High Performance Bi-2212 Round Wires Made with Recent Powders

Progress on the Fabrication of Superconducting Wires and Tapes via Hot Isostatic Pressing

Fabrication of high-performance superconducting wires and tapes is essential for large-scale applications of superconducting materials. The powder-in-tube (PIT) method involves a series of cold processes and heat treatments and has been widely used for fabricating BSCCO, MgB₂, and iron-based superconducting wires. The densification of the superconducting core is limited by traditional heat treatment under atmospheric pressure. The low density of the superconducting core and a large number of pores and cracks are the main factors limiting the current-carrying performance of PIT wires. Therefore, to improve the transport critical current density of the wires, it is essential to densify the superconducting core and eliminate pores and cracks to enhance grain connectivity. Hot isostatic pressing (HIP) sintering was employed to improve the mass density of superconducting wires and tapes. In this paper, we review the development and application of the HIP process in the manufacturing of BSCCO, MgB₂, and iron-based superconducting wires and tapes. The development of HIP parameters and the performance of different wires and tapes are reviewed. Finally, we discuss the advantages and prospects of the HIP process for the fabrication of superconducting wires and tapes.

A flexible neutron spectrometer concept with a new ultra-high field steady-state vertical-bore magnet

The proposed facility explores materials under ultra-high magnetic fields. By combining the power of high fields to tune materials and of neutron scattering to probe the resulting changes down to the atomic scale, this facility will enable transformative progress in the study of quantum materials and is named for the "TITAN" subset of Greek gods to reflect this transformation. TITAN will offer DC magnetic fields up to at least 20 T. Exploiting the record brightness and bandwidth of the Second Target Station at the Spallation Neutron Source, TITAN will probe atomic-scale responses through high efficiency neutron spectroscopy up to 80 meV energy transfer, high resolution diffraction, and small angle neutron scattering. Focusing neutron optics will maximize flux on accurately positioned samples, while radial collimation and optimized shielding and detection strategies will minimize backgrounds.

Modeling of lattice parameters of cubic perovskite oxides and halides

Perovskites having the chemical formulae of ABX3 are promising candidates for various electronic, magnetic, and thermal applications. One of the important structural factors is a (the lattice constant), which represents the unit cell size. The variation in the lattice constant is a combined result of interactions between different ions, determined by valence electrons and ionic radii. The size and stability of unit cells have important influences on structural stabilities, bandgap structures, and therefore performance of materials. To obtain the lattice constant of cubic perovskites without going through experimental efforts such as synthesis and measurements, we construct a model based on Gaussian process regressions for cubic perovskite lattice constant predictions. The model utilizes the number of valence electrons as well as ionic radii of alloying elements as predictors. A total of 149 cubic perovskites containing fluorides, chlorides, and bromides with cation combinations of A1+B2+, as well as oxides with cation combinations of A1+B5+, A2+B4+, and A3+B3+ are explored. The model demonstrates good performance in terms of stabilities and accuracy, and thus could be a rapid approach to estimate lattice constants.

Transport current and magnetization of Bi-2212 wires above liquid Helium temperature for cryogen-free applications

Since the discovery of high temperature superconductors, a possible cryogen-free scenario has always been wished. Nowadays, liquid Helium is running out, and it is likely that the cooling by will be a large part of the costs of any superconducting system. Bi-2212 wires at temperature higher than 4.2 K still show a very high irreversibility field and thus a deep investigation of their properties in such a range of temperature is very useful in order to assess the applicability in high field cryogen-free magnets. Here electrical transport and magnetic properties characterization at variable temperature and magnetic field on our "GDG-processed" wires are reported together with a well-described original approach to calculate the irreversibility field H_irr. This study is devoted to provide reference data on the behaviour of the only isotropic wire for high field application with an eye to the performances at temperatures above 4.2 K.

Superconducting materials: Challenges and opportunities for large-scale applications

Superconducting materials hold great potential to bring radical changes for electric power and high-field magnet technology, enabling high-efficiency electric power generation, high-capacity loss-less electric power transmission, small lightweight electrical equipment, high-speed maglev transportation, ultra-strong magnetic field generation for high-resolution magnetic resonance imaging (MRI) systems, nuclear magnetic resonance (NMR) systems, future advanced high energy particle accelerators, nuclear fusion reactors, and so on. The performance, economy, and operating parameters (temperatures and magnetic fields) of these applications strongly depend on the electromagnetic and mechanical properties, as well as the manufacturing and material cost of superconductors. This perspective examines the basic properties relevant to practical applications and key issues of wire fabrication for practical superconducting materials, and describes their challenges and current state in practical applications. Finally, future perspectives for their opportunities and development in the applications of superconducting power and magnetic technologies are considered.

Crystal Growth and High-Pressure Effects of Bi-Based Superconducting Whiskers

Three growth methods were tested for producing high-transition temperature superconducting Bi₂Sr₂Ca _n-1Cu _n O_2n+4+δ whiskers, employing different ways to focus a compressive stress and size effect of the precursors. First, thermographic imaging was used to investigate thermal stress from temperature distribution in the precursors during growth annealing. To enhance thermal stress in the precursors, a thermal cycling method and a Ag-paste coating method were proposed and found to significantly accelerate the whisker growth. The use of pulverized precursors also promoted whisker growth, possibly due to contribution from the vapor-liquid-solid growth mechanism. The obtained whiskers revealed the typical composition, diffraction patterns, and superconducting properties of the Bi-2212 phase. The proposed methods were able to stably produce longer whiskers compared to the conventional method. Using the obtained whiskers, electrical transport measurements under high pressure were successfully performed up to around 50 GPa.

Process to densify Bi2Sr2CaCu2Ox round wire with overpressure before coil winding and final overpressure heat treatment

Overpressure (OP) processing of wind-and-react Bi₂Sr₂CaCu₂O_x (2212) round wire compresses the wire to almost full density, decreasing its diameter by about 4 % without change in wire length and substantially raising its J _c . However, such shrinkage can degrade coil winding pack density and magnetic field homogeneity. To address this issue, we here present an overpressure predensification (OP-PD) heat treatment process performed before melting the 2212, which greatly reduces wire diameter shrinkage during the full OP heat treatment (OP-HT). We found that about 80 % of the total wire diameter shrinkage occurs during the 50 atm OP-PD before melting. We successfully wound such pre-densified 1.2 mm diameter wires onto coil mandrels as small as 10 mm diameter for Ag-Mg-sheathed wire and 5 mm for Ag-sheathed wire, even though such small diameters impose plastic strains up to 12% on the conductor. A further ~20% shrinkage occurred during a standard OP-HT. No 2212 leakage was observed for coil diameters as small as 20 mm for Ag-Mg-sheathed wire and 10 mm for Ag-sheathed wire, and no J _c degradation was observed on straight samples and 30 mm diameter coils.