Robust Bulk Superconductivity by Giant Proximity Effect in Weyl Semimetal-superconducting NbP/NbSe2 Composites

We synthesize Weyl semimetal/superconductor NbP/NbSe2 composite and observe stable bulk superconductivity at Tc = 7.2 K, 6.9 K, and 6.8 K for NbSe2 crystal, NbP/NbSe2 (1:1), and NbP/NbSe2 (2:1) composites, respectively, despite large volume fraction of non-superconducting NbP phase. From the Ginzburg-Landau theory, the Hc2(0) is significantly enhanced in NbP/NbSe2 composites [22 T (1:1) and 18.5 T (2:1)] comparing with the pristine NbSe2 crystal (8 T). The bulk superconductivity in Weyl semimetal/superconductor composite cannot be simply described by the de Gennes-Meissner theory in a proximity effect. From the electrical transport, magnetization, and heat capacity measurement, we obtain various superconducting parameters. The superconducting properties indicate that the NbP/NbSe2 composite is far from the conventional BCS superconductivity. It suggests that the Weyl semimetal/superconductor composite can have giant proximity effect, resulting in the stable bulk superconductivity in a composite with sizable volume fraction of non-superconducting Weyl semimetals. The giant proximity effect in Weyl semimetal/superconductor interface can have a platform to investigate the proximity induced Weyl semimetallic superconducting states.

Prediction of Effective Permittivity of Foam-Polymer Materials

Porous plastics are used in various fields of industry, including radio- and electrotechnical fields. They are characterized by good heat- and sound isolating, dielectric and mechanical properties as well as by resistance to effect of various external factors during operation. The problem of estimation of effective permittivity of foam-polymer materials with a large volume fraction of pores, in particular, polyepoxide foam materials, has been considered. Two methods for solving it, both based on the matrix have been proposed. In the first method the matrix is considered as a polyepoxide binder, and the cavities filled with gas are taken as inclusions. In the second method the polyepoxide walls, separating cavities, are taken as inclusions, and gas filling cavities is considered as a matrix. To obtain the formulas for calculation, both methods use a generalized singular approximation of the theory of random fields. Based on the obtained expressions, the model calculations of the effective permittivity of a macroscopically isotropic foam material with a polymer binder based on E-20 and the cavities filled with freon, depending on the apparent density of the material, have been made. The calculations in the generalized singular approximations have been carried out for two of its variants: when the matrix was considered as a comparison medium; and, also by the self-consistent method. In the calculations using the second method two variants of the shape of the cells of the material have been considered: a weakly leaked or heavily leaked polyhedron. The calculated dependences obtained by all me-thods have shown the qualitative compliance with the experimental data.

Thickness-Dependent Permeation Properties of Quenched and Standard Laser-Sintered Polyamide 12 Sheets

The laser sintering of polymers is an additive manufacturing technology that is becoming increasingly established in the industrial environment. This study investigated the thickness-dependent permeation properties of laser-sintered (LS) polymers as required to design and produce components with a special barrier performance to gaseous substances. Helium and oxygen permeation experiments were carried out on quenched and standard LS polyamide 12 (PA12) sheets generated with two, four, six, and eight layers at a constant powder layer thickness of 100 µm. The structural properties of the sheets were examined by differential scanning calorimetry, light microscopy, and X-ray micro-computed tomography. A reduction in thickness resulted in higher diffusion coefficients for both types of LS sheets. An explanation could be the large volume fraction of poorly sintered powder particles adhering to the surfaces and incomplete melting and low consolidation of the polymer at small thicknesses. The thickness-dependency of the solubility coefficients was the opposite, especially for the standard LS sheets, which might be related to the larger pore volume in thicker sheets. As both effects compensated for each other, nearly constant permeation coefficients for all thicknesses were observed. The results provide further insights into different material characteristics of thin LS PA12 structures and offer new information on factors relevant to their solution and diffusion behavior.

Influence of Nb Content on Precipitation, Grain Microstructure, Texture and Magnetic Properties of Grain-Oriented Silicon Steel

The effects of Nb content on precipitation, microstructure, texture and magnetic properties of primary recrystallized grain-oriented silicon steel were investigated by various methods. The results show that the precipitates in primary recrystallized sheets are mainly MnS, Nb(C,N), composite precipitates of MnS and AlN, and composite precipitates of Nb(C,N) and AlN. Adding niobium could refine the primary recrystallized microstructure. The steel with 0.009 wt% Nb possesses the finest and the most dispersed precipitates, which contributes to the finest primary recrystallized microstructure due to the strong pinning force. Adding niobium is beneficial to obtain large volume fraction favorable texture for grain-oriented silicon steel, and the effect of Nb addition is not obvious when the content is higher than 0.009 wt%. After final annealing, the steel with 0.009 wt% Nb shows the best magnetic properties, B800 = 1.872 T, P1.7/50 = 1.25 W/kg.

Effects of Annealing on Microstructure and Mechanical Properties of Metastable Powder Metallurgy CoCrFeNiMo0.2 High Entropy Alloy

A CoCrFeNiMo0.2 high entropy alloy (HEA) was prepared through powder metallurgy (P/M) process. The effects of annealing on microstructural evolution and mechanical properties of P/M HEAs were investigated. The results show that the P/M HEA exhibit a metastable FCC single-phase structure. Subsequently, annealing causes precipitation in the grains and at the grain boundaries simultaneously. As the temperature increases, the size of the precipitates grows, while the content of the precipitates tends to increase gradually first, and then decrease as the annealing temperature goes up to 1000 °C. As the annealing time is prolonged, the size and content of the precipitates gradually increases, eventually reaching a saturated stable value. The mechanical properties of the annealed alloys have a significant correspondence with the precipitation behavior. The larger the volume fraction and the size of the precipitates, the higher the strength and the lower the plasticity of the HEA. The CoCrFeNiMo0.2 high entropy alloy, which annealed at 800 °C for 72 h, exhibited the most excellent mechanical properties with the ultimate tensile strength of about 850 MPa and an elongation of about 30%. Nearly all of the annealed HEAs exhibit good strength–ductility combinations due to the significant precipitation enhancement and nanotwinning. The separation of the coarse precipitation phase and the matrix during the deformation process is the main reason for the formation of micropores. Formation of large volume fraction of micropores results in a decrease in the plasticity of the alloy.

Crystal pathologies in macromolecular crystallography

Macromolecules, such as proteins or nucleic acids, form crystals with a large volume fraction of water, ~50% on average. Apart from typical physical defects and rather trivial poor quality problems, macromolecular crystals, as essentially any crystals, can also suffer from several kinds of pathologies, in which everything seems to be perfect, except that from the structural point of view the interpretation may be very difficult, sometimes even im-possible. A frequent nuisance is pseudosymmetry, or non-crystallographic symmetry (NCS), which is particularly nasty when it has translational character. Lattice-translocation defects, also called order-disorder twinning (OD-twinning), occur when molecules are packed regularly in layers but the layers are stacked (without rotation) in two (or more) discrete modes, with a unique translocation vector. Crystal twinning arises when twin domains have different orientations, incompatible with the symmetry of the crystal structure. There are also crystals in which the periodic (lattice) order is broken or absent altogether. When the strict short-range translational order from one unit cell to the next is lost but the long-range order is restored by a periodic modulation, we have a modulated crystal structure. In quasicrystals (not observed for macromolecules yet), the periodic order (in 3D space) is lost completely and the diffraction pattern (which is still discrete) cannot be even indexed using three hkl indices. In addition, there are other physical defects and phenomena (such as high mosaicity, diffraction anisotropy, diffuse scattering, etc.) which make diffraction data processing and structure solution difficult or even impossible.

The Effect of Mixing Ratios on Pore Properties of Fe Foam Fabricated Using Slurry Coating Process

Metal foams have a cellular structure consisting of a solid metal containing a large volume fraction of pores. In particular, open, penetrable pores are necessary for industrial applications such as in high temperature filters and as support for catalysts. In this study, Fe foam with greater than 90% porosity, 2-mm pore size was successfully fabricated using a slurry coating process and the pore properties were characterized. The Fe and Fe2O3 powder mixing ratios were controlled to produce Fe foam samples with different pore sizes and porosity. First, the slurry was prepared through the uniform mixing of powders, distilled water, and polyvinyl alcohol (PVA). The amount of slurry coated on the PU foam increased with theFe2O3 mixing powder ratio, but the shrinkage and porosity of the Fe foams decreased, respectively, with increasing Fe2O3 mixing powder ratio.

The Effect of Graded Structure of Sintered Iron-Manganese Biomaterials on the Range and Distribution of Local Hardness Values

Powders comprised of Fe particles and 25, 30, 35wt.% of Mn particles were mixed, compacted and sintered to investigate the effect of Mn on the properties of sintered Fe-Mn alloys. It was found that the sample’s swelling, microstructure and distribution of local hardness values were strongly affected by the Mn content. The particles in Fe-25Mn and Fe-30Mn samples exhibited a distinct onion-like structure causing a considerable variability in local properties, while the particles in Fe-35Mn samples were at a glance more homogeneous, with a large volume fraction occupied by a nearly uniform material with almost constant properties.

Effect of Sintering Temperature on the Superconducting Properties of MgB2 Superconductor Co-Added with a High Concentration of Si and C

In this study, as much as 10 and 15 wt.% nanosized silicon and carbon (Si+C) were reacted with (Mg+2B) at 650°C and 850°C, respectively, for 1 hour. The phase formation, surface morphology and superconducting properties of these samples were evaluated. The relative peak intensity as calculated from the XRD patterns indicates the formation of large Mg2Si volume fraction at low sintering temperature. MgB4phase was detected in the samples sintered at high temperature as a result of Mg deficiency. The C substitution level as estimated from the lattice parameters, was shown to increase in the samples reacted with a higher amount of (Si+C) at high temperature. Scanning electron micrograph showed that (Si+C) co-addition had refined the grain size and improved the grain coupling of MgB2. The superconducting transition temperature was found to decrease with increasing addition level. The superconducting transition width was also broadened because of a large volume fraction of secondary phases. The improved field dependent critical current density at both 5 K and 20 K is accounted to enhanced scattering by C substitution and grain boundary pinning.