Wafer-Scale MgB2 Superconducting Devices.

Progress in superconducting device and detector technologies over the past decade has realized practical applications in quantum computers, detectors for far-infrared telescopes, and optical communications. Superconducting thin-film materials, however, have remained largely unchanged, with aluminum still being the material of choice for superconducting qubits and niobium compounds for high-frequency/high kinetic inductance devices. Magnesium diboride (MgB2), known for its highest transition temperature (Tc = 39 K) among metallic superconductors, is a viable material for elevated temperature and higher frequency superconducting devices moving toward THz frequencies. However, difficulty in synthesizing wafer-scale thin films has prevented implementation of MgB2 devices into the application base of superconducting electronics. Here, we report ultrasmooth (<0.5 nm root-mean-square roughness) and uniform MgB2 thin (<100 nm) films over 100 mm in diameter and present prototype devices fabricated with these films demonstrating key superconducting properties including an internal quality factor over 104 at 4.5 K and high tunable kinetic inductance in the order of tens of pH/sq in a 40 nm thick film. This advancement will enable development of elevated temperature, high-frequency superconducting quantum circuits, and devices.

A study on properties of electroless Ni-B/MgB2 coatings on AZ91 magnesium alloy.

This study explores MgB2 as a reinforcing agent in electroless deposition on AZ91 magnesium alloy substrates, evaluating its impact on coating properties. X-ray diffraction (XRD) analysis shows that the amorphous Ni-B coating masks initial magnesium peaks, while MgB2 enhances MgB2O(OH)6, MgB2O5, MgO, and MgB2xOy oxide phases. SEM images illustrate morphological shifts from cauliflower-like Ni-B structures to dendritic and fibrous MgB2 forms, with higher MgB2 concentrations leading to granular structures with randomly oriented crystallites resembling platelets, indicating increased magnesium content. MgB2-reinforced Ni-B coatings exhibited higher hardness than the substrate but lower than as-deposited Ni-B. Friction coefficients initially decreased with Ni-B, increased significantly with 0.1 g MgB2, and decreased with higher reinforcements, remaining higher than substrate and as-deposited Ni-B. MgB2 reinforcement increased surface roughness, causing local agglomerations in 0.5 g MgB2 coatings. Contact angle measurements demonstrated enhanced hydrophilicity due to MgB2's superhydrophilic properties influenced by surface roughness. Antibacterial tests revealed superior properties with 0.1 g MgB2, suggesting a transition to MgB2-enriched structures and influencing material properties. While Ni-B/MgB2 coatings improved over substrate, further research is needed to optimize parameters and understand stabilizer effects. These coatings also exhibited superhydrophilicity and promising antibacterial properties, suggesting potential in advanced surface engineering applications.

Sandwich-Structured Nanofiber Dressings Containing MgB2 and Metformin Hydrochloride With ROS Scavenging and Antibacterial Properties for Wound Healing in Diabetic Infections.

The treatment of chronic diabetic wounds is a major challenge due to oxidative stress, persistent hyperglycemia, and susceptibility to bacterial infection. In this study, multifunctional sandwich-structured nanofiber dressings (SNDs) are prepared via electrospinning. The SNDs consisted of an outer layer of hydrophobic polylactic acid (PLA) fibers encapsulating MgB2 nanosheets (MgB2 NSs), a middle layer of PLA and polyvinylpyrrolidone (PVP) fibers encapsulating the MgB2 NSs and metformin hydrochloride complex (MgB2-Met), and an inner layer of water-soluble PVP fibers encapsulating MgB2-Met. Because of their special sandwich structure, SNDs have high photothermal conversion efficiency (24.13%) and photothermal cycle performance. SNDs also exhibit a photothermal effect, bacteria-targeting effect of MgB2, electrostatic attraction ability of metformin hydrochloride (Met), and strong antibacterial activity against Escherichia coli (E. coli) and methicillin-resistant Staphylococcus aureus (MRSA). SNDs can eliminate intracellular reactive oxygen species (ROS) by regulating the hydrogen release from MgB2. In addition, SNDs have good biocompatibility, can effectively inhibit the inflammatory factor Interleukin-6 (IL-6), and promote granulation tissue formation, collagen deposition, and diabetic wound healing. These findings offer a promising approach for clinical treatment of diabetic wounds.

Ion Current Rectification Activity Induced by Boron Hydride Nanosheets to Enhance Magnesium Analgesia.

The limited analgesic efficiency of magnesium restricts its application in pain management. Here, we report boron hydride (BH) with ion currents rectification activity that can enhance the analgesic efficiency of magnesium without the risks of drug tolerance or addiction. We synthesize MgB2, comprising hexagonal boron sheets alternating with Mg2+. In pathological environment, Mg2+ is exchanged by H+, forming two-dimensional borophene-analogue BH sheets. BH interacts with the charged cations via cation-pi interaction, leading to dynamic modulation of sodium and potassium ion currents around neurons. Additionally, released Mg2+ competes Ca2+ to inhibit its influx and neuronal excitation. In vitro cultured dorsal root neurons show a remarkable increase in threshold potential from the normal -35.9 mV to -5.9 mV after the addition of MgB2, indicating potent analgesic effect. In three typical pain models, including CFA-induced inflammatory pain, CINP- or CCI-induced neuropathic pain, MgB2 exhibits analgesic efficiency approximately 2.23, 3.20, and 2.0 times higher than clinical MgSO4, respectively, and even about 1.04, 1.66, and 1.95 times higher than morphine, respectively. The development of magnesium based intermetallic compounds holds promise in addressing the non-opioid medical need for pain relief.

The Influence of Electroluminescent Inhomogeneous Phase Addition on Enhancing MgB2 Superconducting Performance and Magnetic Flux Pinning.

As a highly regarded superconducting material with a concise layered structure, MgB2 has attracted significant scientific attention and holds vast potential for applications. However, its limited current-carrying capacity under high magnetic fields has greatly hindered its practical use. To address this issue, we have enhanced the superconducting performance of MgB2 by incorporating inhomogeneous phase nanostructures of p-n junctions with electroluminescent properties. Through temperature-dependent measurements of magnetization, electronic specific heat, and Hall coefficient under various magnetic fields, we have confirmed the crucial role of inhomogeneous phase electroluminescent nanostructures in improving the properties of MgB2. Experimental results demonstrate that the introduction of electroluminescent inhomogeneous phases effectively enhances the superconducting performance of MgB2. Moreover, by controlling the size of the electroluminescent inhomogeneous phases and optimizing grain connectivity, density, and microstructural uniformity, we can further improve the critical temperature (TC) and flux-pinning capability of MgB2 superconducting materials. Comprehensive studies on the physical properties of MgB2 superconducting structures added with p-n junction electroluminescent inhomogeneous phases also confirm the general effectiveness of electroluminescent inhomogeneous phases in enhancing the performance of superconducting materials.

Investigation of Layered Structure Formation in MgB2 Wires Produced by the Internal Mg Coating Process under Low and High Isostatic Pressures.

Currently, MgB2 wires made by the powder-in-tube (PIT) method are most often used in the construction and design of superconducting devices. In this work, we investigated the impact of heat treatment under both low and high isostatic pressures on the formation of a layered structure in PIT MgB2 wires manufactured using the Mg coating method. The microstructure, chemical composition, and density of the obtained superconductive wires were investigated using scanning electron microscopy (SEM) with an energy-dispersive X-ray spectroscopy (EDS) analyzer and optical microscopy with Kameram CMOS software (version 2.11.5.6). Transport measurements of critical parameters were made by using the Physical Property Measurement System (PPMS) for 100 mA and 19 Hz in a perpendicular magnetic field. We observed that the Mg coating method can significantly reduce the reactions of B with the Fe sheath. Moreover, the shape, uniformity, and continuity of the layered structure (cracks, gaps) depend on the homogeneity of the B layer before the synthesis reaction. Additionally, the formation of a layered structure depends on the annealing temperature (for Mg in the liquid or solid-state), isostatic pressure, type of boron, and density of layer B before the synthesis reaction.

Comparison of the Field Trapping Ability of MgB2 and Hybrid Disc-Shaped Layouts.

Superconductors have revolutionized magnet technology, surpassing the limitations of traditional coils and permanent magnets. This work experimentally investigates the field-trapping ability of a MgB2 disc at various temperatures and proposes new hybrid (MgB2-soft iron) configurations using a numerical approach based on the vector potential (A→) formulation. The experimental characterization consists in measurements of trapped magnetic flux density carried out using cryogenic Hall probes located at different radial positions over the MgB2 sample, after a field cooling (FC) process and the subsequent removal of the applied field. Measurements were performed also as a function of the distance from the disc surface. The numerical modelling of the superconductor required the evaluation of the critical current density dependence on the magnetic flux density (Jc(B)) obtained through an iterative procedure whose output were successfully validated by the comparison between experimental and computed data. The numerical model, upgraded to also describe the in-field behavior of ARMCO soft iron, was then employed to predict the field-trapping ability of hybrid layouts of different shapes. The most promising results were achieved by assuming a hollow superconducting disc filled with a ferromagnetic (FM) cylinder. With such a geometry, optimizing the radius of the FM cylinder while the external dimensions of the superconducting disc are kept unchanged, an improvement of more than 30% is predicted with respect to the full superconducting disc, assuming a working temperature of 20 K.

Inhibiting Mg Diffusion and Evaporation by Forming Mg-Rich Reservoir at Grain Boundaries Improves the Thermal Stability of N-Type Mg3 Sb2 Thermoelectrics.

N-type Mg3 Sb2 -based thermoelectric materials show great promise in power generation due to their mechanical robustness, low cost of Mg, and high figure of merit (ZT) over a wide range of temperatures. However, their poor thermal stability hinders their practical applications. Here, MgB2 is introduced to improve the thermal stability of n-type Mg3 Sb2 . Enabled by MgB2 decomposition, extra Mg can be released into the matrix for Mg compensation thermodynamically, and secondary phases of Mg─B compounds can kinetically prevent Mg diffusion along grain boundaries. These synergetic effects inhibit the formation of Mg vacancies at elevated temperatures, thereby enhancing the thermal stability of n-type Mg3 Sb2 . Consequently, the Mg3.05 (Sb0.75 Bi0.25 )1.99 Te0.01 (MgB2 )0.03 sample exhibits negligible variation in thermoelectric performance during the 120-hour continuous measurement at 673 K. Moreover, the ZT of n-type Mg3 Sb2 can be maintained by adding MgB2 , reaching a high average ZT of ≈1.1 within 300-723 K. An eight-pair Mg3 Sb2 -GeTe-based thermoelectric device is also fabricated, achieving an energy conversion efficiency of ≈5.7% at a temperature difference of 438 K with good thermal stability. This work paves a new way to enhance the long-term thermal stability of n-type Mg3 Sb2 -based alloys and other thermoelectrics for practical applications.

CRITICAL CURRENT DENSITIES AND N-VALUES OF MGB2 CONDUCTORS FOR SMES, MRI, AND LOW AC LOSS APPLICATIONS.

Multifilamentary MgB2 strands (filament numbers 36 to 114) prepared by the in-situ power-in-tube (PIT) route with carbon doping contents of 0, 2, and 3.2% were wound on barrels for transport Jc and n-value measurement at 4.2 K in fields of up to 12 T. The strand and gauge lengths were 1 m and 0.5 m. Heat treatments at 675 °C and 650 °C centered around the melting point of Mg (650 °C) and both utilized the liquid-solid reaction. A pair of strands, with and without 2% C doping exhibited the Jc (B) crossover effect. Studied were the dependencies of Jc on field strength, dopant concentration, and cabling and the dependence of n-value on field strength.

Superconducting In Situ/Post In Situ MgB2 Joints.

The superconducting joints of superconducting in situ MgB2 wires have been of great interest since the first MgB2 wires were manufactured. The necessity of joining fully reacted wires in applications such as NMR brings complexity to the methodology of connecting already reacted wires sintered under optimised conditions via a mixture of Mg + 2B and subsequential second heat treatment to establish fully superconducting MgB2 joints. Some of the data in the literature resolved such a procedure by applying high cold pressure and sintering at a low temperature. A topical review publication did not address in depth the question of whether cold sintering is a potential solution, suggesting that hot pressing is the way forward. In this paper, we discuss the potential joint interfacial requirements, suggesting a thermo-mechanical procedure to successfully form a superconductive connection of two in situ reacted wires in the presence of Mg + 2B flux. The critical current at 25 K of the researched junction achieved 50% Ic for an individual in situ wire.

Effect of Low Annealing Temperature on the Critical-Current Density of 2% C-Doped MgB2 Wires Used in Superconducting Coils with the Wind-and-React (W&R) Method-High-Field and High-Temperature Pinning Centers.

The use of a low annealing temperature during the production of coils made from superconducting materials is very important because it reduces the production costs. In this study, the morphology, transport critical-current density (Jc), irreversible magnetic field (Birr), and critical temperature (Tc) of straight wires and small 2% C-doped MgB2 coils were investigated. The coils were made using the wind-and-react (W&R) method and annealed at various temperatures from 610 °C to 650 °C for 2-12 h. Critical-current measurements were made for both the coils and straight wires at the temperatures of 4.2 K, 20 K, 25 K, and 30 K. During our research study, we determined the process window that provides the best critical parameters of the coils (annealing at a temperature of 650 °C for 6 h). Moreover, we observed that small coils made with unreacted MgB2 wire and then annealed had morphology and critical parameters similar to those of straight 2% C-doped MgB2 wires. Moreover, small-diameter bending of 20 mm and 10 mm did not lead to transverse cracks, which can cause a large reduction in Jc in the coils. This indicates that the processes of optimization of thermal treatment parameters can be carried out on straight MgB2 wires for MgB2 superconducting coils.

Fabrication of Ru loaded MgB2 with guar gum hybrid for photocatalytic degradation of crystal violet.

Today, dyes/pigment-based materials are confronting a serious issue in harming marine ecology. Annihilate these serious water pollutants using photoactive 2D nanohybrid catalysts showed promising comparativeness over available photocatalysts. In the present work, a facile route to decorate Ruthenium (Ru) on 2D MgB2 flower-like nanostructures was developed via ecofriendly guar gum biopolymer substantial template (MgB2/GG@Ru NFS) and its photocatalytic performance was reported. Synthesis of MgB2@Ru, MgB2/GG@Ru NFS and commercial MgB2, was studied by FTIR, XRD, FE-SEM, EDX, AFM, TEM, UV-vis spectra, and XPS analysis. From the results, the MgB2/GG@Ru NFS exhibited a superior photocatalytic performance (99.7 %) than its precursors MgB2@Ru (79.7 %), and MgB2 (53.7 %), with the degradation efficiency of the crystal violet (CV) within 100 min under visible light irradiation. The proposed photo-catalyst MgB2/GG@Ru NFS showed negligible loss of photocatalytic activity even after five successive cycles, revealing its reusability and enhanced stability due to the network structure. The photocatalytic mechanism for MgB2/GG@Ru NFS was evaluated by trapping experiment of active species, verifying that superoxide (O2-) and electron (e-) contributed significant role in the dye degradation.

Boron-based magnesium diboride nanosheets preparation and tested for antimicrobial properties for PES membrane.

Antimicrobial resistance to antibiotics for current bacterial infection treatments is a medical problem. 2D nanoparticles, which can be used as both antibiotic carriers and direct antibacterial agents due to their large surface areas and direct contact with the cell membrane, are important alternatives in solving this problem. This study focuses on the effects of a new generation borophene derivative obtained from MgB2 particles on the antimicrobial activity of polyethersulfone membranes. MgB2 nanosheets were created by mechanically separating magnesium diboride (MgB2) particles into layers. The samples were microstructurally characterized using SEM, HR-TEM, and XRD methods. MgB2 nanosheets were screened for various biological activities such as antioxidant, DNA nuclease, antimicrobial, microbial cell viability inhibition, and antibiofilm activities. The antioxidant activity of nanosheets was 75.24 ± 4.15% at 200 mg/L. Plasmid DNA was entirely degraded at 125 and 250 mg/L nanosheet concentrations. MgB2 nanosheets exhibited a potential antimicrobial effect against tested strains. The cell viability inhibitory effect of the MgB2 nanosheets was 99.7 ± 5.78%, 99.89 ± 6.02%, and 100 ± 5.84% at 12.5 mg/L, 25 mg/L, and 50 mg/L, respectively. The antibiofilm activity of MgB2 nanosheets against S. aureus and P. aeruginosa was observed to be satisfactory. Furthermore, a polyethersulfone (PES) membrane was prepared by blending MgB2 nanosheets from 0.5 wt to 2.0 wt %. Pristine PES membrane also has shown the lowest steady-state fluxes at 30.1 ± 2.1 and 56.6 L/m2h for BSA and E. coli, respectively. With the increase of MgB2 nanosheets amount from 0.5 to 2.0 wt%, steady-state fluxes increased from 32.3 ± 2.5 to 42.0 ± 1.0 and from 15.6 ± 0.7 to 24.1 ± 0.8 L/m2h, respectively for BSA and E. coli. E. coli elimination performance of PES membrane coated with MgB2 nanosheets at different rates and the membrane filtration procedure was obtained from 96% to 100%. The results depicted that BSA and E. coli rejection efficiencies of MgB2 nanosheets blended PES membranes increased when compared to pristine PES membranes.

The Influence of Preparation Temperature on the Different Facets of Bulk MgB2 Superconductors.

Two MgB2 samples were prepared using the spark plasma sintering (SPS) technique at different temperatures-950 °C (S1) and 975 °C (S2)-for 2 h under 50 MPa pressure to study the influence of preparation temperature on different facets, namely those perpendicular (PeF) and parallel (PaF) to the compression direction of uniaxial pressure during the SPS of MgB2 samples. We analyzed the superconducting properties of the PeF and PaF of two MgB2 samples prepared at different temperatures from the curves of the critical temperature (TC), the curves of critical current density (JC), the microstructures of MgB2 samples, and the crystal size from SEM. The values of the onset of the critical transition temperature, Tc,onset, were around 37.5 K and the transition widths were about 1 K, which indicates that the two samples exhibit good crystallinity and homogeneity. The PeF of the SPSed samples exhibited slightly higher JC compared with that of the PaF of the SPSed samples over the whole magnetic field. The values of the pinning force related to parameters h0 and Kn of the PeF were lower than those of the PaF, except for Kn of the PeF of S1, which means that the PeF has a stronger GBP than the PaF. In low field, the most outstanding performance was S1-PeF, whose critical current density (JC) was 503 kA/cm2 self-field at 10 K, and its crystal size was the smallest (0.24 µm) among all the tested samples, which is consistent with the theory that a smaller crystal size can improve the JC of MgB2. However, in high field, S2-PeF had the highest JC value, which is related to the pinning mechanism and can be explained by grain boundary pinning (GBP). With an increase in preparation temperature, S2 showed a slightly stronger anisotropy of properties. In addition, with an increase in temperature, point pinning becomes stronger to form effective pinning centers, leading to a higher JC.

Progress on the Fabrication of Superconducting Wires and Tapes via Hot Isostatic Pressing.

Fabrication of high-performance superconducting wires and tapes is essential for large-scale applications of superconducting materials. The powder-in-tube (PIT) method involves a series of cold processes and heat treatments and has been widely used for fabricating BSCCO, MgB2, and iron-based superconducting wires. The densification of the superconducting core is limited by traditional heat treatment under atmospheric pressure. The low density of the superconducting core and a large number of pores and cracks are the main factors limiting the current-carrying performance of PIT wires. Therefore, to improve the transport critical current density of the wires, it is essential to densify the superconducting core and eliminate pores and cracks to enhance grain connectivity. Hot isostatic pressing (HIP) sintering was employed to improve the mass density of superconducting wires and tapes. In this paper, we review the development and application of the HIP process in the manufacturing of BSCCO, MgB2, and iron-based superconducting wires and tapes. The development of HIP parameters and the performance of different wires and tapes are reviewed. Finally, we discuss the advantages and prospects of the HIP process for the fabrication of superconducting wires and tapes.

Role of Superconducting Materials in the Endeavor to Stop Climate Change and Reach Sustainable Development.

Progress in the mass production of newly developed bulk (Gd0.33Y0.13Er0.53)Ba2Cu3Oy "(Gd,Y,Er)123" and MgB2 systems is presented. Two batches of (Gd,Y,Er)123 pellets of 20 mm diameter and 7 mm thick were prepared in air by an infiltration growth "IG" process. Trapped field distribution profiles of fully grown bulk samples clearly showed that all samples were single-grain and the trapped field values were more than 0.5 T at 77 K, 1.3 mm above top surface. The best bulk exhibited the trapped field value of 0.63 T at 77 K. Ultra-sonication technique was employed for refining precursors of both (Gd,Y,Er)211 and boron. TEM studies revealed that boron powder subjected to ultrasonication was refined up to nanoscale. The micron-sized particles were reduced to nanoscale, which led to improvement of critical current by up to 36% in bulk MgB2 at 20 K and self-field. This progress in fabrication of high-performance LREBa2Cu3Oy and MgB2 superconducting bulks further promotes commercialization of superconductors' production as a mode of sustainable technology.

High Critical Current Density of Nanostructured MgB2 Bulk Superconductor Densified by Spark Plasma Sintering.

In situ MgB2 superconducting samples were prepared by using the spark plasma sintering method. The density of the obtained bulks was up to 95% of the theoretical value predicted for the material. The structural and microstructural characterizations of the samples were investigated using X-ray diffraction and SEM and correlated to their superconducting properties, in particular their critical current densities, Jc, which was measured at 20 K. Extremely high critical current densities of up to 6.75 × 105 A/cm2 in the self-field and above 104 A/cm2 at 4 T were measured at 20 K, indicating that vortex pinning is very strong. This property is mainly attributed to the sample density and MgB2 nanograins in connection to the presence of MgO precipitates and areas rich in boron.

High Critical Current Density in the Textured Nanofiber Structure in Multifilament MgB2 Wires Made by the Powder-In-Tube (PIT) Technique.

We show that the structure of multifilament MgB2 wires made by the powder-in-tube (PIT) method can be texturized by annealing the structure under high isostatic pressure. Our results show that we obtained continuous fibers with a uniform diameter of 250 nm in all 36 filaments, a small grain size of approximately 50 nm and a high density of the superconducting material. These results contribute to a significant improvement in the critical current density in high magnetic fields, e.g., 100 A/mm2 at 14 T and 4.2 K.

Ignition and Combustion Characteristic of B·Mg Alloy Powders.

Boron and its alloys have been explored a lot and it is expected that they can replace pure aluminum powder in the energetic formulation of active materials. MgB2 compounds were prepared and characterized by a combination of mechanical alloying and heat treatment. The ignition and combustion of boron-magnesium alloys were studied with the ignition wire method and laser ignition infrared temperature measurement. The results show that MgB2 has good ignition characteristics with maximum ignition temperatures obtained by the two various methods of 1292 K and 1293 K, respectively. Compared with boron, the ignition temperature of MgB2 is greatly reduced after alloying. The ignition reaction of MgB2 mainly occurs on the surface and the ignition process has two stages. In the initial stage of ignition, the large flame morphology and combustion state are close to the combustion with gaseous Mg, whereas the subsequent combustion process is close to the combustion process of B. Compared with boron, the ignition temperature of MgB2 is greatly reduced which suggests that MgB2 may be used in gunpowder, propellant, explosives, and pyrotechnics due to its improved ignition performance.

Modelling and Performance Analysis of MgB2 and Hybrid Magnetic Shields.

Superconductors are strategic materials for the fabrication of magnetic shields, and within this class, MgB2 has been proven to be a very promising option. However, a successful approach to produce devices with high shielding ability also requires the availability of suitable simulation tools guiding the optimization process. In this paper, we report on a 3D numerical model based on a vector potential (A)-formulation, exploited to investigate the properties of superconducting (SC) shielding structures with cylindrical symmetry and an aspect ratio of height to diameter approaching one. To this aim, we first explored the viability of this model by solving a benchmark problem and comparing the computation outputs with those obtained with the most used approach based on the H-formulation. This comparison evidenced the full agreement of the computation outcomes as well as the much better performance of the model based on the A-formulation in terms of computation time. Relying on this result, the latter model was exploited to predict the shielding properties of open and single capped MgB2 tubes with and without the superimposition of a ferromagnetic (FM) shield. This investigation highlighted that the addition of the FM shell is very efficient in increasing the shielding factors of the SC screen when the applied magnetic field is tilted with respect to the shield axis. This effect is already significant at low tilt angles and allows compensating the strong decrease in the shielding ability that affects the short tubular SC screens when the external field is applied out of their axis.