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MgB 2 superconductor bulks were fabricated using Mg and B precursors. The physical state of Mg (solid, liquid, or gas) significantly influences the final product, MgB 2 bulk. In this study, the Solid-Solid, Liquid-Solid, and Gas-Solid methods were employed to fabricate MgB 2 bulks. The superconducting properties and microstructure of various samples were systematically investigated. Notably, for the first time, nano-CT was utilized to comprehensively and non-destructively analyze the microstructure of MgB 2 bulks, particularly the size and distribution of voids, which serve as the primary barrier affecting the superconducting properties. By examining the microstructure characteristics, the infiltration effect of Mg in different physical states during the reaction was analyzed, and a feasible reaction model was established. This research contributes to a better understanding of the reaction mechanism of MgB 2 , which may aid other researchers in enhancing the properties of MgB 2 superconductors. [ABSTRACT FROM AUTHOR]

This paper presents a novel two-step procedure for measuring the critical current (I c) properties as a function of tensile stress. The proposed method completely eliminates the possible negative effect of the voltage tap used during the tensile procedure, allowing the actual I c irreversible degradation stress to be clearly determined. Six different commercial REBCO tapes from five manufacturers were tested. The I c value does not degrade until the stress reaches the 'inflection area' in the tensile curve, which corresponds to the most pronounced transformation step from elastic to plastic deformation. This allows easy estimation of the stress corresponding to I c irreversible degradation by a simple and accurate cryogenic tensile curve instead of complicated in-situ I c tensile measurement. A feasible composite-material tensile model is established to explain the phenomenon. In addition, fatigue measurements on a commercial REBCO tape from Shanghai Superconductor technology show that the tape can withstand 10 000 cycles under 580 MPa and over 5000 cycles under 695 MPa, which also is consistent with the proposed composite-materials tensile model and is confirmed by the EBSD experiments on the Hastelloy substrate. This research provides better insight and tools for designing and fabricating extremely high-field magnets. [ABSTRACT FROM AUTHOR]

MgB 2 superconductor pellets were synthesized through Mg gas infiltration method using nanosized- and microsized B powders. There was a marked difference in the superconducting properties of the two samples, particularly in the pinning force and dominant pinning mechanism. The microstructures of the samples were observed using HR-TEM and STEM-HAADF, and the results showed that the primary reason for the difference in the superconducting properties is the distribution of the nanosized second-phase particle MgO. Additionally, a feasible reaction model for the Mg gas infiltration method was established. Compared to the Mg liquid infiltration method, the gas infiltration showed better penetrability ability with a small amount of residual Mg. This study presents a novel synthesis process to fabricate an MgB 2 pellet with superior density and superconducting properties. This method can be used in multiple applications such as superconducting bearings, compact superconductor magnets, and magnetic shielding. [ABSTRACT FROM AUTHOR]

Highlights • The malonic acid was proved to be an effective carbon source. • The carbon atoms were released by the reaction of Mg and CO 2. • The x value in Mg(B 1-x C x) 2 increased with a higher amount of malonic acid addition. • A moderate amount of malonic acid addition resulted in grain refinement. • Bulk MgB 2 with 10 wt% malonic acid addition showed the highest J c value. Abstract In this paper, malonic acid was tested as a new carbon source and its effects on the structural and superconducting properties of bulk MgB 2 have been systematically investigated. The detailed pyrolysis process of malonic acid was analyzed to understand the possible doping mechanism of malonic acid added MgB 2 samples. The weight fraction of MgO phase and the actual carbon substitution level in bulk MgB 2 increased with a higher amount of malonic acid addition, which was proven to be mainly caused by the reaction of Mg and CO 2 gas. A moderate amount of malonic acid addition resulted in grain refinement and enhanced flux pinning. Bulk MgB 2 with 10 wt% malonic acid addition showed much higher J c values in the entire magnetic field range. Three different doping methods with the same amount of malonic acid addition were compared. MgB 2 samples using malonic acid and ethanol processed boron showed the highest J c value, which was 7.2 times larger than that of the pure MgB 2 at 20 K and 5 T. [ABSTRACT FROM AUTHOR]

Abstract: One of the main challenges for coated conductor applications is to produce sharp cubic textured alloy substrates with high strength and low magnetism. In this work, the cubic textured Ni–7at.%W substrates were prepared from different powder metallurgy ingots by rolling-assisted biaxially textured substrate processing. The fabrication processes of cubic texture in the Ni–7at.%W tapes by two powder metallurgy routes are described in detail. Through the optimized process, full width at half maximum values of 6.7° and 5.0° were obtained, as estimated by X-ray (111) phi scan and (200) rocking curve in the textured Ni–7at.%W tape, respectively. By electron backscattering diffraction (EBSD) analysis, the percentage of the cubic textured component in the Ni–7at.%W tape surface was found to reach 97.0% within a tolerance angle smaller than 10°. Moreover, the formation mechanism of the cubic texture in the Ni–7at.%W tape were also investigated by EBSD. Particular attention was focused on the difference in the texture components along the thickness of the partially recrystallized samples. [Copyright &y& Elsevier]

The anisotropy of the critical current density of Fe-sheathed ex situ MgB2 monofilamentary tapes has been measured at various magnetic fields and temperatures and has been found to be influenced by the particle size of the starting material. Already reacted powders were milled in order to obtain different starting particle sizes. In order to understand the origin of the anisotropy, we have undertaken an X-ray study on the degree of texturing in the filaments after mechanical removal of the Fe sheath. The degree of texturing of the filaments at the interface Fe/MgB2 and at the center of the filaments has been determined. A moderate texture has been found, being slightly higher at the interface. [ABSTRACT FROM AUTHOR]

We report on a novel technique of sparking plasma sintering to prepare Ni–W alloy composite substrates with strong cube texture, high yield strength and reduced magnetization for coated conductors. It was found that an outer Ni–5at.% W layer in as-obtained composite substrates has a sharp and pure cube texture, while the use of the Ni alloy with high W content in the core of the composite substrates not only enhances the mechanical property, but also degrades the ferromagnetism of the whole substrates. [Copyright &y& Elsevier]

Abstract: A single Ce0.8Gd0.2O1.9 (CGO) buffer layer was successfully grown on the home-made textured Ni–5at.%W (Ni–5W) substrates for YBCO coated conductors by a simple metal–organic deposition (MOD) technique. The precursor solution was prepared using a newly developed process and only contained common metal–organic salts of both Ce and Gd dissolved into a propionic acid solvent. The precursor solution at 0.4M concentration was spin coated on short samples of Ni–5W substrates and heat-treated at 1100°C in a mixture gas of 5% H2 in Ar for an hour. X-ray studies indicated that the CGO films had good out-of-plane and in-plane textures with full-width-half-maximum values of 4.18° and 6.19°, respectively. Atomic force microscope (AFM) investigations of the CGO films revealed that most of the grain boundary grooves on the Ni–5W surface were found to be well covered by CGO layers, which had a fairly dense and smooth microstructure without cracks and porosity. These results indicate that our MOD technique is very promising for further development of single buffer layer architecture for YBCO coated conductors, due to its low cost and simple process. [Copyright &y& Elsevier]

A novel method of achieving microscopic morphologicalcontrol duringthe bulk synthesis of the high temperature superconducting ceramicYBa2Cu3O7(YBCO) has been studied.By incorporating appropriate amounts of the additives dextran (a biopolymer)and NaCl (a high melting point ionic salt) into the synthesis protocol,it is proven possible to engineer high aspect ratio (platelet) growthof the YBCO crystallites together with localized orientational orderingbetween adjacent densely packed crystallites. In the optimized protocol,both additives are fully consumed during the synthesis by decomposition(dextran) and vaporization (NaCl), leaving phase-pure YBCO as thefinal synthesis product. The individual effects of the two additivesare separately described and their optimal quantities determined.Routes toward improving the yield and increasing the aspect ratioof the resultingcrystallites are outlined. The method is likely applicable to thesynthesis of other ceramic materials as an alternative to the conventionalsolid state synthesis route, where a higher degree of connectivitybetween crystallites is required than can be achieved through sintering. [ABSTRACT FROM AUTHOR]