Study on the Relationship between Uniaxial Strain and Critical Transition Temperature of MgB2 Based on First-principles

It has been shown that the critical transition temperature (Tc) of MgB2 superconducting materials decreases with the increase of hydrostatic pressure, but this is a comprehensive Tc change after multiaxial strain, and the influence of strain on Tc is not clearly understood. In this paper, based on the McMillan superconducting calculation formula and the first-principles density functional theory, the Tc change of MgB2 under uniaxial strain and the properties of MgB2 such as energy band, Fermi surface, differential charge density and phonon dispersion spectrum under uniaxial strain are studied, and the relationship between uniaxial strain and these properties is analyzed. The calculated Tc of MgB2 at zero strain is 38.35 K, which is in good agreement with the experimental value of 39 K. When the a-axis strain is 1%, the Tc value can be increased to 49.7 K, and there is a further improvement trend. When the a-axis compression strain is -1%, Tc decreases to 31.52 K. When the c-axis tensioncompression strain is applied, the change of Tc value is small. Further analysis shows that the influence of a-axis strain on the differential charge density, electronic band structure, phonon dispersion and other properties of MgB2 is significantly greater than that of c-axis strain, and the influence of these properties on Tc is discussed. The work in this paper has certain theoretical and guiding significance for the preparation of MgB2 with higher Tc and the study of the effect of uniaxial strain on Tc of superconducting materials.

Relationship between the TC of Smart Meta-Superconductor Bi(Pb)SrCaCuO and Inhomogeneous Phase Content

A smart meta-superconductor Bi(Pb)SrCaCuO (B(P)SCCO) may increase the critical transition temperature (TC) of B(P)SCCO by electroluminescence (EL) energy injection of inhomogeneous phases. However, the increase amplitude ΔTC (ΔTC=TC−TC,pure) of TC is relatively small. In this study, a smart meta-superconductor B(P)SCCO with different matrix sizes was designed. Three kinds of raw materials with different particle sizes were used, and different series of Y2O3:Sm3+, Y2O3, Y2O3:Eu3+, and Y2O3:Eu3++Ag-doped samples and pure B(P)SCCO were prepared. Results indicated that the TC of the Y2O3 or Y2O3:Sm3+ non-luminescent dopant doping sample is lower than that of pure B(P)SCCO. However, the TC of the Y2O3:Eu3++Ag or Y2O3:Eu3+ luminescent inhomogeneous phase doping sample is higher than that of pure B(P)SCCO. With the decrease of the raw material particle size from 30 to 5 μm, the particle size of the B(P)SCCO superconducting matrix in the prepared samples decreases, and the doping content of the Y2O3:Eu3++Ag or Y2O3:Eu3+ increases from 0.2% to 0.4%. Meanwhile, the increase of the inhomogeneous phase content enhances the ΔTC. When the particle size of raw material is 5 μm, the doping concentration of the luminescent inhomogeneous phase can be increased to 0.4%. At this time, the zero-resistance temperature and onset transition temperature of the Y2O3:Eu3++Ag doped sample are 4 and 6.3 K higher than those of pure B(P)SCCO, respectively.

Observation of small Fermi pockets protected by clean CuO2 sheets of a high-Tc superconductor

In cuprate superconductors with high critical transition temperature (Tc), light hole-doping to the parent compound, which is an antiferromagnetic Mott insulator, has been predicted to lead to the formation of small Fermi pockets. These pockets, however, have not been observed. Here, we investigate the electronic structure of the five-layered Ba2Ca4Cu5O10(F,O)2, which has inner copper oxide (CuO2) planes with extremely low disorder, and find small Fermi pockets centered at (π/2, π/2) of the Brillouin zone by angle-resolved photoemission spectroscopy and quantum oscillation measurements. The d-wave superconducting gap opens along the pocket, revealing the coexistence between superconductivity and antiferromagnetic ordering in the same CuO2 sheet. These data further indicate that superconductivity can occur without contribution from the antinodal region around (π, 0), which is shared by other competing excitations.

Electrospinning Synthesis of Bi-2223 Superconducting Nanowires

This paper presents the synthesis and characterization of Bi2Sr2Ca2Cu3O8+x superconducting nanowires. Bi2Sr2Ca2Cu3O8+x nanowires with Tc = 68 K were synthesized using the electrospinning process employing sol–gel precursors. A sol–gel methodology was used to obtain a homogeneous PVP solution containing Bi, Sr, Ca, and Cu oxalates. Samples were heat-treated at 120 °C to remove excess moisture, and then at 850 °C in box furnace. Bulk sample was also prepared using coprecipitation method for comparison. Based on XRD, the nanowire sample showed minimal Bi-2223 phases and apparent Bi-2212 phases. The morphology, microstructure, and crystal structure of these nanowires were examined using field emission scanning electron microscopy (FESEM) to reveal a rectangular morphology having typical wire thickness in the range of 150–1000 nm. Electrospun Bi-2223 were grinded and pressed at 0.9 GPa into pellets. DC measurements were conducted to investigate the critical transition temperature (Tc) of Bi-2223 nanowires and to compare their magnetic properties to those of coprecipitated Bi-2223 pellets. The Tc for the bulk sample is observed at 101 K and electrospun Bi-2223 at 68 K. Coprecipitated Bi-2223 was added with Pb whereas electrospun Bi-2223 does not employ Pb. These results point to the existence of utilizing of the substitution of Pb with Bi; Bi-2223 phases in pressed nanowire are less, and the potential of using electrospinning to synthesis functional Bi-2233 superconductors.

Effect of CeO2 Nanoparticle on the Structural and Electrical Properties of BSCCO-2223 High Temperature Superconductor

A study of the effects of Cerium oxide nanoparticle doped with BSCCO-2223 on the microstructure and superconducting properties was carried out. All samples were synthesized using solid state reaction method. Ce concentration is varied from x = 0.0 up to 0.1 in a general stoichiometry of Bi1.6Pb0.4Sr2Ca1-xCexCu3Oy. The samples were characterized structurally and electrically by X-Ray Diffraction (XRD) and four-point probe method respectively. XRD analysis shows that both (Bi,Pb)-2212 and (Bi,Pb)-2223 phases coexist in the samples having tetragonal crystal structure but changed to orthorhombic when x=0.10. The values of critical transition temperature, TC and critical current density, JC of the samples decreased with the increase in Ce concentration. The possible reasons for the observed degradation in superconducting and structural properties of Bi-2223 due to Ce nanoparticles addition were discussed.

The effects of sintering temperature on superconductivity of MgB2 prepared by hot pressing

The [Formula: see text] superconductor bulks were prepared by hot-pressing under the pressure of 55 MPa at different temperatures of 650[Formula: see text]C, 700[Formula: see text]C, 800[Formula: see text]C, 900[Formula: see text]C, 1000[Formula: see text]C, respectively, and the hot-pressing effects on the superconducting properties of [Formula: see text] bulks were investigated. The density of bulk samples increased with the rise of sintering temperature and the density reached to the maximum value when the sintering temperature rose to 1000[Formula: see text]C. For the sample sintered at 1000[Formula: see text]C, the critical transition temperature ([Formula: see text] reached the highest value of 38.8 K despite the high content of [Formula: see text] (30.62 wt.%). However, the critical current density ([Formula: see text] did not increase with the increase in the density and [Formula: see text]. The sample sintered at 700[Formula: see text]C maintained the high superconducting volume and had a small grain size, thus providing the best magnetic flux pinning force and [Formula: see text]. An effective hot-pressing process to improve [Formula: see text] might be the way to prepare by further increasing the density of sintering samples at 700[Formula: see text]C.

Спин-переориентационный переход в микропроводах alpha-Fe с аморфной оболочкой PrDyCoFeB

A spin-reorientation transition accompanied by a decrease in the longitudinal magnetization of α-Fe/PrDyCoFeB microwires was observed at 245 K in zero magnetic field. An increase of the magnetic field at which the microwire is heated from 2 K leads to a significant shift of the transition temperature from 245K at 0 T to 70 K at 1 T. In the perpendicular direction, the change in magnetization at the critical transition temperature is almost absent. Jumps of the magnetic anisotropy and magnetic susceptibility are observed in low fields at a critical temperature. The magnetic phase transition is due to a transition between the ferrimagnetic state of the PrDyCoFeB shell at high temperatures and the state of Ising spin glass at low temperatures.

Tuning oxygen vacancy and growth step for the high performance of Nd1+xBa2−xCu3Oy bulk cryomagnets

The Nd1+xBa2−xCu3Oy superconductor is considered to be one of the most promising materials in the REBaCu3Oy family owing to its excellent properties of high critical transition temperature (Tc) and high current density.

Synthesis of NiO Nanotubes via a Dynamic Thermal Oxidation Process

Nickel oxide (NiO) nanotubes were synthesized via a thermal oxidation process from Ni nanowires. The effects of oxidation temperature on the morphology, microstructures, and composition of nanowires were investigated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show that the Ni nanowires convert initially to Ni/NiO core-shell nanowires with increasing annealing temperatures, and then to the nanotubes at the critical transition temperature of about 425 °C. Our findings provide useful information for the preparation of NiO nanotubes to meet the required applications.