Pure MgB2 Research Articles

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.

Remarkable promotion of mechanical tensile strength of Mg1-xAxB2 superconductor via additions of ultra-high - ductile AZ61-alloy

Extruded Mg–(6%Al)–(1%Zn) ∼ (AZ61) alloy powder was applied as softener matter and grains sizes promoter in narrow range to replace on magnesium sites of Mg1-xAxB2 superconductor (where, x = 0.0,0.025,0.050,0.075 and 0.1 mol and A = AZ61) alloy) . Samples were synthesized via high temperature solid state reaction technique depending upon diffusion mechanism of Mg -vapor ions through added A-boron-matrix at 760 °C. Micro-structural features and grains sizes averages were estimated and monitored by both of 3D-AFM and SE-microscopy. Mechanical tensile was recording promising results with maximum tensile value of 52.3 MPa is for sample with x = 0.075 mol which is better than pure MgB2 (33.8 MPa.) by promotion ratio∼ 54.73%.

The Effect of Inhomogeneous Phase on the Critical Temperature of Smart Meta-superconductor MgB2

The critical temperature (TC) of MgB2, one of the key factors limiting its application, is highly desired to be improved. On the basis of the meta-material structure, we prepared a smart meta-superconductor structure consisting of MgB2 micro-particles and inhomogeneous phases by an ex situ process. The effect of inhomogeneous phase on the TC of smart meta-superconductor MgB2 was investigated. Results showed that the onset temperature ( $T_{\mathrm {C}}^{\text {on}}$ ) of doping samples was lower than those of pure MgB2. However, the offset temperature ( ${T}_{\mathrm {C}}^{\text {off}}$ ) of the sample doped with Y2O3:Eu3+ nanosheets with a thickness of 2 ∼ 3 nm which is much less than the coherence length of MgB2 is 1.2 K higher than that of pure MgB2. The effect of the applied electric field on the TC of the sample was also studied. Results indicated that with the increase of current, ${T}_{\mathrm {C}}^{\text {on}}$ is slightly increased in the samples doping with different inhomogeneous phases. With increasing current, the ${T}_{\mathrm {C}}^{\text {off}}$ of the samples doped with nonluminous inhomogeneous phases was decreased. However, the ${T}_{\mathrm {C}}^{\text {off}}$ of the luminescent inhomogeneous phase doping samples increased and then decreased with increasing current.

Study of activation energy and AC-susceptibility for nano-ZnO doped MgB2 superconductor in presence of varying amplitude of applied field

AC-susceptibility dependence of temperature measurements with varying applied magnetic field is studied for nano-ZnO doped MgB2 superconductors at different doping levels along with pristine material. The home-made susceptometer is used to measure the AC-susceptibility at different varying field (H ac = 0.2, 0.8, 4.0, 20.0 and 40.0 A/cm). The AC-susceptibility of the material shows the magnetic properties of that material either attracting or repelling in nature. The purpose of choosing the MgB2 superconductor is that because it has simple crystal structure with profound properties such as two band gaps. Generally, the AC-susceptibility has two parts, real and imaginary. The peak height of the imaginary part of the AC-susceptibilities is enhancing by increasing the applied field and shifted to the lower temperature. The real part of AC-susceptibility as a function of temperature under the presence of varying applied fields illustrates the minutely drop of the transition temperature, T c. All the samples were cooled down from 300 to 4 K in presence of applied field. The relaxation time is calculated using by optimum frequency (f = 98 Hz). The activation energy as a function of current density is measured with different doped and pure MgB2 samples. In addition, this activation energy as a function of current density is also determined under the effect of the applied field. The collective pinning model was adopted in order to calculate the activation energy as a function of current density. The current density is found to be increased as the activation energy increases in both the cases.

Record critical current density in bulk MgB2 using carbon-coated amorphous boron with optimum sintering conditions

We report on the synthesis and characterization of a sintered bulk MgB2 material produced at an optimized sintering temperature with a varying content of carbon-encapsulated amorphous boron. A series of MgB2 bulks was prepared with 0%, 1.5%, 2.8%, 7.3%, 12% and 16.5% of carbon-encapsulated boron. In the samples with 12% of carbon-encapsulated boron, Mg and MgB2C2 formation was observed. Tc was around 38.4 K for the pure MgB2 and decreased with increasing carbon content up to 25 K for 16.5 % of carbon-encapsulated boron. The highest Jc values of 470 kA/cm2 and 310 kA/cm2, in the self-field and 1 T, respectively, were achieved at 20 K, in the MgB2 sample with 1.5% of carbon-encapsulated boron. It proved that the optimized sintering conditions together with the appropriate amount of the carbon-coated boron were able to bring critical current performance of bulk MgB2 material up to the level necessary for real technical applications.

Structure and Properties of MgB2Bulks, Thin Films, and Wires

This paper describes the established correlations between the characteristics of MgB2-based superconducting materials and their structural features, in particular the oxygen distribution and content. As indicated by SEM and Auger analysis, a sizeable amount of oxygen is usually present in superconducting MgB2 -based materials (bulks, thin films, and wires). The matrix phase of bulk MgB2 contains rather small amounts of oxygen, but contains a high amount of dispersed inclusions or areas with compositions close to MgBO. X-ray phase analysis with Rietveld refinement (using the FullProf Suite program package) of several highly dense MgB2 -based bulk samples (with high critical current densities) showed that the superconducting phase had a composition within the range MgB1.68O0.26 and MgB1.74O0.32 instead of pure MgB2 . Besides, a small amount of a phase with MgO structure was observed in the materials by X-rays as well. The calculation of the enthalpy of formation confirms the possibility of oxygen solubility in MgB2 and shows that the formation of MgB1.75B0.25 is most favorable. The results of ab initio calculations of the electronic structure and stability of the MgB2 compounds with partial oxygen substitution for boron show that it is energetically preferable for oxygen atoms to replace boron pairwise.

Role of double doping with C and RE 2 O 3 oxides on the critical temperature and critical current of MgB 2 phase

Abstract A series of MgB2 samples doped with C, RE2O3 oxides (RE = Ce, Nd), and C and RE2O3oxides was prepared by the hot isostatic pressing method at high pressure: 1 GPa under argon gas. Based on X-ray diffraction and magnetization measurements it was found that the RE2O3 is not incorporated into MgB2. A secondary REB4 phase is present after the synthesis. No decrease in the critical temperature (Tc) is observed after the RE2O3 doping. The Tc of C and RE2O3 doped MgB2 is decreased by 3 K. The doping decreases the diamagnetic response in comparison to pure MgB2 phase. The highest critical current density (Jc) was 3.4 × 105 A/cm2 at 4.2 K and 0.5 T for the bulk material, and the irreversibility field for the Nd2O3 doped sample was located at high field at T = 30 K. The results indicate that inside grains of pinning centers increase Jc from 4.2 K to 25 K and decrease Jc at 30 K. On the other hand, pinning centers between grains (precipitate) increase Jc at 30 K and decrease Jc from 4.2 K to 25 K in the middle and high magnetic fields. Our research shows that carbon-encapsulated boron creates a point pinning centers.

The Effects of Structural, Thermal, and Magnetic Properties of Hexylbenzene-Doped MgB2 Superconductor

The effects of the amount of hexylbenzene additive (C12H18) on the structural, thermal, and magnetic properties of MgB2 superconductor are examined in this study. Pure and hexylbenzene-doped MgB2 bulk samples were produced with in situ solid-state reaction method. X-ray diffraction patterns of MgB2 doped with MgB2 and hexylbenzene at different ratios were determined to have MgB2 as the main phase and consisted of a small amount of MgO. Pure and different ratios of hexylbenzene-doped Mg and B starting powders were heat-treated by a differential scanning calorimeter between room temperature and 800 °C. It was determined from the differential scanning calorimetry curves obtained that the first exothermic peak pointed the MgB2 phase emerging with a solid–solid (Mg–B) reaction, and this temperature shifted towards the low temperatures as the hexylbenzene addition rates increased. It was observed that there was dependency to the applied field in all samples from the ac susceptibility measurements as a function of the temperature in pure and hexylbenzene-doped MgB2 superconductor materials, and shift towards the lower temperatures in Tc, superconducting transition temperature, with increasing content. It was observed that the changes occurred in in-phase (\(\chi ^{\prime })\) and out-off-phase (\(\chi ^{\prime \prime }\)) components of ac susceptibility both weakened the MgB2 phase structure of hexylbenzene content and, as a result of this, led to changes in the pinning mechanism.

Critical Temperature of Smart Meta-superconducting MgB2

Enhancing the critical temperature (T C ) is important not only to widen the practical applications but also to expand the theories of superconductivity. Inspired by the meta-material structure, we designed a smart meta-superconductor consisting of MgB2 microparticles and Y2O3/Eu3+ nanorods. In the local electric field, Y2O3/Eu3+ nanorods generate an electroluminescence (EL) that can excite MgB2 particles, thereby improving the T C by strengthening the electron–phonon interaction. An MgB2-based superconductor doped with one of four dopants of different EL intensities was prepared by an ex situ process. Results showed that the T C of MgB2 doped with 2 wt% Y2O3, which is not an EL material, is 33.1 K. However, replacing Y2O3 with Y2O3/Eu3+II, which displays a strong EL intensity, can improve the T C by 2.8 to 35.9 K, which is even higher than that of pure MgB2. The significant increment in T C results from the EL exciting effect. Apart from EL intensity, the micromorphology and degree of dispersion of the dopants also affected the T C . This smart meta-superconductor provides a new method to increase T C .

Improving magnetic properties of MgB2 bulk superconductors by synthetic engine oil treatment

The present study focuses on the effects of standby time of the MgB2 samples immersed in synthetic engine oil on the critical current density ( Jc(H)), magnetic field dependence of the pinning force density fp(b) and Tc performances of MgB2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB2 pellet samples were immersed at different standby time of 30min, 120min, 300min and 1440min in synthetic engine oil after the first heating process. Finally, MgB2 samples immersed in synthetic engine oil were sintered at 1000°C and kept for 15min in Ar atmosphere. The critical current density of all of MgB2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB2 sample because of the number of the pinning centers. The MgB2 sample immersed at 300min standby time in synthetic engine oil has the best performance compared to other samples. The Jc value for the pure sample is 2.0×103A/cm2, whereas for the MgB2 sample immersed at 300min standby time in engine oil the Jc is enhanced to 4.8×103A/cm2 at 5K and 3T. The superconducting transition temperature (Tc) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB2 superconductors. It was found that all MgB2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB2 bulk superconductors makes MgB2 samples immersed in synthetic engine oil a good candidate for industrial applications.

The Influence of Stearic Acid Addition on the Superconducting Properties of MgB2

Magnesium diboride superconductors are important materials used for practical applications around the world, due to the properties and to the low price of the precursor elements, as well as the possibility to apply the material in magnets and electronic devices, operating with cryocoolers. In the present work, a methodology to optimize the properties of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk superconductors is described. The method uses the addition of an organic carbon source (stearic acid, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">36</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), due to the homogeneous distribution of the doping material in the matrix, before final chemical reaction. The procedure was developed using high-energy ball milling to mix the precursor powders and performing heat treatment in a hot isostatic press, to improve the densification and grain connectivity. As a result, the critical current density enhanced around 600 times at 3T, when compared to the pure MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> samples produced using the same approach.

Addition effects of nanoscale NiO on microstructure and superconducting properties of MgB2

We have investigated the addition effect of NiO magnetic nanoparticles on crystal structure, microstructure as well as superconducting properties of MgB2. NiO-added MgB2 samples were prepared by the solid-state reaction method. The superconducting transition temperature (Tc) of 37.91 K was obtained for pure MgB2, and Tc was found to decrease systematically on increasing the addition level of NiO. X-ray diffraction (XRD) analysis revealed that no substitution of Ni for Mg in the lattice of MgB2 was occurred. The microstructural analysis shows that the pure MgB2 sample consists of plate shape MgB2 grains, and the grains get refined to smaller size with the addition of NiO nanoparticles. At 5 K, high values of critical current density (Jc) were obtained for small amount NiO-added MgB2 samples as compared to pure sample. The enhancement in Jc could be attributed to the refinement of MgB2 grains which leads to high density of grain boundaries in NiO-added MgB2 samples.

Analysis of the levitation force of pure and starch/polystyrene/MWCNT added bulk MgB2 superconductors using frozen image model under zero field cooling condition

The measurement of superconducting levitation force between permanent magnet and polycrystalline samples of pure and MgB2 added with starch, polystyrene (PS) and multiwall carbon nanotube (MWCNT) have been performed under zero field cooling (ZFC) condition at 20K in both descending and ascending modes. For this, the bulk pellets were synthesized by conventional solid state sintering technique. The XRD data indicate well developed MgB2 phase. However, a decrease in lattice parameter ‘a=b’ have been observed for doped MgB2 samples. Superconducting transition temperature of MgB2 also decreases with starch/PS/MWCNT addition. Unlike MWCNT, the addition of starch/polystyrene is found to enhance the levitation force of MgB2 superconductor. The levitation force between PM and investigated pellets in ZFC condition is explained well in terms of the updated version of modified frozen image model and the magnetic moment originated due to vertical motion of the superconductors have been estimated. It may be noted that except for MWCNT, addition of starch/PS in MgB2 improves the magnetic moment generated by vertical movement of pure MgB2. However, this improvement is more pronounced for 1wt.% of PS added MgB2, which indicates more flux trapping and hence better levitation properties in 1wt.% of PS added MgB2. The vertical stiffness estimated for pure and starch/PS/MWCNT doped MgB2 samples indicate that the levitation force are more sensitive in the region close to the PM.

Improving the Critical Temperature of MgB2 Superconducting Metamaterials Induced by Electroluminescence

The MgB2 superconductor was doped with electroluminescent Y2O3:Eu, to synthesise a superconducting metamaterial. The temperature dependence of the resistivity of the superconductor indicates that the critical temperature (T C) of samples decreases when increasing the amount of doped Y 2 O 3 nanorods, due to impurity (Y 2 O 3, MgO and YB 4). However, the T C of the samples increase with increasing amount of doped Y 2 O 3:Eu 3+ nanorods, which are opposite to doped Y 2 O 3 nanorods. Moreover, the transition temperature of the sample doped with 8 wt % Y 2 O 3:Eu 3+nanorods is higher than those of doped and pure MgB 2. The T C of the sample doped with 8 wt % Y 2 O 3:Eu 3+ nanorods is 1.15 K higher than that of the sample doped with 8 wt % Y 2 O 3. The T C of sample doped with 8 wt% Y 2 O 3:Eu 3+ is 0.4 K higher than that of pure MgB 2. Results indicate that doping electroluminescent materials into MgB 2 increases the transition temperature; this novel strategy may also be applicable to other superconductors.

Effects of Bi-2212 addition on the levitation force properties of bulk MgB2 superconductors

We present a detailed investigation of the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) adding on the levitation force and magnetic properties of bulk MgB2 obtained by hot press method. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 10 wt%) of the total MgB2. Moreover, we present MgB2 bulk samples fabricated by using different production methods including hot pressing method to our knowledge. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano-boron (B) powder and Bi-2212 powder which are produced by hot press method. As a result of hot press process, compact pellet samples were manufactured. The vertical and lateral levitation force measurements were executed at the temperatures of 20, 24 and 28 K under zero-field-cooled (ZFC) and field-cooled (FC) regimes for samples with various adding levels. At 24 K and 28 K under ZFC regime, the 2 wt% Bi-2212 added sample exhibits a higher vertical levitation force than the pure sample. Bi-2212 added MgB2 samples compared to the pure sample have lower attractive force values in FC regime. The magnetic field dependence of the critical current density J c was calculated from the M-H loops for Bi-2212 added MgB2 samples. The 2 wt% Bi-2212 added sample has the best levitation and critical current density performance compared to other samples. The critical temperature (T c ) has slightly dropped from 37.8 K for the pure MgB2 sample to 36.7 K for the 10 wt% of Bi-2212 added sample. The transition temperature slightly decreases when Bi-2212 adding level is increased.

Competition of the nano-inclusions and the effects on critical current density in Ni and SiC co-doped MgB2 bulks

Samples of (MgB2)0.96Ni0.04 + x wt% SiC (with x = 0, 2, 5 and 10) were sintered at 750°C for 30 min, and the phase composition, microstructures, and superconducting properties were investigated. The highest critical current density (Jc) was obtained in the sample with 2 wt% SiC doping, owing to the precipitation of the nanoscale MgNi2.5B2 and Mg2Si on the edge of regular grains. The generation of the two impurities displayed a competition, and consequently the MgNi2.5B2 is refined to be effective pinning centre, which is in contrast to its influence in the Ni-doped sample. Results from differential thermal analysis and modified Flynn-Wall-Ozawa method also supported our explanation, and the best fitting mechanism function of solid-solid reaction in this system was ascertained. We conclude that 'Avrami-Erofeev, n = 2' is the best fitting mechanism function, indicating random nucleation followed by an instantaneous growth of nuclei. The function of the described mechanism, G(α), is 2[−ln(1 − α)]1/2, (α is the product fraction), which is different from that of pure MgB2.

Critical current densities in Ag-added bulk MgB2

In previous studies, we found that bulk MgB2 contained numerous voids in various shapes and sizes. With the aim of improving the critical current density as well as the mechanical performance of the disk-shaped MgB2 bulk superconductors, we added Ag and optimized the processing conditions. The samples with varied Ag content from 0, 2, 4, 6, to 10wt% were synthesized in pure Ar atmosphere. Microstructural observation by scanning electron microscopy confirmed that metallic Ag particles are embedded in the void regions. Furthermore, atomic force microscopy indicated that silver-based MgB2 particles are of nanometer size. As a result, the critical current density (Jc) values were improved with Ag addition as compared to pure MgB2 bulk. The sample with 4wt% Ag addition exhibited the highest Jc of 293kA/cm2 at 20K and self field. The respective Jc values at 10K were 400kA/cm2, 300kA/cm2, and 100kA/cm2 in self field, 1T and 2T. These values are the highest record values so far reported in bulk MgB2 materials.

The critical current reaction on hydrostatic pressure of a superconductor–semimetal composite

The transport characteristics of a composite consisting of microparticles of a superconductor MgB2 and nanopowder of a ferromagnetic half-metal La0.7Ca0.3MnO3 (LCMO) were investigated under hydrostatic compression. It was observed that as the concentration of the LCMO manganite is increased above the percolation threshold of MgB2, the superconducting current flows through the superconductor–ferromagnet–superconductor chains with the LCMO thickness exceeding the magnetic coherence length ξM in the half-metal (ξM ≤ 10 Å) by an order of magnitude. This behavior can be attributed to the presence of triplet superconducting correlations in the half-metal, which arise due to the spin-active surface of LCMO nanograins. An increase in pressure led to an increase in the critical current of the MgB2–LCMO composite, while the critical current and the transition temperature of pure MgB2 decreased under pressure.

Estimation of π and σ band contributions in the normal state electrical conductivity of (Bi, Pb)-2223 added MgB2 superconductors

Temperature dependence of the normal state electrical resistivity of polycrystalline MgB2 added with 0, 0.5, 1, 3 and 5wt. % of (Bi, Pb)-2223 (Bi1.8Pb0.26Sr2Ca2Cu3O10+x) superconducting powder have been investigated in the light of two band approach based on π and σ bands of MgB2 superconductor. The scattering rates (γσ, γπ) and residual resistivity (ρ0σ,ρ0π) of each band are estimated for the investigated samples. Our observation for pure MgB2 shows much higher scattering rate in π bands, as compared to σ bands and hence indicates ‘dirty’ nature of the samples. However, the addition of 2223 in MgB2 is found to enhance the scattering rate in both bands, but the enhancement is more pronounced in π bands as compared to σ bands. Contribution of each individual band towards the total electrical conductivity of 2223 added MgB2 pellets are separated. Our analysis confirms that σ band contribution shows a small increase with 2223 addition and reaches nearly 89% for 5wt. % 2223 added MgB2 polycrystalline pellets. The electron–phonon coupling constant (λ) of pure and 2223 added MgB2 pellets calculated using Mc-Millan expression is found to be nearly invariant with 2223 addition.