffer layer. The YBCO/CeO2 interface is not only very critical on the atomic scale for effectively modulating the polycrystalline structure of YBCO, but also, as weak connection on the macro level, profoundly affect macro physical properties of the whole film, for example, mechanical toughness. Generally, most defects at the YBCO/CeO2 interface are generated during the fabrication, and further develop when the film is wound or in the process of current carrying. These defects, at different level, lead to mechanical damage even under simple deformations such as tension and bending. In this work, by way of atomistic computer simulations with the molecular dynamics (MD), a two-dimensional YBCO/CeO2 interface atomic model was developed and validated. On this interface model, the damage propagation on the atomic-scale and further analysis with stress and potential energy especially affected by the YBCO/CeO2 interface with/without defects under the tension and bending have been comprehensively investigated. As a result, we not only visualized the simulated damage process and route on the YBCO/CeO2 interface, but also more importantly, combined with the variation of macro properties, deeply analyzed the damage mechanism caused by the interface and its defects.

Comparative study of one-dimensional photonic crystal heterostructure doped with a high and low-transition temperature superconducting for a low-temperature sensor

In this work, we present a theoretical study dealing with the sensitivity to physical parameters such as defect nature and thickness, and temperature. Indeed, the sensitivity considerably enhanced via the use of one-dimensional photonic crystal heterostructure (1D-PCH) which is composed of a few layers of ordinary materials, and superconducting defects. The aim of this paper is to compare the sensitivity of two proposed models consisting of (a) 1D-PCH doped with a high-transition temperature superconductor (Yttrium barium copper oxide (YBCO)), and (b) 1D-PCH doped with a low-transition temperature superconductor (niobium nitrure (NbN)). By using the transfer-matrix method (TMM), it has been demonstrated that model (b) is very sensitive compared to model (a). Therefore, the superconducting defect nature on 1D-PCH, using a few layers can play a fundamental role in a very low-temperature sensor.

Tunable narrowband optical filters using superconductor/dielectric generalized Thue-Morse photonic crystals

A narrowband tunable transmission optical filters according to hybrid dielectric/ superconductor quasi-photonic structures are designed using the transfer-matrix method (TMM) and The two-fluid model. The structure layers are arranged using Generalized Thue-Morse (GTM) sequence and made of Yttrium Barium Copper Oxide (YBCO) and SiO2 materials. Multi-transmission peaks and sub-photonic-band-gaps (SPBG) can be generated inside the basic photonic-band-gap (PBG) and can be manipulated by the Thue-Morse sequence parameters, the layers' thickness and the operating temperature of superconductors. Also by applying a deformation law on the layers' thickness, the width of the sub-photonic-band-gaps can be enlarged. The designed structures can be used as a tunable multichannel filters, temperature sensing and can be very useful in the optical-communication field.

Control of nanostructure and pinning properties in solution deposited YBa2Cu3O7\u2212x nanocomposites with preformed perovskite nanoparticles

Solution deposited YBa2Cu3O7−x (YBCO) nanocomposites with preformed nanoparticles represent a promising cost-effective approach for superior critical current properties under applied magnetic fields. Nonetheless, the majority of YBCO nanocomposites with high nanoparticle loads (>20%) suffer from nanoparticle coalescence and degraded superconducting properties. Here, we study the influence of nanoparticle concentration (0–25% mol), size (5 nm–10 nm) and composition (BaHfO3, BaZrO3) on the generation of structural defects in the epitaxial YBCO matrix, key parameter for vortex pinning. We demonstrate that flash-heated superconducting nanocomposites with 20 mol% preformed BaHfO3 or BaZrO3 perovskite secondary phases feature discrete and small (7 nm) nanoparticles and high density of YBa2Cu4O8 (Y248) intergrowths. We identify a synergy between Y248 intergrowth density and small nanoparticles to increase artificial vortex pinning centers. Also, we validate the multideposition process to successfully increase film thickness of epitaxial nanocomposites with competitive critical currents Ic at 77 K.

Operation of YBCO kinetic-inductance bolometers for outer solar system missions

We developed superconducting kinetic inductance bolometers (KIBs) for hyperspectral imaging in outer solar system missions. Each bolometer is a microwave L-C resonator that will act as an individual pixel in the focal plane of an imaging Fourier transform infrared spectrometer. Our devices are fabricated from high temperature superconductor yttrium barium copper oxide (YBCO), with a superconducting transition temperature of ∼85 K. The inductors are suspended on thin Si3N4 membranes. Each resonator operates at a unique resonant frequency, and hence, many can be multiplexed on a single feed line using a large number of carrier frequencies. The resonators function as detectors because their resonant frequencies decrease with increasing temperature as the bolometers absorb incident radiation. In this paper, we discuss the thermal properties of a YBCO KIB and its response to signal power to verify that the response is near theoretical predictions.

Magnetic Shielding of Open and Semi-closed Bulk Superconductor Tubes: The Role of a Cap

In this paper we investigate the magnetic shielding of hollow and semi-closed bulk superconducting tubes at 77 K. We first consider the properties of a commercial Bi-2223 tube closed by a disk-shaped cap placed against its extremity. The results are compared with those obtained on a bulk large grain Y-Ba-Cu-O (YBCO) tube produced by buffer-aided top seeded melt growth. In this process, the disk-shaped pellet and the tubular sample are grown together, resulting in a tube naturally closed at one extremity. The field to be shielded is either parallel or perpendicular to the main axis of the tube. The experimental results are compared with the results of finite element numerical modeling carried out either in two dimensions (for the axial configuration) or three dimensions (for the transverse configuration). In the axial configuration, the results show that the shielded volume can be enhanced easily by increasing the thickness of the cap. In the transverse configuration, the results show the critical role played by the superconducting current loops flowing between the tube and the cap for magnetic shielding. If the tube and the cap are separated by a non-superconducting joint or air gap, the presence of a cap leads only to a small improvement of the transverse shielding factor, even for a configuration where the gap between the cap and the tube contains a 90° bend. The cap leads to a significant increase in the transverse shielding when the cap and the tube are naturally grown in the same process, i.e., made of a continuous superconducting material. The experimental results can be reproduced qualitatively by 3-D numerical modeling.

Magnetic field sensing with the kinetic inductance of a high-Tc superconductor

We carry out an experimental feasibility study of a magnetic field sensor based on the kinetic inductance of the high critical temperature (high-Tc) superconductor yttrium barium copper oxide. We pattern thin superconducting films into radio-frequency resonators that feature a magnetic field pick-up loop. At 77 K and for film thicknesses down to 75 nm, we observe the persistence of screening currents that modulate the loop kinetic inductance. We report on a device with a magnetic field sensitivity of 4 pT/Hz, an instantaneous dynamic range of 11 μT, and operability in magnetic fields up to 28 μT. According to the experimental results the device concept appears attractive for sensing applications in ambient magnetic field environments.

A Review on Cuprate Based Superconducting Materials

When Bednorz and Müller discovered the superconductivity in a compound La-Ba-Cu-O in 1986, it was considered as a breakthrough in the research of the superconductivity. This leads to the discovery of the other cuprate superconductors, and immediately the transition temperature of the synthesized materials reached to the liquid nitrogen temperature. Today the maximum transition temperature of the cuprate superconductors changes from 35 K for La2 −xSrx CuO4 to 138 K for Hg1−xTlx Ba2 Ca2 Cu3 Oy (the highest record under normal pressure, which extends to ∼160K at high pressure). High-temperature superconductivity in the Non-stoichiometric cuprate lanthanum barium copper oxide . The Tc for this material was 35 K, well above the previous record of 23K. Thousands of publications examine the superconductivity in cuprates between 1986 and 2001, and Bednorz and Müller were awarded the Nobel Prize in Physics only a year after their discovery. From 1986 to 2008, many cuprate superconductors were identified, the most famous being yttrium barium copper oxide (YBa2 Cu3 O7 , "YBCO" or "1-2-3"). Another example is bismuth strontium calcium copper oxide (BSCCO or Bi2 Sr2 Can Cun+1O2n+6-d ) with Tc = 95–107 K depending on the n value. Thallium barium calcium copper oxide (TBCCO, TlmBa2 Can−1Cun O2n+m+2+δ ) was the next class of high-Tc cuprate superconductors with Tc = 127 K observed in Tl2 Ba2 Ca2 Cu3 O10 (TBCCO-2223) in 1988. The highest confirmed, ambient-pressure, Tc is 135 K, achieved in 1993 with the layered cuprate HgBa2 Ca2 Cu3 O8+x. few months later, another team measured superconductivity above 150K in the same compound under applied pressure (153 K at 150 k bar).

Effect of Different Nano-sized MgO Addition on YBa2Cu3O7-δ Superconductor

The effect of nanoparticle with different size on a superconductor is interesting because the size of the coherence length, penetration depth, and the magnetic flux in a superconductor is in the nanometer range. In this paper, we report the effects of different nano-sized MgO (20, 40, and 100 nm) addition on YBa2Cu3O7-δ(MgO)x for x = 0, 0.1, and 0.2 wt.%. X-ray diffraction patterns indicated a single YBa2Cu3O7 (YBCO) phase where the peaks were shifted to larger angles in the 20- and 40-nm MgO-added samples indicating induced stress of first order in the structure. The electrical resistance versus temperature was measured using the four-probe method. The transition temperature, Tc, for the pure YBCO showed Tc = 90 K and was suppressed to 78–80 K for the 20- and 40-nm MgO-added samples. AC susceptibility (χ = χ′ + iχ″) measurements showed a shift in the peak temperature, Tp, of the imaginary susceptibility χ″ towards lower temperatures for 20-nm MgO-added samples but increased with larger MgO (100 nm). This work showed that smaller nano-sized MgO suppressed the superconducting properties of YBCO more compared with the larger MgO.

The remarkable difference in water wettability of YBa2Cu3O7−x and Y2BaCuO5 powders

The irreversible deterioration in superconducting performance caused by the reactions with air moisture is a severe obstacle for the applications of Y-Ba-Cu-O (YBCO) superconductors. However, the detailed water adsorption mechanism and the crack growth behaviors in superconductors are still not very clear. In this study, YBa2Cu3O7−x (Y123) and Y2BaCuO5 (Y211) powders are fabricated by chemical coprecipitation method for experiments. An optical contact angle measuring device is used to analyze the water wettability of powders. The results demonstrate that Y123 powders are super hydrophilic while Y211 powders are hydrophobic. The concomitant difference in surface energy of powders results in a large number of crystal spaces between Y211 particles and Y123 grain domain after crystal growth. Such crystal spaces are the vulnerable parts for air moisture. A deterioration and crack-growth mechanism of YBCO superconductors under air moisture is proposed and discussed accordingly.

Performance comparison of 1X versus 4X HTS tapes toward the design a 10‐MW direct drive HTS generator for wind turbine applications

AbstractWith current developments underway at the University of Houston, 4× high‐temperature superconducting (HTS) yttrium barium copper oxide (YBCO) tapes are expected to reach a fourfold critical current density improvement at 30 K and 3 T as part of an Advanced Research Projects Agency‐Energy (ARPA‐E)‐sponsored project. The impetus for this project is to develop and deploy cost‐effective direct drive HTS generators for large offshore wind turbine generators. The improved conductor performance of 4× tapes over 1× tapes is projected to allow for a significant reduction in the amount of HTS tapes required to generate the excitation field and, thus, lead to a reduction of the overall generator cost. It was, however, deduced from simulation results that conventional methods of rotor field enhancement using rotor iron makes 1× conductor competitive enough compared with 4× conductors; hence, commercially available YBCO tapes can provide all the energy density requirements to make wind turbines a competitive energy resource based on energy forecasts. This paper is a presentation of design and optimization work to find the best generator topology from the point of view of both machine design and electricity supply. The generators are numerically modeled and simulated using 1× and 4× YBCO HTS conductors on either or of both the rotor and stator side of the generators.

Activation energy of oxygen diffusion: A possible indicator of supercurrents through YBa2Cu3O7 grain boundaries

Oxygen diffusion is the main transportation form during the preparation process of polycrystalline superconductor YBa2Cu3O7 (YBCO) thin films. Especially the diffusion of oxygen ions in grain boundaries (GBs) can lead to the formation of oxygen vacancies, and finally have an impact on the critical current density (Jc) of YBCO conductors. To deeply understand the supercurrent-limiting mechanism of GBs, for an YBCO bicrystal (containing a single GB), in this article we intensively studied the diffusion of oxygen ions through GB region by molecular dynamics simulations. The calculated results show that the oxygen diffusion in the YBCO bicrystals can be enhanced in GBs, and specifically which is closely related to the grain boundary angle (θ). The most interesting finding is that the activation energy of oxygen diffusion shows an exponential fall with the grain boundary angle, which is exactly consistent with the relation of the critical current density versus the grain boundary angle (Jc ~ θ) in GBs. We firmly believe that the activation energy of oxygen diffusion should have an essential relevance with the Jc especially in YBCO GBs, and can be as an indicator for predicting supercurrents. For these results we further gave an in-depth discussion.