High-temperature Superconductor Samples Research Articles

Experimental study on AC loss of 1G and 2G HTS coils with an identical structure, geometry and number of turns

Devices made of High Temperature Superconductor (HTS) will suffer AC loss during AC operations, which has unnegligible influence on energy consumption, overall efficiency, cooling cost, and operational stability of the devices. In this study, comparative measurements on 1G and 2G HTS coil samples with an identical structure, geometry, and number of turns were systematically conducted with a calorimetric method at different current values (I rmss) and frequencies (fs). The AC loss characteristics of the HTS samples were analyzed and compared based on the experimental results. The results show that eddy current and coupling play a more dominant role than magnetic hysteresis in the total AC loss of coils made of HTS tapes. The AC loss of both samples increases with I rms and f, but the AC loss is more sensitive to I rms than to f. Under the same conditions, the 1G coil sample has a slightly larger AC loss than the 2G one.

Detection of Radiation Generated by Moving Josephson Vortices in a Bi<sub>2 +</sub> <sub><em>x</em></sub>Sr<sub>2 –</sub> <sub><em>x</em></sub>CuO<sub>6 + δ</sub> Single Crystal in High Magnetic Fields Directly in the Sample

A high-temperature superconductor sample with numerous internal Josephson junctions formed by atomic layers is a nonlinear system with unique dynamic properties. An external magnetic field penetrates in the sample in the form of moving Josephson vortices, which generate radiation. It has been shown that this radiation in a Bi2 +xSr2 –xCuO6 + δ(Bi2201) single crystal can be detected by means of a Josephson junction on a microbreak (break junction) directly inside the single crystal.

Point-Contact Spectroscopy in Bulk Samples of Electron-Doped Cuprate Superconductors.

Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd2-xCexCuO4-δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with Ce content x = 0.15 showed the absence of spurious phases and randomly oriented grains, most of which had dimensions of approximately 220 µm2. The low-bias spectra in the tunneling regime, i.e., high-transparency interface, exhibited a gap feature at about ±5 meV and no zero-bias conductance, despite the random oriented grains investigated within our bulk samples, consistent with most of the literature data on oriented samples. High-bias conductance was also measured in order to obtain information on the properties of the barrier. A V-shape was observed in some cases, instead of the parabolic behavior expected for tunnel junctions.

Graphene doping effects on the magnetic and transport properties of YBa2Cu3O7-δ high temperature superconductor

In this work, bulk graphene-doped YBa2Cu3O7-δ (YBCO) high-temperature superconductor samples were prepared with composition of YBCO + x wt.% graphene nanoplatelets (G) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The X-ray diffraction patterns show the YBCO orthorhombic phase in all the samples. The SEM images show good grain connectivity between YBCO grains in graphene-doped samples. Furthermore, the broadening of resistivity under applied magnetic fields up to 9T and thermally activated flux creep in the mixed state were studied using Arrhenius plots. The activation energy U0 (H) increased with graphene doping results in better flux pinning and higher critical current densities. Moreover, improvement in the critical temperature (TC), upper critical field (μ0HC2) and the irreversibility field (μ0Hirr) were observed in graphene-doped samples as compared to the pure YBCO sample.

The magnetic and levitation characteristics of single-grain YBaCuO and GdBaCuO-Ag bulk superconductors in high magnetic fields

In principle, high-temperature superconducting (HTS) flux-pinning maglev has the advantage of self-stable levitation and is therefore a good development prospect as a new rail transit technology. The magnetic field intensity is one of the key factors affecting the levitation performance of single-grain bulk superconductors in the HTS maglev system. To date, however, most researchers have focused on the levitation performance of HTS bulk superconductors in magnetic fields within a permanent magnet guideway (PMG) configuration. The magnitude of the external working magnetic field provided by a PMG is limited to about 0.5 T at 77 K, given that the superconductor usually levitates at a typical working height of 10 mm above the PMG. Therefore, the weak magnetic fields generated by the PMG significantly limits the levitation performance of HTS maglev systems to that of the permanent magnet (PM). In this article, a superconducting magnet test bench was utilized to provide a 0–3 T external magnetic field (B) environment for the study of the levitation force in HTS single grains. The difference in levitation performance between YBaCuO (YBCO) and GdBaCuO-Ag (GdBCO-Ag) bulk superconductors under large, changing magnetic fields was studied systematically. The relationships between levitation force and magnetic field characteristics, including vertical magnetic field component (Bz), transverse magnetic field component (Br), and vertical magnetic field variation (ΔBz) were investigated. The result of variation curves about YBCO and GdBCO bulks' levitation forces under different ΔBz shows that the levitation force of the bulk, single-grain superconductors will reach saturation under a varying ΔBz environment (0.72 and 1.5 T). The values of ΔBz corresponding to the saturation positions are found to be independent of the sizes of the HTS samples. At the same time, GdBCO-Ag exhibits a levitation force that is 112.8% greater than YBCO in B = 3 T magnetic environment. As a result, it is demonstrated that the levitation potential of single-grain HTS bulks can be better exploited by optimizing the distribution of the magnetic field.

Универсальность поведения гистерезиса магнитосопротивления и его температурной эволюции для гранулярных высокотемпературных сверхпроводников Y-Ba-Cu-O

The work is devoted to the establishment of regularities in the behavior of the magnetoresistance hysteresis R(H) of granular high-temperature superconductors (HTS) of the yttrium system. We carried out a comparative study of the magnetotransport properties of granular HTSC samples, which have (i) approximately the same magnetic properties and temperatures of the onset of the superconducting transition (90.5–93.5 K, which characterizes HTS grains) and (ii) different values of the transport critical current JC (which characterizes the intergrain boundaries). Despite the significant scatter in the JC values (more than an order of magnitude) of the three samples studied, a universal behavior of the magnetoresistance hysteresis was found, apparently inherent in all granular Y-Ba-Cu-O. The R(H) hysteresis is very wide, and in a sufficiently large interval of the external field, the dependence of the hysteresis width of the magnetoresistance H on the field Hdec (external field H = Hdec for a decreasing hysteresis branch) is close to a linear function: H ≈ Hdec. This behavior is observed for the entire temperature range of realization of the superconducting state (the studies were carried out at temperatures of 77–88 K and 4.2 K). The explanation of the obtained result is based on the concept of consideration the effective field in the intergrain boundaries. This effective field is the superposition of the external field and the field induced by the magnetic moments of the grains. The field induced by the grains, in turn, is significantly enhanced in the region of intergrain boundaries due to the effect of the magnetic flux compression (the length of the intergrain boundaries is several orders of magnitude smaller than the size of the HTS grains). The above is confirmed from the analysis of the R(H) hysteresis for a composite HTS sample based on Y-Ba-Cu-O and CuO, in which the length of the intergranular boundaries is purposefully increased, as a result, the effect of the flux compression is less pronounced, and the hysteresis R(H) narrows.

The Effect of Addition of (Al2O3) Nano Particles on Structural and Electrical Properties of Bi2Ba2Ca2Cu3O10" +δ" Superconductors at High Temperature

To enhancement the superconductor structural characteristics, nanoparticles of the Al2O3 were added to the samples under study. The Samples of high temperature superconductors 1-X (Bi2Ba2Ca2Cu3O10+ ) + X(Al2O3) with X= (0-0.9) were prepared by solid state reaction method under hydraulic pressure 8 ton/cm2 and annealing temperature 800 . Electrical properties of the samples showed that Tc increases from 126 K to 139 K, and also oxygen content in samples increased with increasing X values from 0 to 0.5, while Tc decreased less than 77 K with increasing X at values more than 0.5. In Structural properties, the X-ray diffraction of the samples showed orthorhombic phase with a=4.286A , b=5.4184A , c=35.3528A at X=0, while c-value is increased to 35.9848A at X=0.5. AFM results shows that the average grain size of the best sample was 47.67 nm at X=0.5. SEM it showed that there are dark regions related to the heavier elements, such as Bi and Cu, and light regions related to lighter elements, such as Ba and Ca, depending on atomic weights

Forming High-Temperature Superconducting Layers at the Interfaces between Nonsuperconducting Phases

An alternative technique for synthesizing high-temperature superconductor samples is proposed, in which superconducting layers should form on the surface of hard-melting Ho2BaCuO5 green phase grains immersed in the liquid phase BaCuO2 + CuO.

Comparison of properties of a bulk HTS and a stack of HTS tapes after FC and ZFC

This paper presents the results of the analysis of properties of a high-temperature superconducting (HTS) material in two forms - HTS bulks and a stack made of a number of HTS tape layers. Stack of HTS tape is a new type of application of superconductors, which can be used instead of a convention bulk material. In this work, we study the levitation properties of HTS stack and compare it with the same characteristics of HTS bulks to find the effective way of modelling such type of HTS. Experimental measurements of the force interaction between a permanent magnet and HTS material, as well as a "trapped" magnetic field, are performed for both types of a superconductor. The HTS samples are analysed in the case of Field Cooling (FC) and Zero Field Cooling (ZFC). The aim of the research is to analyse experimental results to compose and justify mathematical models for calculation magnetic system with such types of superconductor.

Формирование высокотемпературных сверхпроводящих слоев на границах несверхпроводящих фаз

An alternative method for the synthesis of samples of high-temperature superconductors (HTSCs) is proposed, in which nanoscale superconducting layers should form on the surface of refractory granules of the “green phase” Ho2BaCuO5 immersed in the liquid phase BaCuO2 + CuO.

Modification of a Second-Generation HTS Tape Based on GdBCO(123) under Pulsed Electron Beam Irradiation

Samples of composite second-generation high-temperature superconducting (HTS) tapes based on the GdBCO (123) compound have been irradiated in a pulsed electron accelerator (system Terek-2, GPI RAS) through a tantalum target in order to determine how the thermal and shock loads arising on the tantalum-HTS interface affect the superconducting parameters of HTS tapes. Scanning Hall magnetometry was applied to characterize HTS samples subjected to electron irradiation. The thermal modes and shock load in a composite superconductor under irradiation are estimated as functions of the energy absorbed by the target. At a silver surface temperature equal to the melting point, the critical current decreases by 87% from the initial value. At lower irradiation energies, the decrease in the critical current is smaller. The role of the temperature effects and shock waves under this irradiation is discussed.

The Effect of Zinc on the Structural, Electrical, and Mechanical Properties of YBCO-123 Superconducting Nanoparticles Prepared by an Acetate-Based Sol-Gel Process

In this study, zinc (Zn)-doped YBaCuO (YBCO)-123-based high-temperature superconducting samples were produced using the sol-gel method, which is commonly used for preparing nanosize materials. Zn ions were substituted by Cu ions (YBa2Cu3-xZnxO), and Zn doping effects on structural, electrical, and mechanical properties of the YBCO-123 superconductors were examined in detail. Undoped sample was prepared under same conditions. X-ray diffraction analysis (XRD) was used to determine phase analysis and lattice parameters of the superconducting samples. To analyze the microstructure properties, scanning electron microscope (SEM) measurements were performed. Resistivity and microhardness measurements were also carried out for superconducting and mechanic properties, respectively. Vickers microhardness, young modulus, fracture toughness, and yield strength values of the samples were calculated. Microhardness measurements were analyzed using the Kick’s law, proportional sample resistance (PSR) model, EPD model, the Hays-Kendall (HK) approach, and indentation-induced cracking (IIC) model.

Magnetoresistance Hysteresis Evolution in the Granular Y–Ba–Cu–O High-Temperature Superconductor in a Wide Temperature Range

The temperature evolution of the magnetoresistance hysteresis in the granular YBa2Cu3O7-δ high-temperature (TC ≈ 92 K) superconductor has been investigated. The measurements have been performed in the high-temperature region (78–90 K) and at the liquid helium temperature (4.2 K). The results obtained have been analyzed using the developed model of the behavior of transport properties of a granular high-temperature superconductor in an external magnetic field. Within the discussed model, the dissipation of the grain boundary subsystem is determined by the intergrain spacing-averaged effective field Beff, which is a superposition of external field H and the field induced by the magnetic moments of superconducting grains. Such a consideration yields the expression Beff(H) = H − 4πM(H) α for the effective field in the intergrain medium, where M(H) is the experimental hysteretic dependence of magnetization and α is the parameter of magnetic flux crowding in the intergrain medium. Here, the magnetoresistance is assumed to be proportional to the absolute value of the effective field: R(H) ~ |Beff(H)|. Analysis of the experimental R(H) and M(H) dependences obtained under the same conditions for the investigated high-temperature superconductor sample showed that in the high-temperature region this parameter is α ≈ 25. At the low temperature (4.2 K), we may state that the degree of flux crowding increases and the estimated α value is ~ 50. The estimates made are indicative of the strong effect of flux compression in the intergrain medium on the magnetotransport properties of the investigated granular high-temperature superconductor system. Possible reasons for a discrepancy between the developed model concepts and experimentally observed low-temperature R(H) hysteresis are analyzed.

Dissipation in granular high-temperature superconductors: New approach to describing the magnetoresistance hysteresis and the resistive transition in external magnetic fields

An approach to describing the R(H) magnetoresistance hysteresis in granular high-temperature superconductors and behavior of the R(T) resistive transition in these objects in an external magnetic field is proposed. The dissipation is attributed to the subsystem of intergrain boundaries, which form a Josephson junction network. The approach is based on accounting for the effect of magnetic moments of superconducting grains on the resulting (effective) field in the intergrain medium. The described procedure includes (i) establishing of the degree of magnetic flux crowding in the intergrain medium by comparing the experimental data on the R(H) magnetoresistance hysteresis and magnetization M(H), (ii) determining the effective field Beff in the intergrain medium as a function of external field H and temperature T with regard to the thermomagnetic prehistory, and (iii) fitting the experimental R(H) and R(T) dependences using the Arrhenius expression R ∼ exp(–EJ/ kB T), where EJ is the parameter corresponding to the Josephson coupling energy. The fundamental novelty of the proposed approach is the extraction of the functional dependences of EJ on the effective field Beff in the intergrain medium rather than on the external field H, as was made in many previous works. It is shown that the proposed approach makes it possible to adequately describe both the R(H) hysteretic dependences and R(T) dependences of the Y-Ba-Cu-O high-temperature superconductor samples with different morphologies and critical current densities.

Resonant X-ray diffraction studies on modulation structures of high temperature superconducting sample Sr<sub>2</sub>CuO<sub>3.4</sub>

<sec>Sr<sub>2</sub>CuO<sub>3+<i>δ</i></sub> is cuprate, a high temperature superconducting (HTS) material that has a single copper oxide layer and a relatively high critical temperature. Its structure is simple and contains fewer atoms, but there are many modulation structures in it. A lot of studies have pointed out that the modulation structure is related to its superconductivity. In order to further study the relationship between modulated structure and superconductivity in Sr<sub>2</sub>CuO<sub>3.4</sub> HTS sample, a new explanation for the formation mechanism of modulation structure is proposed in this paper. </sec><sec>The synchrotron radiation resonant X-ray diffraction (RXD) technique is used to detect the variation of modulation structure near the absorption edge of Cu atom. Cu<sup>2+</sup>, Cu<sup>3+</sup> valence order is detected and used to explain the formation mechanism of modulation structure in Sr<sub>2</sub>CuO<sub>3.4</sub> high temperature superconducting sample. The energy values of incident light are selected to be 8.52, 8.95, 8.98, 9.05, 9.5, and 10.0 keV near the edge of Cu <i>K</i>. The energy resolution is about 1.5 eV. The detector used in the experiment is Mar165 CCD surface detector. The distance from the detector to the sample is about 315 mm. The two-dimensional diffraction pattern recorded by the CCD plane detector is processed by Fit2D software to obtain the diffraction integral intensity. In addition, the energy calibration for each of the copper foil samples is carried out prior to the start of the experiment and in the process of varying energy value.</sec><sec>The experimental results show that the Bragg diffraction peaks corresponding to <i>T</i><sub>c</sub> = 48 K and the modulation structures of <i>Fmmm</i> and <i>Pmmm</i> are visible and calibrated. The intensity of the corresponding (2/5, 4/5, 0) diffraction peak of <i>Fmmm</i> is energy-dependent near the Cu <i>K</i> edge and first increases and then decreases abruptly near the absorption edge. This indicates that a stable ordered arrangement structure of Cu<sup>2+</sup> and Cu<sup>3+</sup> is formed at this time. The weak diffraction signal of this ordered arrangement structure confirms the fact that the copper-O bonding is stronger.</sec><sec>The experiments indicate that oxygen vacancies occupy both the apical position and the CuO<sub>2</sub> plane. The ordering arrangement of oxygen vacancies results in the ordering of copper ions with variable valence. The Cu<sup>2+</sup>, Cu<sup>3+</sup> valence order is related to the superconductivity of Sr<sub>2</sub>CuO<sub>3.4</sub>.</sec>

Magnetodynamic Studies of Fine-Crystalline YBa2Cu3Oy High-Temperature Superconductor Samples Synthesized by the Sol–Gel Method

Measurements of the complex magnetic susceptibility as a function of the temperature, alternating field amplitude, and the parallel applied constant field values for a series of YBa2Cu3Oy high-temperature superconductor samples synthesized by two different methods using of the sol–gel technology have been carried out. Regularities in the change of crystalline sizes and critical superconducting parameters are determined depending on the synthesis conditions. For all the samples, both the average temperatures of the transition to the superconducting state and their ranges, which characterize the homogeneity of the sample, remain at the level of the maximum values achievable for this compound. It is concluded that different types of the nanoscale inhomogeneity of the crystalline structure manifest themselves in the differences of the temperature dependences of the transport critical current. Means of further improving the sol–gel method for producing fine-grained ceramics with desired properties are outlined.

Maximum Endurance Lightning Current of Different High-Temperature Superconducting Wires

The over-current performance of high-temperature superconductors (HTSs) has been well studied. However, the superconducting devices used in power grid might also suffer lightning current. In previous researches, we have investigated the influences of the substrate layer, encapsulation layer, and tape dimension on the thermal stability of yttrium barium copper oxide (YBCO) tapes after suffering a lightning current. However, in this paper, we will focus on the maximum endurance lightning currents (MELCs) of different HTS tapes including YBCO and BSCCO tapes. We prepared and tested seven HTS samples. The critical current and n value of each sample were measured and calculated before and after the 8/20-μs lightning current tests. A maximum endurable value of lightning current which might not cause the critical current degradation was obtained from the testing results. Finally, the mechanisms causing the degradation were analyzed.

High temperature superconductors for fusion at the Swiss Plasma Center

High temperature superconductors (HTS) may become in future an option for the superconducting magnets of commercial fusion plants. At the Swiss Plasma Center (SPC) the R&D activity toward HTS high current, high field cables suitable for fusion magnets started in 2012 and led in 2015 to the assembly of the first 60 kA, 12 T prototype conductor. The cable concept developed at the SPC is based on the principle of ‘soldered, twisted stacks’ of REBCO tapes. The required number of stacks is assembled in a cored flat cable, cooled by forced flow of supercritical helium. The sample environment of the test facility at SPC has been upgraded with a HTS adapter and a counter-flow heat exchanger to allow testing the HTS sample in a broader range of temperature (4.5 K–50 K) using the existing, NbTi based superconducting transformer and the closed loop refrigerator.

A Study on Critical Current of Twisted Soldered-Stacked-Square (3S) HTS Wire with 1mm Width

In high temperature superconducting (HTS) applications, the external magnetic field affects the performance of the critical current and the AC loss. To improve the performance, a novel soldered-stacked-square (3S) HTS wire is developed through narrowing, stacking and soldering processes using 2G narrow wires with 1 mm width. In this paper, the narrowing process of the wire with 4 mm width was showed and the stacking and soldering processes were also presented. The 3S wire was made of three narrow HTS tapes and four brass strips. For the 3S HTS samples, the typical electrical and mechanical properties have been tested. Based on that, single 3S wire and double 3S wires were twisted. Then the critical currents of the samples were tested at different twist pitches. The test results showed that the measured critical currents of 3S wire samples were between 120 A and 150 A. The critical current of the single 3S wire at average twist pitch of 50∼70 mm was about 8% lower than that of the original wire. And the critical current of double 3S wires was about 10% lower than the original critical current at a twist pitch of 65 mm.

Anisotropy of the magnetoresistive properties of granular high-temperature superconductors resulting from magnetic flux compression in the intergrain medium

To elucidate the origin of the well-known anisotropy of the magnetoresistive properties of granular high-temperature superconductors (HTSs), which is related to the mutual orientation of magnetic field H and transport current j, we investigate the hysteretic dependences of magnetoresistance R(H) of the yttrium HTS sample at the perpendicular (H ⊥ j) and parallel (H || j) configurations. The hysteretic R(H) dependences are analyzed using the concept of the effective field in the intergrain boundaries through which superconducting current carriers tunnel. The effective degree of magnetic flux compression in the intergrain medium at the perpendicular configuration was found to be twice as much as at the parallel one. This approach explains well the anisotropy of the magnetoresistive properties of granular HTSs, which was previously reported by many authors, and the temperature dependences of the resistance in the resistive transition region.