Bulk Superconductors Research Articles

High performance one-step grown half-moon shaped YBCO bulk superconductors

High-temperature superconducting (HTS) undulator exploiting the high trapped field of HTS bulk superconductors enables the design of extremely short-period insertion devices for synchrotron light sources and free electron lasers. In such a promising application the trapped field performance and the uniformity of the HTS bulk superconductors are essential. In this study, the half-moon shaped YBa2Cu3O7−δ (YBCO) single-grain superconductors have been directly grown by the top-seeded melted-growth method. Half-moon shaped samples directly grown from preforms with four different type of seed crystal arrangements were compared with that cut from larger cylindrical bulk superconductors in regarding to the trapped magnetic fields and correspondingly the distribution. We found that the arrangement of seed crystals greatly affects the melt-growth process and hence the homogeneity of the samples. The one-step grown half-moon shaped samples show higher trapped field (B trap), 0.542 T for a 24 mm and 0.785 T for a 32 mm diameter sample, and better uniformity of trapped field distribution compared to that obtained from machining with B trap of 0.427 T and 0.528 T. It was found that the growth sectors would be restricted when the seed crystal was placed at the edge of a preform, and the angle of the seed crystal, parallel or 45° to the long edge would influence the melt growth as well.

Superconductivity in pressurized trilayer La4Ni3O10-δ single crystals.

The pursuit of discovering new high-temperature superconductors that diverge from the copper-based model1-3 has profound implications for explaining mechanisms behind superconductivity and may also enable new applications4-8. Here our investigation shows that the application of pressure effectively suppresses the spin-charge order in trilayer nickelate La4Ni3O10-δ single crystals, leading to the emergence of superconductivity with a maximum critical temperature (Tc) of around 30 K at 69.0 GPa. The d.c. susceptibility measurements confirm a substantial diamagnetic response below Tc, indicating the presence of bulk superconductivity with a volume fraction exceeding 80%. In the normal state, we observe a strange metal behaviour, characterized by a linear temperature-dependent resistance extending up to 300 K. Furthermore, the layer-dependent superconductivity observed hints at a unique interlayer coupling mechanism specific to nickelates, setting them apart from cuprates in this regard. Our findings provide crucial insights into the fundamental mechanisms underpinning superconductivity, while also introducing a new material platform to explore the intricate interplay between the spin-charge order, flat band structures, interlayer coupling, strange metal behaviour and high-temperature superconductivity.

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Synthesis, magnetic and superconducting properties of high-entropy rare-earth boride (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)(Rh,Ru)4B4

We report the structure and physical properties of a new rare-earth (RE) high-entropy boride (HEB) (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)(Rh0.85Ru0.15)4B4. The as-cast HEB consists of a highly crystallized, body-centered-tetragonal phase (I41/acd, a = 7.460 Å and c = 14.860 Å); here, all the RE elements share the same crystallographic site and are distributed uniformly on both macroscopic and microscopic scales. At high temperature, the HEB shows a paramagnetic behavior with a large effective moment peff yet it becomes a bulk superconductor upon cooling below 6.0 K. Remarkably, a peculiar cocktail effect of properties is observed: while the lattice parameters, Tc and peff of the HEB agree reasonably well with the compositional averages of the individual pseudo-ternary counterparts, the increased RE mixing entropy tends to suppress the superconductivity even without the magnetic exchange interactions, and a reentrant resistive transition is induced at magnetic fields above 0.8 T. Our results indicate that the high-entropy design of the RE sublattice is a viable way to tune the electrical and magnetic properties in RE intermetallics.

High field HTS electromagnet with direct-current supplied bulk superconductors: old dream turns into reality?

High field HTS electromagnet with direct-current supplied bulk superconductors: old dream turns into reality?

A Novel Method to Enhance the Content and size of Y-211 Particles in YBCO bulk Superconductors Grown by RE+011 TSIG Process

A Novel Method to Enhance the Content and size of Y-211 Particles in YBCO bulk Superconductors Grown by RE+011 TSIG Process

Superconductivity in Nb5Ir3N: a nitrogen-filled electride

The hexagonal Mn5Si3-type compounds possess the capability to accommodate specific atoms in the interstices, thereby creating filled Mn5Si3-type structures. In Nb-based Mn5Si3-type system, interstitial atoms like carbon (C) or oxygen (O) have been identified to induce or enhance superconductivity. However, the compounds filled with nitrogen (N) are scarce, and the existence of a N-filled superconductor remains unknown. Here, we report the discovery of a novel ternary nitride superconductor, Nb5Ir3N, synthesized via incorporating N into the electride Nb5Ir3. The crystal structure of Nb5Ir3N conforms to the filled Mn5Si3-type, belonging to the P63/mcm space group (No. 193), with cell parameters a = b = 7.8398(2) Å and c = 5.1108(1) Å. Electrical resistivity and magnetic susceptibility demonstrate that Nb5Ir3N is a type-II superconductor with a T c of 8.7 K. The estimated lower and upper critical fields are 11.0 mT and 12.16 T, respectively. Moreover, specific heat measurements confirm the bulk superconductivity with enhanced electron–phonon coupling in Nb5Ir3N, as demonstrated by the normalized specific heat jump ΔC e/γT c ∼ 1.59. First-principles calculations emphasize the strong spin–orbit coupling in Nb5Ir3N.

A route to fabricate low resistance joints between Eu–Ba–Cu–O bulk, single grain superconductors

The fabrication of large (RE)–Ba–Cu–O single grains [(RE)BCO], where RE = Y, Gd, Eu or Sm, with the complex geometries required for many practical applications is currently limited by the time intensive, complex nature of the grain growth process. In addition, the shapes achievable using established melt processing techniques, such as top seeded melt growth, are constrained significantly by the limited number of post-processing techniques readily available. Machining of these materials is also difficult given their ceramic-like mechanical properties, which makes them both brittle and hard. A potential alternative to the slow and inflexible melt growth processes is to join many small, single grains to form one large composite grain, connected by electrically and mechanically high-performance joints. A reliable joining technique would also greatly reduce the need for post-growth machining processes. In this work we extend our previous investigation of the use of single grain YBCO-Ag as an intermediate joining material to achieve effective and reliable superconducting joints between EuBCO-Ag bulk, single grain superconductors. The technique reported in the earlier studies requires limited specialist equipment and does not require tight process parameter control, since there is no need to re-grow the joining material at the intergrain interface. This technique is of particular interest given that the difference between the peritectic temperatures of the bulk superconductor and the intermediate joining material is large. We report the properties of seven joints engineered at different joining temperatures. The trapped field properties of the resulting joined samples were measured and the microstructure at the position of the joint examined. We demonstrate that this simple and the rapid joining technique makes it possible to manufacture composite grains in an industrially important (RE)BCO bulk superconductor with comparable superconducting properties to those of a single grain of similar dimensions.

Axial Stiffness Augmentation by Adding Superconductor Bulks or Limiting Permanent Magnet Rings to a Horizontal Axis Zero-Field Cooled High-Tc Radial Passive Superconducting Bearing

This paper analyzes the viability of different solutions to passively augment the axial stiffness of a horizontal axis radial levitation passive magnetic bearing (PMB) with a previously studied topology. The zero-field cooling (ZFC) of high-temperature superconductor (HTS) bulks promotes higher magnetic impulsion and levitation forces and lower electromagnetic losses than those with field-cooling (FC) but, on the other hand, the guiding stability is much lower than those with FC. Because of stability reasons, FC was adopted in most superconducting maglev systems. The trend of this research group has been to develop a horizontal axis HTS ZFC radial levitation PMB presenting notable levitation forces with reduced electromagnetic losses, defined by a topology that creates guiding stability. Previous work has shown that optimizing the bearing geometry to maximize magnetic guidance forces might not be enough to guarantee the axial stiffness required for many applications. First, the extent to which guidance forces are augmented by increasing the number of HTS bulks in the stator is evaluated. Then, the axial stiffness augmentation by passively adding two limiting permanent magnet (PM) rings is evaluated. The results show that the axial stiffness is highly augmented by adding limiting PM rings with no significant additional investment. This change enables the use of the studied ZFC superconducting PMB in high-precision axial stability applications, such as precision gyroscopes, horizontal axis propellers, and turbines.

Improving the screening ability of high-temperature superconductors by combining disk-shaped bulks and closed-loop coated conductors

In this work, we demonstrate experimentally the remarkable DC magnetic screening ability of hybrid superconducting screens. The configurations under investigation combine a 30 mm-diameter disk-shaped superconducting bulk, or another with a 10 mm-diameter hole, with different closed superconducting loops made from coated conductors. The loops are placed coaxially with the bulk. The bulk superconductors and the closed-loop coated conductors are made of GdBa2Cu3O7 and the experiments are performed in liquid nitrogen (77 K). The DC and inhomogeneous field to be screened is produced by a bespoke coil and reaches around 100 mT at the location of the superconducting bulk, which is much less than its full-penetration field. By mapping the magnitude of the flux density using a 3-axis cryogenic Hall probe, we show that such a hybrid superconducting screen allows the maximum shielding factor SF above the bulk to be almost doubled. For the best investigated hybrid configuration, the SF reaches ∼45 at 2.7 mm above the bulk. In addition, the area of the spatial region for which less than half of the applied field remains (SF >2 ) is roughly multiplied by 4 when compared to a situation involving only a disk-shaped bulk. In this work, this region corresponds to a 60 mm-diameter circle. The choice of the loop diameter is found to result from a trade-off between maximum SF and extension of the screened region. Finally, we detail why these hybrid configurations bring such improvements: the key point is that the flux lines generated by the source coil are diverted by the bulk towards a region where the closed-loop coated conductors can oppose the best to them.

Theoretical characterization and its application of electromagnetic anisotropy in high-temperature superconducting bulks under rotated postures

The electromagnetic anisotropy of high-temperature superconducting (HTS) bulks limits their levitation ability in the applied magnetic fields from the permanent magnet guideway (PMG), thus impeding the enhancement of load-carrying capacity in HTS pinning maglev systems. Developing a suitable matching scheme between bulk orientation and magnetic field direction is a valuable way to relieve this restriction. In this paper, a method for characterizing bulk anisotropy in a rotating coordinate system is proposed to explore the best bulk orientation. The method is based on the concept of equivalent resistivity tensor and its eigenvectors, and includes an extended description of two types of anisotropy: conductivity anisotropy and magnetic field angle dependence. It provides a theoretical foundation for simulating anisotropic bulks under any rotated posture. Experimental investigations on the levitation force distribution of cylindrical bulks with different c-axis orientation were conducted, through which the accuracy of the characterization method and calculated results were validated. Analysis of current distribution reveals that aligning the c-axis parallel to the external magnetic field helps achieve the best match between the bulk and the PMG. Additionally, considering that the two types of anisotropy have opposite effects on levitation force distribution trends, prioritizing conductivity anisotropy when analyzing anisotropic bulk is recommended. This research not only offers a theoretical framework for simulating the anisotropy of rotated HTS bulks but also provides guidance for matching the optimal bulk orientation in applied magnetic fields.

The levitation force and stiffness enhancement of single domain GdBCO bulk superconductor by an axial background magnetic field

How to improve the levitation force (FL) and its stiffness between a permanent magnet and a REBCO bulk superconductor is one of the most key and attractive problems to be solved for practical applications. In this paper, we provided a novel hybrid magnet added superconductor system (HMS) to enhance the levitation force and the stiffness, the HMS sample is assembled by a single domain GdBCO bulk with an attached permanent magnet (PM) serving as an axial background magnetic field. The results indicate that (1) the FL increased first and decreased then with the increase of the PM diameter (dPM), the largest FL is achieved when the dPM approaches the diameter of the GdBCO bulk, FL has been improved up to 152% with a thinner PM; (2) the FL increased with the increase of the PM thickness and saturated at a certain value, FL have been improved up to 168% with a thicker PM; (3) the stiffness of FL has been improved up to 187% and 201% with the increase of the PM diameter and thickness; (4) the FL and its stiffness enhancement dependent on the positive trapped field of the field cooled HMS samples. The results are of great significance to improve the performance and stability of maglev systems, the mechanism for enhancing the levitation force and stiffness property has been investigated in details.

Advancing processing of the ternary (Sm,Eu,Gd)Ba2Cu3O7-y superconductor via top-seeded infiltration growth

In this study, we present the fabrication of large single-domain ternary (Sm,Eu,Gd)Ba2Cu3O7-y bulk superconductor with enhanced superconducting properties using various REBa2Cu3Oy (RE-123) as a liquid source via the top-seeded infiltration growth process (TSIG) in air. We employed a 1:1 ratio of REBa2Cu3Oy (RE = Sm, Gd, Y and Er) and Ba3Cu5O8 as a liquid source for fabrication. Impressively, all the obtained bulk samples exhibited a superconducting transition temperature T(c, onset) above 94 K. However, the bulk sample fabricated using Y-123 + Ba3Cu5O8 as a liquid source demonstrated a T(c, onset) of 94.53 K, with a 40.14 % improvement in transition width (ΔTc) and at 77 K the bulk recorded a self-field critical current density (Jc) value of 44.73 kA/cm2 & 10.62 kA/cm2 at 1T resulting in a remarkable 93.08 % improvement in self-field Jc compared to the bulk sample fabricated using Er-123 + Ba3Cu5O8. Microstructural analysis using a scanning electron microscope revealed a significant reduction in the mean size of secondary (211) phase particles, a significant reduction of 38.41 % is observed for the Y-123 + Ba3Cu5O8 employed sample.

Space experiments using superconducting magnet technology

We report on a fast-track experiment on the International Space Station (ISS) with the Earth’s magnetic field, which has been recognized as a major task for a better understanding of our planet. For this purpose, YBCO bulk superconductors have been prepared, transported and stored on board the ISS. The properties of single grain superconducting bulk will be investigated before and after the ISS experiments. In parallel, the magnetic interaction between BEarth and our YBCO bulk was investigated. An external 3D Helmholtz coil cancels unwanted electromagnetic fields down to 5 μT. Highly sensitive flux-gate sensors monitored the magnetic configuration as the ceramic plate was cooled to cryogenic temperatures. Shielding and field concentration effects of the Earth’s magnetic field were observed and discussed. Thermally induced magnetic flux compression for future long-duration space missions was successfully tested, enabling future spacecraft shielding and braking functions.

Nanomechanical manipulation of superconducting charge-qubit quantum networks

We suggest a nanoelectromechanical setup and corresponding time-protocol for controlling parameters in order to demonstrate nanomechanical manipulation of superconducting charge-qubit quantum network. We illustrate it on an example reflecting important task for quantum information processing — transmission of quantum information between two charge-qubits facilitated by nanomechanics. The setup is based on terminals utilizing the AC Josephson effect between bias voltage-controlled bulk superconductors and mechanically vibrating mesoscopic superconducting grain in the regime of the Cooper pair box, controlled by the gate voltage. The described manipulation of quantum network is achieved by transduction of quantum information between charge-qubits and intentionally built nanomechanical coherent states, which facilitate its transmission between qubits. This performance is achieved using quantum entanglement between electrical and mechanical states.

Infiltration effect of Mg with different matter states in the reaction of MgB2 bulks

MgB2 superconductor bulks were fabricated using Mg and B precursors. The physical state of Mg (solid, liquid, or gas) significantly influences the final product, MgB2 bulk. In this study, the Solid-Solid, Liquid-Solid, and Gas-Solid methods were employed to fabricate MgB2 bulks. The superconducting properties and microstructure of various samples were systematically investigated. Notably, for the first time, nano-CT was utilized to comprehensively and non-destructively analyze the microstructure of MgB2 bulks, particularly the size and distribution of voids, which serve as the primary barrier affecting the superconducting properties. By examining the microstructure characteristics, the infiltration effect of Mg in different physical states during the reaction was analyzed, and a feasible reaction model was established. This research contributes to a better understanding of the reaction mechanism of MgB2, which may aid other researchers in enhancing the properties of MgB2 superconductors.

Temperature dependence of power transfer efficiency and power handling capability of wireless power transfer system using superconducting bulk coil

We developed a cryocooler system to reveal the temperature dependence of the quality (Q) factor of high-temperature superconducting (HTS) bulk coil and the power transfer efficiency (PTE) and power handling capability (PHC) of a wireless power transfer (WPT) system using the HTS bulk coil. The measured Q factors of the HTS bulk coil were 9051 at 77 K and 14 050 at 25 K. The measured PTEs and PHCs of the WPT system were 44.2% and 4.48 W at 77 K, and 50.8% and 25.2 W at 25 K.

Enhanced trapped magnetic field in bulk (Gd, Y, Er) Ba2Cu3O7-y via varied liquid sources in top-seeded infiltration growth process

The practical applications of the bulk superconductors are determined by the trapped field (TF) and its overall performance. This study aims to demonstrate the effect of various compositions of liquid sources on the trapped field performance of bulk superconductors fabricated using the Top-Seeded Infiltration Growth process (TSIG) in air. We utilized a combination of different liquid sources, Ba3Cu5O8, Yb2O3: BaCuO2: CuO (1:10:6) and ErBa2Cu3Oy + Ba3Cu5O8 (1:1) to fabricate the ternary bulk (Gd, Y, Er) Ba2Cu3O7-y (Gd, Y, Er)-123. The use of these liquid sources demonstrated a pivotal role in fabricating single-domain bulks, showcasing significant variation in the trapped field performance. Specifically, the bulk fabricated using ErBa2Cu3Oy + Ba3Cu5O8 (1:1) as a liquid source exhibited the best-trapped field performance, showcasing an improvement of 42.92 % compared to the bulk obtained using conventional Ba3Cu5O8 as the liquid source. An enhancement in the critical current density below 77 K was observed in the bulk material produced utilizing Ba3Cu5O8 as the liquid source, with a Jc (3T, 50 K) value reaching 244 kA/cm2. The flux pinning force density (Fp) was analyzed for all samples to understand the pinning mechanisms in ternary (Gd, Y, Er)-123 bulk materials. Furthermore, the maximum trapped field for a 30 mm bulk sample fabricated using a mixture of ErBa2Cu3Oy + Ba3Cu5O8 (1:1) was measured at 0.336T. These results emphasize the potential for enhancing or controlling the trapped field performance of the TSIG-processed RE-123 bulks by optimizing the liquid source according to the intended applications of the bulk.

R-z plane spatial critical current inhomogeneity-induced mechanical response of GdBCO superconducting bulks during field cooling magnetization

Benefiting from the high critical current density (J c), single-grain (RE)BCO (where RE = rare earth or Gd) bulks are capable of trapping over 17.6 T magnetic field which is crucial for the application of bulk superconductors. Nevertheless, during field cooling magnetization (FCM), the large mechanical stress induced by Lorentz forces may lead to fracture behavior in the brittle ceramic nature of (RE)BCO materials. Most previous numerical models that adopted simplified homogeneous J c had difficulty reflecting the real stress/strain situation in high temperature superconductor (HTS) bulks. Based on the proposed modified Jirsa model considering r-z plane J c inhomogeneity, we investigate the mechanical response of GdBCO bulks manufactured by top-seeded melt growth (TSMG) process. A 2D axisymmetric electromagnetic-thermal-mechanical coupled model is implemented to take into account the dependence of J c upon mechanical deformation. The simulation results show the electromagnetic-thermal-mechanical response of the r-z plane inhomogeneous J c model is lower than that obtained by the homogeneous J c model. This confirms Takahashi’s speculation (K Takahashi 2019 Supercond. Sci. Technol. 32 015007) about the mismatch between experimental data and the simulation results of homogeneous J c model, and suggests the stress levels in the bottom plane of HTS bulk are overestimated by the previous homogeneous J c model. On top of that, the overall stress level of GdBCO bulk is strongly determined by the magnitude and position of the Lorentz force load, and the stress distribution of inhomogeneous J c model is mainly concentrated in high J c regions near top surface, instead of being symmetrically distributed along the z-axis as in homogeneous J c model. The mechanical response of stainless steel reinforced GdBCO bulk was aslo simulated and analyzed. Finally, the coupling effect between the fracture strength variability caused by defects and cracks and the trapped field in GdBCO bulks with r-z plane J c inhomogeneity is further studied. This study may provide a relatively realistic mechanical response of HTS bulk during FCM, and a novel design consideration for its mechanical reinforcement.

Electromechanical behavior of a rectangular bulk superconductor with an inhomogeneous critical current density under pulsed-field magnetization

Bulk high-temperature superconductors are widely used in various superconducting devices for their high critical current density and the ability to trap large magnetic field. In some applications, bulk superconductors can be arranged in an array structure to increase the magnetic field strength. However, rectangular bulk superconductors can be arranged more compactly than commonly used cylindrical bulk superconductors. The unique shape of rectangular bulk superconductors results in different distributions of electromagnetic fields, temperature, and stress under a pulsed-field magnetization (PFM) than for cylindrical bulk superconductors. In bulk superconductors, growth sector boundaries and growth sector regions have different critical current density, resulting in an uneven critical current density. Therefore, in this study, the electromagnetic and mechanical behavior of non-uniform rectangular bulk superconductors during the PFM process is investigated. The corresponding distribution and variation in the magnetic field, current, temperature, and stress in the bulk are calculated and analyzed. The influence of rectangle aspect ratio on the electromagnetic and mechanical behavior is discussed. The calculation results show that the magnetic flux jumps occur accompanied by sudden changes in the temperature and pressure. The effect of the aspect ratio of rectangular bulk superconductors on their electromagnetic and mechanical properties is analyzed. The influence of preexisting cracks in a non-uniform rectangular bulk superconductor on the simulation results is discussed. The numerical results indicate that the presence of an edge crack exacerbates the magnetic flux jump as well as the jumps in the temperature and stress. However, a central crack has a relatively small effect on the stability of a bulk superconductor.