High-Pressure Synthesis and the Enhancement of the Superconducting Properties of FeSe0.5Te0.5.

A series of FeSe0.5Te0.5 bulk samples have been prepared using the high gas pressure and high-temperature synthesis (HP-HTS) method to optimize the growth conditions for the first time and investigated for their superconducting properties using structural, microstructure, transport, and magnetic measurements to reach the final conclusions. Ex situ and in situ processes are used to prepare bulk samples under a range of growth pressures using Ta-tube and without Ta-tube. The parent compound synthesized by convenient synthesis method at ambient pressure (CSP) exhibits a superconducting transition temperature of 14.8 K. Our data demonstrate that the prepared FeSe0.5Te0.5 sealed in a Ta-tube is of better quality than the samples without a Ta-tube, and the optimum growth conditions (500 MPa, 600 °C for 1 h) are favorable for the development of the tetragonal FeSe0.5Te0.5 phase. The optimum bulk FeSe0.5Te0.5 depicts a higher transition temperature of 17.3 K and a high critical current density of the order of >104 A/cm2 at 0 T, which is improved over the entire magnetic field range and almost twice higher than the parent compound prepared using CSP. Our studies confirm that the high-pressure synthesis method is a highly efficient way to improve the superconducting transition, grain connectivity, sample density, and pinning properties of a superconductor.

Cometal Addition Effect on Superconducting Properties and Granular Behaviours of Polycrystalline FeSe0.5Te0.5.

The enhanced performance of superconducting FeSe0.5Te0.5 materials with added micro-sized Pb and Sn particles is presented. A series of Pb- and Sn-added FeSe0.5Te0.5 (FeSe0.5Te0.5 + xPb + ySn; x = y = 0-0.1) bulks are fabricated by the solid-state reaction method and characterized through various measurements. A very small amount of Sn and Pb additions (x = y ≤ 0.02) enhance the transition temperature (Tconset) of pure FeSe0.5Te0.5 by ~1 K, sharpening the superconducting transition and improving the metallic nature in the normal state, whereas larger metal additions (x = y ≥ 0.03) reduce Tconset by broadening the superconducting transition. Microstructural analysis and transport studies suggest that at x = y > 0.02, Pb and Sn additions enhance the impurity phases, reduce the coupling between grains, and suppress the superconducting percolation, leading to a broad transition. FeSe0.5Te0.5 samples with 2 wt% of cometal additions show the best performance with their critical current density, Jc, and the pinning force, Fp, which might be attributable to providing effective flux pinning centres. Our study shows that the inclusion of a relatively small amount of Pb and Sn (x = y ≤ 0.02) works effectively for the enhancement of superconducting properties with an improvement of intergrain connections as well as better phase uniformity.

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.

Influence of Amorphous Boron Grain Size, High Isostatic Pressure, Annealing Temperature, and Filling Density of Unreacted Material on Structure, Critical Parameters, N-Value, and Engineering Critical Current Density in Mgb2 Wires.

Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (Birr), critical temperature (Tc), upper magnetic field (Bc2), engineered critical current density (Jec), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on Birr, Tc, Bc2, Jec, and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest Birr, Tc, Bc2, Jec, and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2.

Effect of Heat Treatments under High Isostatic Pressure on the Transport Critical Current Density at 4.2 K and 20 K in Doped and Undoped MgB2 Wires.

Annealing undoped MgB2 wires under high isostatic pressure (HIP) increases transport critical current density (Jtc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases Jtc by 25% in range magnetic fields from 2 T to 4 T and does not increase Jtc above 4 T at 20 K. Further research shows that a large amount of 10% SiC admixture and thermal treatment under a high isostatic pressure of 1 GPa significantly increases the Jtc by 40% at 4.2 K in magnetic fields above 6 T and reduces Jtc by one order at 20 K in MgB2 wires. Additionally, our research showed that heat treatment under high isostatic pressure is more evident in wires with smaller diameters, as it greatly increases the density of MgB2 material and the number of connections between grains compared to MgB2 wires with larger diameters, but only during the Mg solid-state reaction. In addition, our study indicates that smaller wire diameters and high isostatic pressure do not lead to a higher density of MgB2 material and more connections between grains during the liquid-state Mg reaction.

[High pressure processing of spices in atmosphere of helium for decrease of microbiological contamination]. / Zastosowanie wysokiego cisnienia w atmosferze helu do obnizenia zanieczyszczenia mikrobiologicznego przypraw ziolowych.

The aim of the study was to investigate the microbiological decontamination of coriander and caraway when HPP technology was applied in elevated temperature in helium atmosphere. The HPP and heat treatment was conducted for 30 minutes at 800 and 1 000 MPa and temperature range was 60 - 121 degrees C. Contamination with aerobic mesophilic bacteria was decreased by about 2 logarithmic cycles. Total elimination of coliform and yeast and moulds was observed. The efficacy of HPP treatment under helium atmosphere depended on the content of the water in tested samples. It can be concluded that high pressure treatment under atmosphere of helium, combination of proper high pressure and time improved the microbiological quality of spices.

The superconductor (Tl,Hg,Ca)2(Ba,Sr)2(Ca,Sr,Tl)Cu2O7.6.

In the title 2212-type superconductor (thallium mercury calcium barium strontium copper oxide), which contains both Tl and Hg in the charge reservoir (CR), Sr is located at both alkali-earth (AE) metal sites. Ca enters the CR at the same time as Tl shares the smaller AE site, which increases the apical Cu-Cu distance significantly. The structure causes the superconducting Cu-O layers to become significantly puckered.