Composite Superconductors Research Articles

Structure-Mechanical Property Relationships in Carbon Nanotube Yarns

Carbon nanotube (CNT) is an innovative material with significant potential for a wide range of applications, including but not limited to the development of lightweight composite materials or superconductors. A single CNT demonstrates an exceptional degree of tensile strength. CNTs are commonly employed in a structure of yarn, wherein several CNT strands are arranged and aligned together. CNT yarns, on the other hand, have a lower tensile strength than individual CNTs due to the different parameters of the yarn. This study aimed to investigate the effect of different structural parameters on the mechanical properties of CNT yarn. Sixty CNT yarn models with different structures were simulated with the molecular dynamic (MD) simulation. The varied parameters are the chirality of the CNTs, CNTs’ inner diameter, number of walls, crosslink density, and yarn twist angle. Tensile strength results from the simulations were compared concerning the varied parameters, and their influence on the nominal tensile strength of the CNT yarn was studied. It was found that the parameters for the CNT yarn that yields a higher tensile strength are the armchair type CNT with a small diameter, a large number of walls, crosslink density higher than approximately 1%, and a low twist angle.

Quench protection for high-temperature superconductor cables using active control of current distribution

Superconducting magnets of future fusion reactors are expected to rely on composite high-temperature superconductor (HTS) cable conductors. In presently used HTS cables, current sharing between components is limited due to poorly defined contact resistances between superconducting tapes or by design. The interplay between contact and termination resistances is the defining factor for power dissipation in these cables and ultimately defines their safe operational margins. However, the current distribution between components along the composite conductor and inside its terminations is a priori unknown, and presently, no means are available to actively tune current flow distribution in real-time to improve margins of quench protection. Also, the lack of ability to electrically probe individual components makes it impossible to identify conductor damage locations within the cable. In this work, we address both problems by introducing active current control of current distribution between components using cryogenically operated metal-oxide-semiconductor-field-effect transistors (MOSFETs). We demonstrate through simulation and experiments how real-time current controls can help to drastically reduce heat dissipation in a developing hot spot in a two-conductor model system and help identify critical current degradation of individual cable components. Prospects of other potential uses of MOSFET devices for improved voltage detection, AC loss-driven active quench protection, and remnant magnetization reduction in HTS magnets are also discussed.

Исследование влияния термической обработки на структуру и механические свойства полуфабрикатов из сплава NbTa(Zr,Hf,Y), предназначенных для изготовления Nb3Sn сверхпроводников

The influence of the degree of deformation and annealing on the mechanical properties of Nb-based alloy samples of different compositions: Nb-Ta-Zr, Nb-Ta-Hf, Nb-Ta-Zr-Y used in the manufacture of Nb3Sn superconductors is studied. The deformability of Nb-based alloys in the composition of single-fiber composite Nb3Sn superconductors, which were manufactured using the technology of an internal tin source and the «powder – in – tube» method, has been studied. It is shown that the values of the time resistance of samples with a sheath made of Nb alloys 7.5 wt.% Ta–0.5 wt.% Zr and Nb–7.5 wt.% Ta–1 wt. % Zr are at the same level of ~ 650 MPa, and the elongation values are ~ 2%. The structural features of the fracture surface of Nb-based alloy samples with varying degrees of accumulated deformation and single-fiber conductors have been studied. The results of the work will be used in the development of technological modes for manufacturing Nb3Sn-based superconductors.

Correlating critical current density, quench protection, relaxation time and entropy in superconductors after disturbances—Intermediate summary

<p>This paper summarizes results recently obtained from simulation of transient temperature excursions in filamentary and thin film superconductors. Under multi-component heat transfer in the complicated conductor cross sections and materials composition of present High Temperature Superconductors, numerical, Finite Element and Monte Carlo simulations are applied to solve Fourier’s differential equation with high spatial and temporal resolution. The overall aim was to encircle the quench problem in superconductors and to provide new stability criteria from correlations between superconductor critical current density, density of electron pairs, and relaxation time and entropy. Relaxation, correlation and entropy analysis presented in this paper extends the spectrum of standard methods to avoid quench to a new tool. As results, quench starts always locally, and as a highlight of this investigation, a second “critical” temperature, <em>T<sub>Quench</sub></em>, has been identified that with high probability exists below standard critical temperature. Entropy is the driving force for relaxation of the superconductor to new equilibrium after a disturbance.<strong></strong></p>

Study on the electro-magneto-mechanical characteristics of CORC superconducting cable with striations

CORC superconducting cable is a compact and flexible composite superconductor. It is widely used in large power systems because of its good flexibility and high engineering current density. In these applications, reducing the AC loss generated by the superconductor is a key factor in studying the electromagnetic field of the superconducting conductor, which affects the operational stability of the entire superconducting power device. Currently, the use of striated tape-wound cables not only allows for flexible wiring at design time but also effectively reduces AC losses. This technology has been widely used in large superconducting magnet equipment. In this paper, the finite element model of single superconducting tape and CORC superconducting cable is established based on the finite element idea. The electromagnetic properties and mechanical changes are numerically calculated by H-method. The results show that both the current density and the magnetic field of a single superconducting tape show a gradual penetration from the two sides to the center. The area of maximum current density and magnetic field distribution is at the tape boundary. The distribution of current density, magnetic field and Lorentz force of three-dimensional CORC superconducting cable is similar. All of them are gradually attenuated from the maximum value at the boundary to the center position. It is worth noting that the current density, magnetic field and Lorentz force of the striated superconducting cables are smaller than the values without striations. The calculation results of the finite element model in this paper show that the striations weaken the current density, magnetic field and Lorentz force of the CORC superconducting cable by about 8.77%, 16.21% and 9.23%. Moreover, the presence of striations can effectively reduce the AC loss of superconductors.

Самопроизвольное вращение магнитов, левитирующих над высокотемпературным сверхпроводником

Levitation of a cylindrical permanent magnet over a high-temperature superconductor cooled by liquid nitrogen can be accompanied by spontaneous oscillations and rotation. The reason for spontaneous rotation of the magnet is magnetization inhomogeneity induced by the temperature gradient. An experiment was carried out on the levitation of Nd–Fe–B magnets over a composite high-temperature superconductor. The experimental results confirm that the rotation frequency depends on the difference in the magnetization values in its upper and lower halves of the magnet. Methods for controlling the rotation frequency of a levitating magnet are proposed.

Studying the effect partial Ni2O3 nano-particles compensation on the properties of the compound Bi2Sr2-xYxCa2Cu3-yNiyO10+δ superconductors

Partial compensation Ni2O3 nanoparticles have been considered in relation to their effects on the structure, electric, morphology, and composition of Bi-2223. X-ray diffraction was used to quantify structural characteristics, and the results showed that all of the crystals in the samples are orthorhombic, with the ratio at which the Bi-2223 phase develops increasing The constancy of the lattice along the c-axis was observed. The trend that has been observed suggests that there is a direct proportionality between the concentration of Ni2O3 and the magnitude of the increase. Suggestive of a high-temperature superconductor (Bi2Sr2-xYxCa2Cu3-yNiyO10+δ) composition, where y=0=0.03=0.12 Thanks to 3D AFM, the morphology of the surface has been thoroughly studied. The test specimens showed good crystalline structure and a smooth, uniform surface. We measured Tc with 4 separate probes. The maximum temperature constant (Tc) was measured to be 143 K at y=0.12.

Synthesis and Characterization of 15N‐Labeled Poly(sulfur nitride) in Bulk and in Superconductor Composites

Abstract15N‐labeled tetrasulfur tetranitride (S415N4) was synthesized by reacting S2Cl2 with 15NH3. The reaction was finalized with 14NH3. The successful labeling was confirmed by solution 15N nuclear magnetic resonance (NMR) spectroscopy. S415N4 was used for the synthesis of poly(sulfur nitride) S15Nx via the intermediate species of S2N2. It was a topochemical polymerization in the solid state. The isotope ratio in the labeled polymer was obtained by laser deposition ionization time‐of‐flight mass spectroscopy. Solid‐state 15N NMR spectroscopy of S15Nx indicates that at least three different chemical environments for 15N atoms are present in the crystals. Finally, SNx was polymerized in the presence of two other superconductors, MgB2 and yttrium barium copper oxide (YBCO), which demonstrates the capability of SNx for grain boundary engineering.

Effect of nano ZrO2 addition on the properties of Ca0.86Sr0.14CuO2 added Bi 2223 composites

Effect of introducing nano ZrO2 particles into (Ca,Sr)CuO2 added Bi 2223 superconductor composites is studied. Microstructures revealed that 20 mol. % (Ca,Sr)CuO2 phase added to Bi 2223 formed as micron sized particles among the Bi 2223 platelet shaped grains. Distribution of (Ca,Sr)CuO2 in Bi 2223 has enhanced the critical current density (Jc) and flux pinning force density (Fp ) substantially to fields up to 9 T at 20 K. Introduction of nano ZrO2 into the composite reacted with (Ca,Sr)CuO2 particles and formed additional secondary phases of increasing amount with a rise in ZrO2 content. This resulted in lowering of Jc(0) due to a gradual reduction in the fraction of superconducting phases, but retained the enhanced field range in which flux pinning was achieved. At 10 wt.% addition of ZrO2, Bi 2223 phase was suppressed, and Bi 2212 phase was promoted. Scaling behaviour of pinning force density has shown the dominant mechanism at low fields to be normal surface pinning due to interfacial defects. The fact that (Ca,Sr)CuO2 distributes itself as fine spherical particles in Bi 2223, without causing degradation of the superconducting matrix material, is of significance and opens up a scope to optimize the microstructures further for enhancement of flux pinning.

Deep Generative Model for Inverse Design of High-Temperature Superconductor Compositions with Predicted Tc > 77 K.

Identifying new superconductors with high transition temperatures (Tc > 77 K) is a major goal in modern condensed matter physics. The inverse design of high Tc superconductors relies heavily on an effective representation of the superconductor hyperspace due to the underlying complexity involving many-body physics, doping chemistry and materials, and defect structures. In this study, we propose a deep generative model that combines two widely used machine learning algorithms, namely, the variational auto-encoder (VAE) and the generative adversarial network (GAN), to systematically generate unknown superconductors under the given high Tc condition. After training, we successfully identified the distribution of the representative hyperspace of superconductors with different Tc, in which many superconductor constituent elements were found adjacent to each other with their neighbors in the periodic table. Equipped with the conditional distribution of Tc, our deep generative model predicted hundreds of superconductors with Tc > 77 K, as predicted by the published Tc prediction models in the literature. For the copper-based superconductors, our results reproduced the variation in Tc as a function of the Cu concentration and predicted an optimal Tc = 129.4 K, when the Cu concentration reached 2.41 in Hg0.37Ba1.73Ca1.18Cu2.41O6.93Tl0.69. We expect that such an inverse design model and comprehensive list of potential high Tc superconductors would greatly facilitate future research activities in superconductors.

Исследование микротвердости композиционных материалов высокотемпературный сверхпроводник YBCO—нановолокна MoO3

В работе исследованы сверхпроводящие поликристаллические композиты YBa2Cu3O7-x + MoO3 с содержанием нановолокон MoO3 1, 5, 10, 15% (мас.). Из измерений электрического сопротивления определены температура и ширина перехода в сверхпроводящее состояние образцов с описанием вероятных механизмов наблюдаемых изменений. Из измерений микротвердости по Виккерсу определены модуль упругости, предел текучести, вязкость разрушения и индекс хрупкости. При исследованиях физико-механических свойств объемных образцов ВТСП содержащих MoO3, для интерпретации данных микроиндентирования и объяснения результатов с учетом эффекта размера вдавливания было использовано пять различных моделей.

Effects of cobalt nanoparticles addition in Cu0.5Tl0.5-1223 superconductor composite

Effects of cobalt nanoparticles addition in Cu0.5Tl0.5-1223 superconductor composite

Lightweight, highly tough and durable YBa2Cu3O7 -x superconductor.

The inherent brittleness and low sustainability of YBa2Cu3O7 -x (YBCO) bulk superconductor seriously impede its wide applications. It is a great challenge to achieve toughening of this material and maintain its invariable superconductivity at the same time. Here, we fabricate bulk YBCO composite superconductor with a density of 2.15g cm-3, which consists of interlocking dual network construction and shows high toughness and durability. The results show that its unit normalized fracture energy at 77K reaches 638.6 kN m-2, which is ∼14.8 times that of YBCO bulk prepared by the top-seeded melt textured growth (TSMTG) method. Its critical current shows no degradation during the toughening process. Moreover, after 10 000 cycles, the sample does not fracture with the decay of critical current at 4K of 14.6% whereas the TSMTG sample fractures only after 25 cycles.

Study of superconducting gap in presence of antiferromagnetism in iron pnictide superconductors

A Hamiltonian model of the pnictide composite superconductors is presented to study the Superconducting(SC) gap. The total Hamiltonian has been solved by writing equations of motion for single particle Greens function of Zubarev type. Equations for appropriate single particle correlation functions are derived and the order parameters corresponding to superconductivity and antiferromagnetism are determined. The equations for superconducting gap and antiferromagnetic gap are solved self-consistently and numerically. The multi-gap superconductivity is studied for different values of interlayer coupling constant parameters and Debye frequencies.

Structural and electrical investigations of novel CdFeO/(Bi,Pb)-2212 superconductor composite

ABSTRACT The current investigation reports the influence of the addition of CdFeO nanoparticles on the structural and superconducting properties of the (Bi,Pb)-2212 phase. The formation of an orthorhombic phase of Bi-2212 superconductor is confirmed by the X-ray powder diffraction measurements. The scanning electron microscope measurements show an improvement in the grain connectivity and a decline of voids due to the CdFeO nanoparticles addition. The Fourier transform infra-red spectroscopy is used to associate the absorption bands to equivalent functional groups. The DC-electrical resistivity and the I-V characteristic measurements show an enhancement of the superconducting transition temperature (Tc ) and the critical current density (Jc ) up to 0.02 wt% addition of CdFeO, respectively. The elemental composition and oxidation states are determined using X-ray photoelectron emission spectroscopy. The results suggest a correlation between the electric behavior and the cationic equilibrium reactions among Pb2+ ions in Bi3+ or Cu2+ sites.

Bulk NdNiO2 is thermodynamically unstable with respect to decomposition while hydrogenation reduces the instability and transforms it from metal to insulator

Through CaH2 chemical reduction of a parent R3+Ni3+O3 perovskite form, superconductivity was recently achieved in Sr-doped NdNiO2 on SrTiO3 substrate. Using density functional theory (DFT) calculations, we find that stoichiometric NdNiO2 is significantly unstable with respect to decomposition into 1/2[Nd2O3 + NiO + Ni] with exothermic decomposition energy of +176 meV/atom, a considerably higher instability than that for common ternary oxides. This poses the question if the stoichiometric NdNiO2 nickelate compound used extensively to model the electronic band structure of Ni-based oxide analog to cuprates and found to be metallic is the right model for this purpose. To examine this, we study via DFT the role of the common H impurity expected to be present in the process of chemical reduction needed to obtain NdNiO2. We find that H can be incorporated exothermically, i.e., spontaneously in NdNiO2, even from H2 gas. In the concentrated limit, such impurities can result in the formation of a hydride compound NdNiO2H, which has significantly reduced instability relative to hydrogen-free NdNiO2. Interestingly, the hydrogenated form has a similar lattice constant as the pure form (leading to comparable XRD patterns), but unlike the metallic character of NdNiO2, the hydrogenated form is predicted to be a wide gap insulator thus, requiring doping to create a metallic or superconducting state, just like cuprates, but unlike unhydrogenated nickelates. While it is possible that hydrogen would be eventually desorbed, the calculation suggests that pristine NdNiO2 is hydrogen-stabilized. One must exercise caution with theories predicting new physics in pristine stoichiometric NdNiO2 as it might be an unrealizable compound. Experimental examination of the composition of real NdNiO2 superconductors and the effect of hydrogen on the superconductivity is called for.

Elastic Properties of a Sc-Zr-Nb-Ta-Rh-Pd High-Entropy Alloy Superconductor

We report the elastic properties of the hexanary high-entropy alloy superconductor (ScZrNbTa)$_{0.685}$[RhPd]$_{0.315}$ ($T_c\approx7$ K), by Resonant Ultrasound Spectroscopy experiments. The derived elastic constants are bulk modulus $K=132.7$ GPa, Young's modulus $E=121.0$ GPa, shear modulus $G=44.9$ GPa, and Poisson's ratio $\nu$=0.348 for room temperature. The Young's and shear moduli are $\sim 10\%$ larger than those in NbTi/Cu composite superconductor with similar $T_c$, while the ductility is comparable. Moreover, the mechanical performance is further enhanced at cryogenic temperature. Our work confirms the advantageous mechanical properties of high-entropy alloy superconductors and suggests the application prospects.

The Debye temperatures of the constituents of a composite superconductor

Born and Karman had pointed out a long time ago that a composite anisotropic solid must be characterized by multiple Debye temperatures (DTs). Since all non-elemental superconductors (SCs) are similar materials, we deal here with the problem of resolving the DT of a composite SC– usually given as single value --- into the DTs of its constituents. These DTs are a primary requirement for the application of the generalized BCS equations which have been shown to shed light on several properties of not only the high-Tc SCs, but also a variety of others such as SrTiO3 and the so-called exotic Fe-based heavy-fermion SCs which have been a serious concern for theoreticians for a long time. The SCs dealt with here are MgB2, YBCO, Tl-2212 and Bi-2212.

Design and research of magnetically levitated testbed with composite superconductor bearing for micro thrust measurement

A high temperature superconducting (HTS) magnetically levitated testbed has been developed for the steady thrust measurement of miniature ion electrospray thruster. The structure of the testbed mainly consists of an HTS composite bearing, a magnetic shielding plate, an active electromagnetic brake and a laser displacement sensor. The steady thrust is described as a function of the equilibrium angle displacement of the floating frame. Furthermore, the mechanical behaviors of HTS composite bearing were studied via finite element simulation and experiments, which include the load capacity, levitation stiffness and background noise. The results show that the thrust testbed can keep in low noise and have a load capacity up to 4 kg. According to the ignition testing of the electrospray thruster, the thrust force of 25.2 was measured by the testbed, which is close to the design value of miniature ion electrospray thruster.

Calculation, design and manufacture of heteropolar magnetic levitation and linear drive systems of maglev transport

Background: The methods of calculation and elements of the technology for creating heteropolar magnetic systems of levitation, lateral stabilization and a rotor-runner of a traction linear synchronous motor for the development of the transport technology "Russian Maglev" in order to achieve an increased levitation gap of 0.2 m, reduce the threshold speed of the exit vehicle in levitation mode up to 10 km/h.
 Aim: to develop methods for calculating and designing heteropolar poles from elementary permanent magnets, coils of the same type based on composite low-temperature superconductors and high-temperature tape superconductors of the second generation and a step-by-step technology for their production.
 Tasks:
 
 Creation of an on-board magnetic system of levitation and lateral stabilization, allowing to provide a levitation gap of 0.2 m, a threshold value of vehicle speed of 10 km/h when transition to levitation mode, to reduce stray magnetic fields to the level of the natural field of terrestrial magnetism of 50 T;
 Creation of a rotor-runner of a linear synchronous motor with an ironless stator with a power of 10 MW.
 
 Methods: outlines the main calculation methodologies: "analysis" and "synthesis". The "analysis" methodology is adopted in solving the "direct" calculation problem, when the configuration of the magnetic system is set and the magnetic field in the working area is calculated, and, if necessary, the stray magnetic fields. This methodology can be effectively applied if there is experience in creating magnetic systems. Otherwise, the "synthesis" methodology is applied, which is used in solving the "inverse" calculation problem, in which the picture of the distribution of the magnetic field in the working zone is set and the configuration of the magnetic system is found (synthesized).
 Results of the study performed:
 
 The parameters and characteristics of high-energy permanent magnets made of rare-earth metals, low-temperature and high-temperature superconducting winding materials have been analyzed, the choice of permanent magnets and superconducting winding material has been made;
 Calculations of the magnetic system of permanent magnets in the "Halbach assembly" and in the traditional assembly in a toothed ferromagnetic core have been carried out;
 Calculations of a track coil with a rectangular cross-section of the winding are performed;
 Methods for calculating and optimizing superconducting magnetic systems from a set of similar track modules have been developed;
 
 Conclusions: The results of the performed fundamental research will allow starting the calculation, design and construction of conveyor-main passenger and freight lines of maglev transport, as well as urban public transport.