Properties Of MgB2 Research Articles

Effect of proton fluence on the superconducting properties of MgB2. irradiated with protons of high energy

Effects of proton irradiation on the superconducting properties of sintered MgB2 samples were investigated as a function of proton fluence at fixed energy. All experimental data suggest that critical current densities, irreversibility field and creep activation energy are enhanced because of the complex disorder, which mainly affects the grain boundaries, brought on the crystalline structure by the energetic protons.

First-principles investigation of the superconducting properties of MgXB4 (X = Al, Li, Na, K)

The discovery of superconductivity of MgB2 has attracted considerable research attention. Further exploration and discovery of MgB2-like superconductors are important to determine the properties of MgB2 and enhance our understanding of the superconducting mechanism. Four MgB2-like MgXB4 (X = Al, Li, Na, K) superconductors based on an MgB2 structure were designed in this study. The electronic structure, phonon dispersion relationship, Eliashberg spectral function, electron-phonon coupling constant (λ), and superconductivity of MgXB4 were investigated using a first-principles approach. The results indicated that MgXB4 (X = Al, Li, Na, K) were dynamically stable and demonstrated metallic characteristics. Further study of the Eliashberg spectral function and electron-phonon coupling constant indicated that these compounds were superconductors. The calculated superconducting transition temperatures (TC) of MgXB4 (X = Al, Li, Na, K) were 0.12, 22.7, 28.1, and 30.4 K, respectively.

Nb sheathed MgB2 superconducting tape with addition of VB2

MgB2 superconductor is a strategic material for practical applications, due to its superconducting properties as well as the low cost of the raw materials. For many technological applications cable, wire or tape format are required. The addition of VB2 in the MgB2 superconducting bulk had already been used in previous works as an efficient method to enhance the critical current density of the MgB2. In the present work, MgB2 superconducting tapes were developed and characterized using different amount of VB2 addition. Niobium was used as sheath material. The goal of this work is to create an efficient method to improve the transport properties of MgB2 superconducting tapes to be useful for practical application. The results include microstructural, crystallographic, magnetic and transport characterizations. All analyzes were performed together to study the influence of the VB2 addition on the superconducting behavior of MgB2 tapes.

Enhancement of Jc in C6H16N2 added MgB2 superconductor without carbon substitution for boron

The influence of C6H16N2 addition on the microstructural and superconducting properties of MgB2 was systematically investigated. Unlike previously reported carbon sources, the C6H16N2 additive had no effect on the lattice parameters of MgB2. However, the obvious improvement of critical current density (Jc) was obtained for C6H16N2 added MgB2 without carbon substitution for boron. The average grain size was reduced with the addition of C6H16N2. Additionally, different numbers of spherical MgB2 grains appeared inside the C6H16N2 added MgB2. As the added amount of C6H16N2 increased, the active cross-sectional area fraction (AF) values first increased then decreased. The possible reasons for these results have been discussed. The additive C6H16N2 resulted in a small depression in Tc and slightly increased the ΔTc of MgB2 at 0 T. The Hc2 (T) and Hirr (T) values of C6H16N2 added MgB2 samples are larger than those of pure MgB2 at temperatures below 25 K. It was concluded that the reduced grain size and the improved grain connectivity were mainly correlated with the enhancement of the Jc, Fp, Hc2, and Hirr performances in C6H16N2 added MgB2 superconductors.

Improved superconducting properties in graphene-doped MgB2 bulks prepared by high energy ball milling

MgB2 bulks with graphene doping were synthesized by high energy ball milling process. The effect of high energy ball milling and graphene doping on the microstructure and critical current density of MgB2 was studied systematically. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and physical property measurement system (PPMS), respectively. The densities of ball-milled graphene-doped samples were larger than those of pure samples. The superconducting properties of MgB2 could be increased by the high energy ball milling process, in comparison with the sample prepared by grinding process. Moreover, the significant improvement of superconducting properties for ball-milled MgB2 samples could be achieved with the addition of graphene. The combination of graphene doping and suitable ball milling could refine the grain and improve the inter-grain connectivity of MgB2. MgB2 with 3 at% graphene doping prepared by high energy ball milling with 2 h exhibited very high critical current density of 6.4 × 105 A/cm2 at 20 K and 0 T.

Research Progress of Electromagnetic Properties of MgB2 Induced by Carbon-Containing Materials Addition and Process Techniques

For the high transition temperature (Tc) and low cost taking both raw materials and fabrication process into account, MgB2 has been a competitive candidate to replace the conventional NiTi superconductor for high-temperature application in fault current limiters, transformers, motors, magnetic resonance imaging, adiabatic demagnetization refrigerators, generators, etc. The carbon-containing materials addition induced high critical current density (Jc) is reviewed based on their influences on the upper critical field (Hc2), flux pinning force, and connectivity. The doping effects were compared in the overview focusing on SiC, organic dopants, and graphene-related dopants. SiC doping is featured for the high-field critical current density, which is caused by the increased Hc2 attributed to the substitution of carbon on boron site and the strong flux pinning force offered by the nanosized secondary phases in the MgB2 matrix. Organic dopants have the advantage over SiC dopant for their relatively homogeneous distribution in the MgB2 matrix based on wet mixing of the organics and the raw boron powders. Low doping level of two-dimensional materials can improve the superconducting properties in all measured fields because of the combined advantages of carbon substitution effect and grain connectivity. MgB2 fabricated with carbon-encapsulated boron also introduces strong flux pinning centers in MgB2, which show weak destruction of the connectivity of the MgB2 grains as reflected by the low-magnetic-supercurrent behavior. High-pressure treatment and diffusion method can fabricate high-density MgB2 superconductors with better connectivity and increase the Jc compared with the in situ and ex situ methods.

Influence of milling energy of in-situ precursor powder on the properties of Ti-doped MgB2

The effect of Ti-doping on the electrical properties of MgB2 bulks was studied in dependence on the milling energy of the used in-situ precursor powder. Ti-powder was added to a mixture of Mg- and B-powder before milling in three different concentrations related to the atomic weight of Mg (Mg1-xTixB2 with x = 0.025/0.05/0.1). From each doping concentration two different powders were milled with a planetary ball mill (for 1 resp. 10 h, rotation speed 250 rpm). This corresponds to a milling energy of 5⋅108 J/kg resp. 5⋅109 J/kg. The electrical resistivity in normal state of the bulk samples is increasing by Ti-doping. The most interesting point is the influence of Ti-doping on the magnetic field dependence of the critical current density jc of samples prepared with powders milled with different energy. A remarkable increase of jc was found with increasing Ti-content at 4.2 K and external fields higher than around 4 T for the powder with lower milling energy. Not any effect could be measured at the powder milled with higher energy. If we take into account that the grain sizes of the samples prepared with higher energy milled powder is remarkably smaller than that of the other sample it can be noticed that Ti-doping has only a distinct effect on the grain size, like discussed in [1], of samples with coarser powder, not on high energy milled powders.

Design and characterisation of ex situ bulk MgB2 superconductors containing a nanoscale dispersion of artificial pinning centres

MgB2 pellets containing a nanoscale dispersion of artificial pinning centres have been successfully manufactured through a powder metallurgy route based on the oxide dispersion strengthened (ODS) concept more usually used for steels and superalloys. Commercial MgB2 powder and Y2O3 nano-powder were mechanically alloyed in a high energy planetary ball mill and consolidated using the field assisted sintering technique. The composite powders were ball milled for different times up to 12 h and characterised by means of particle size analysis, x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure and superconducting properties were characterised by density, XRD, STEM and magnetic property measurements. The powder microstructure comprised Y2O3 particles dissolved into the MgB2 matrix. After consolidation there was a near-uniform dispersion of precipitated YB4 and MgO particles. A bulk 0.5 wt% Y2O3-MgB2 composite showed the best superconducting performance with a significant improvement in J c at high field compared with unmodified MgB2, and only a small reduction in T c . The results suggest that the ODS concept is promising to improve the superconducting properties of MgB2.

Aluminum Ion Implantation in MgB2 Thin Films

Superconducting magnesium diboride is a possible candidate for replacing Nb in superconducting radio frequency (SRF) cavities because of its higher T c and potentially higher breakdown field. However, the existence of two energy gaps, the σ gap at 7.2 eV and the π gap at 2.2 eV, could impact the RF properties of MgB 2 . It has been shown that chemical doping and disorder can increase the interband scattering, thus modifying the two gaps. In this work, we performed Al ion implantation in MgB 2 thin films to introduce Al doping in the films. The Al ion implanted films showed decreases in transition temperature, from 40.4 K in the pristine films to non-superconducting above the dose of 2 × 10 14 atoms/cm 2 . An expansion in the c-axis lattice parameter with increasing dose was also observed. These results suggest that the degradation of superconductivity in the Al ion implanted films is mainly due to the ion beam damage rather than Al doping.

Excitation Test of Solenoid MgB2 Coil Under External Magnetic Field Immersed in Liquid Hydrogen

We have been developing a liquid hydrogen (LH2) cooled superconducting energy apparatus, such as superconducting generator, SMES, and so on. An MgB2 superconductor whose critical temperature is 39 K is now developing for a practical use. It can be cooled by LH2 with a sufficient temperature margin. An MgB2 wire is expected to be used for superconducting equipment due to the low production cost and material cost. In order to design equipment using the MgB2 wire, we have carried out measurement tests of critical superconducting properties of MgB2 under LH2 cooling and investigation of heat transfer characteristics of LH2. There are few reports on the experimental results of a superconducting coil using a long MgB2 wire under the LH2 immersion cooling. In this study, we have carried out an excitation test of a small MgB2 coil immersed in LH2 under an external magnetic field. Tanaka et al. proposed that the test coil is a 529 turn solenoid coil with an inner diameter of 120 mm, an outer diameter of 190 mm, and a height of 41 mm, which was produced by the Wind and React method using a 300-m multifilament MgB2 wire (Hitachi Ltd., Ibaraki, Japan). The temperature of LH2 was changed from 21 K to 30 K and the external magnetic field was also applied up to 4.5 T. In the experiment, the critical characteristic of the solenoid coil was measured and a coil load line was obtained.

Comparative study of hot and cold press and their effect on superconducting properties of coronene added bulk MgB2

In this study, the superconducting properties of 4 wt% coronene (C24H12) added polycrystalline bulk MgB2 samples prepared by hot pressing and cold pressing, were reported in detail. The results were compared to determine one of which pressing methods is more useful to substitute of carbon released from C24H12 into MgB2 structure and to increase the superconducting properties of MgB2. The lattice strain, crystallite size, residual resistivity, superconducting transition temperature (Tc), critical current density (Jc), flux pinning force density (Fp) and vertical/lateral levitation force (Fz, Fx) were analysed for the hot and cold pressed samples. The a-lattice parameter and Tc value reduced sharply for 4 wt% C24H12 added cold pressed sample, resulting in a notable decrease of increment ratio of Jc and Fp values, while the depressing of Tc is lower for 4 wt% C24H12 added hot pressed sample. The cold pressing strongly increased the lattice strain, confirming more C substitution, while the hot pressing ensured smaller crystallite size. The Jc and Fp values were respectively found as 4.6 × 103 A/cm2, 1.3 × 104 A/cm2, 5.8 × 103 A/cm2 and 1.8 × 108 N/m3, 5.1 × 108 N/m3, 2.3 × 108 N/m3 for the pure sample and, 4 wt% C24H12 added hot and cold pressed samples at 20 K, 4 T. The maximum repulsive and attractive levitation force values at 20 K in ZFC and FC regimes were obtained for the 4 wt% C24H12 added hot pressed sample. Finally, the hot pressing provides an effective way to substitute C into MgB2 lattice without a remarkable decrease of Tc value, ensuring more homogenous and compacted structure, more electron–phonon interaction and strong flux pinning force.

The effect of milling conditions on the magnetic and topological properties of MgB2 synthesized by high-energy ball mill and sintered at low temperature

Magnesium diboride, MgB2, is known to be an important high-temperature superconductor material. High-energy ball milling with subsequent low-temperature sintering remains an attractive solid-state method for its synthesis. One main optimization parameter of this method is to ensure a balance between cold welding and fracturing at the milling stages. Therefore, in many cases, the use of a process control agent at the milling stage is considered to be the preferred solution in the prevention of particle size enlargement. The aim of this paper is to determine the effect of dry and toluene-assisted milling on the magnetic and surface topology properties of obtained MgB2. The calculated critical current density of 2.89 × 105 A/cm2 at 10 K 0.3 T for a toluene-assisted sample, compared with the 2.37 × 105 A/cm2 for a dry-milled sample as well as the relatively higher mean surface roughness, clearly indicated a notable positive contribution of surfactant use on the true alloying of MgB2 by mechanical activation.

Control of superconductivity in MgB2 by ion bombardment

The superconducting properties of MgB2 can be modified via controlled introduction of lattice defects by ion bombardment. Here, magnetometry and Raman spectroscopy are used to study ∼160 nm-thick MgB2 films bombarded at room temperature with megaelectronvolt-energy He, Ar, or Xe ions. Ion bombardment leads to a monotonic reduction in the critical superconducting transition temperature, transition width, and critical current density. There is a clear collision cascade density effect, whereby radiation-induced changes, once normalized to the number of atomic displacements generated, are greater for heavier ions. The sharpening of the superconducting transition with increasing ion dose suggests improved homogeneity of irradiated films. The suppression of superconducting properties correlates with the growth of defect signatures revealed by Raman spectroscopy. Superconducting properties can be recovered by annealing at relatively low temperatures of 500 °C, even for films exposed to high doses of heavy ions. These results have direct implications for the performance of MgB2 in radiation environments and understanding its defect-mediated superconductivity.

Ab Initio Study of the Electronic, Vibrational, and Mechanical Properties of the Magnesium Diboride Monolayer

Magnesium diboride gained significant interest in the materials science community after the discovery of its superconductivity, with an unusually high critical temperature of 39 K. Many aspects of the electronic properties and superconductivity of bulk MgB 2 and thin sheets of MgB 2 have been determined; however, a single layer of MgB 2 has not yet been fully theoretically investigated. Here, we present a detailed study of the structural, electronic, vibrational, and elastic properties of monolayer MgB 2 , based on ab initio methods. First-principles calculations reveal the importance of reduction of dimensionality on the properties of MgB 2 and thoroughly describe the properties of this novel 2D material. The presence of a negative Poisson ratio, higher density of states at the Fermi level, and a good dynamic stability under strain make the MgB 2 monolayer a prominent material, both for fundamental research and application studies.

Study of Superconducting, Structural, and Thermal Properties of SnO2 Added MgB2 Bulks.

A series of SnO2 added MgB2 bulk superconductors were prepared by in situ route to study the effect of oxygen doping on superconducting and structural properties of MgB2. Several (MgB2)1-x (SnO2) x samples were fabricated with x ranging from 0, 3 wt%, 4 wt%, and 6 wt%. Upper critical field (B C2) and irreversible field (B irr) were measured by physical property measurement system. Thermal analysis was performed on the as-received SnO2 powder. Critical current densities (J cm ) were obtained at 4.2 K using magnetic measurement. X-ray diffraction results showed evidence of full SnO2 decomposition in all the doped bulk samples and a shift of a-axis in MgB2 lattice was seen. Oxygen was successfully released during heat treatment, yet no enhancement of B C2 or B irr was seen, indicating that oxygen atoms did not end up in the host lattice. Further exploration of different processing procedures is still needed in order to get oxygen substitution on the host lattice sites.

Preparation of MgB2 superconducting wires by the rapid heating and quenching method

In order to reduce the long-term annealing process and prevent excessive grain growth, we attempted to fabricate MgB2 superconducting wires by the rapid heating and quenching (RHQ) method. In this paper, we have successfully prepared MgB2 superconductive wires with self-made RHQ equipment, and the effect of various Joule heating currents on the properties of MgB2 was investigated. The XRD results showed that the sample had relatively strongest diffraction peaks and least heterogenous peaks when the loading heating current was 350 A, so the superconducting transition temperature (Tc) could reach 38.5 K. Because the MgB2 phase particles were small and uniformly distributed, there was a good critical current density (Jc). That is, in the self-field, the Jc value of the 350 A sample reached up to 1.39 × 105 A/cm2, and the downward trend was the flattest. When the magnetic field was 7 T, the critical current density was still as high as 300 A/cm2.

Enhancement of superconducting parameters of MgB2 by low energy carbon ion implantation

The aim of work is to study the effects of carbon ion implantation on enhancement of superconducting properties of MgB2. Pure MgB2 bulk samples are irradiated by carbon ion beam of energy 40 keV (beam current 1 µA) at different fluences. After irradiation, there is enhancement in superconducting properties viz., critical current density (Jc), critical magnetic field (Hc2), comparing to pristine sample. Estimated with Ginzburg-Landau theory method at zero kelvin, the critical magnetic field Hc2(0) for irradiated sample shows an increase of 47 T than that of 38 T reported for pristine sample. There is also a four times increase in Jc after implantation. Improvement in grain connectivity with ion fluence is found in surface morphological studies. Raman spectroscopic studies show a shift in resonance peak related with E2g phonon modes after irradiation. This shifting is caused due to improvement in scattering and alteration of Fermi surface in implanted samples. These results are explained in correlation with the lattice disorder.

Effect of malonic acid and of different doping methods on the superconducting properties of MgB2 superconductors

In this paper, malonic acid was tested as a new carbon source and its effects on the structural and superconducting properties of bulk MgB2 have been systematically investigated. The detailed pyrolysis process of malonic acid was analyzed to understand the possible doping mechanism of malonic acid added MgB2 samples. The weight fraction of MgO phase and the actual carbon substitution level in bulk MgB2 increased with a higher amount of malonic acid addition, which was proven to be mainly caused by the reaction of Mg and CO2 gas. A moderate amount of malonic acid addition resulted in grain refinement and enhanced flux pinning. Bulk MgB2 with 10 wt% malonic acid addition showed much higher Jc values in the entire magnetic field range. Three different doping methods with the same amount of malonic acid addition were compared. MgB2 samples using malonic acid and ethanol processed boron showed the highest Jc value, which was 7.2 times larger than that of the pure MgB2 at 20 K and 5 T.

Preparation and Properties of MgB2 Thin Films

The superconducting transition temperature of 140 nm ± 10 nm thin films on sapphire substrates, which were deposited by magnetron sputtering, was around 36 K. Using a magnetization technique, the film's critical current density was estimated as J C = 1.8 × 107 А/cm2 at 10 K, J C = 8 × 106 А/m 2 at 20 K in a zero magnetic field B, and J C = 3 × 106 А/m2 at 10 K and B = 5 T. The values of the upper critical magnetic field B c2 and the irreversibility field B irr estimated using the four-probe technique were B C2(22 K) = 15 T when H||film surface, 11 T when H⊥film surface, and B irr(22 K) = 11 T when H||film surface. The X-ray study showed that the microstructure of the film contains only MgB2 and MgO (in minority). The SEM and EPXMA study and quantitative Auger spectroscopy analysis revealed periodical variations of the film composition on the nanolevel and the presence of (mainly) two intercalated Mg-B-O-C phases of slightly different, especially in oxygen content, and thus with different conductivity and, possibly, with different T C. The characteristics of superconducting magnesium diboride films make them promising for application in electronic devices, e.g., as high-pass filters.

Improved transport properties of MgB2 superconducting round wires via minute addition of gold nanoparticles

This study investigates the effect of gold nanoparticles (Au-NPs) on structural, morphological, electrical and magnetic properties of Fe/MgB2 wires 1.00 mm in diameter. Au-NPs were obtained by pulsed laser ablation of gold in acetone and mixed with Mg+ 2B powder mixture for in-situ powder-in-tube wire making process. Resulting drawn wires were subjected to inert atmosphere heat treatments at different temperatures. Transport measurements were performed on 1.00 mm round wires samples in a closed cycle cryostat under magnetic fields perpendicular to wire axis.