Magnetic Field Current Density Research Articles

Monte Carlo simulation study on BaMO3 nanostructures in BMO-doped REBa2Cu3O y thin films prepared by Vapor-Liquid-Solid technique

Abstract In depositing REBa2Cu3O y (REBCO) superconducting thin films, the Vapor-Liquid-Solid (VLS) technique offers advantages over usual pulsed laser deposition (PLD) for achieving high deposition rates and controlled crystal orientation. However, introducing BaMO3 (BMO) additions into REBCO thin films to enhance critical current density in magnetic fields can lead to distinct nanostructures compared to PLD. While simulations have explored nanorod morphologies in PLD. However, a comprehensive understanding of BMO nanostructure self-organization in VLS growth remains elusive. This study presents a novel simulation approach that incorporates the liquid phase as droplets and motion of them within the VLS process. This model successfully reproduces experimental observed BMO nanostructures in VLS growth, providing valuable insights and a practical guideline for tailoring BMO nanostructures using the VLS technique.

Enhancement of critical current densities by co-doping with Zr, Sn and Ce for Gd123 thin films fabricated by fluorine-free MOD method

Abstract We have fabricated GdBa2Cu3O7-δ thin films co-doped several types of BaMO3 (M=Zr, Sn, Ce) artificial pinning centers with different lattice constants and Young’s modulus from 2.0 to 5.0 mol% on LaAlO3 single crystal substrates by the FF-MOD method. When several types of BaMO3 are simultaneously introduced into Gd123 films by the FF-MOD method, Ba required for BaMO3 crystal growth is shared among them, each crystal growth is suppressed, and thus the crystals become finer and denser. This resulted in a remarkable enhancement of the critical current densities in magnetic fields. The maximum J c of 16.57 MA cm-2 at 0 T and 1.97 MA cm-2 at 3.0 T, 30 K obtained for the Gd123 film introduced three types of BaMO3 (M=Zr, Sn, Ce) with 4.0 mol% were 1.22 and 1.76 times larger than those for the film with the same amount of BaCeO3. This method shows a new strategy to improve Jc in magnetic fields of REBCO.

Effects of Precursor Film Thickness and Heat-Treatment Temperature On Joint Rate for a GdBa2Cu3Oy Superconducting Joint

GdBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (GdBCO) coated conductors (CCs) are promising wire materials because of their high critical temperature and critical current density in magnetic fields. The CCs must contain superconducting joints to create long wires. Previously, we fabricated a GdBCO CC with a superconducting joint by face-to-face crystallization of two CC samples with a GdBCO precursor film. To obtain a high current and low resistance, the crystallinity of GdBCO and a wide joint area are key considerations. This study investigates the effect of the heat-treatment temperature and precursor film thickness on these two factors. GdBCO samples were prepared without or with a precursor film of ∼50–200 nm thickness via pulsed laser deposition. The samples were set face-to-face and crystallized at 700-820 °C under a mechanical pressure of 40 MPa in an electric furnace. X-ray diffraction (XRD) analysis and optical microscopy revealed that both the peak intensity ratio of crystallized GdBCO and the joint rate at 800 °C were respectively 1.5 and 1.6 times higher than that at 720 °C. As the precursor film thickness increased from 50– 200 nm, the joint rate increased from 15.7– 25.4%, indicating that the heat treatment at ∼800 °C with a thick precursor film, is suitable. The results of this article lead to that the proposed method used in GdBCO CCs to reduce the electrical resistance.

Crystal Growth Simulation of BMO Nanorods in BMO-Doped REBCO Films With Seed layers

The self-organization of BaMO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BMO) nanorods in REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> films is important for enhancing the superconducting properties in magnetic fields. We previously reported the control of BMO self-organization using the seed layer technique, which included the low-temperature growth (LTG) technique. The LTG technique can achieve a high number density of BMO nanorods and excellent critical current density in magnetic fields at 4.2 K. To clarify the self-organization mechanism of BMO nanorods, we develop a three-dimensional Monte Carlo simulation and investigate the effect of the seed layer technique on the growth of BMO nanorods. Results show that the number density of BMO nanorods is affected by the seed layer deposited at a low deposition rate (v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DR</sub> ) and/or high substrate temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ). Moreover, we propose a growth kinetic factor (R) that includes v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DR</sub> , T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , and BMO volume fraction. Our simulation results of the number density are affected by R; therefore, Ris useful for predicting the number density of BMO nanorods.

Effect on SmBa2Cu3Oy films of lattice strain induced by BaHfO3 nanorods

BaMO3 (BMO, M=Zr, Sn, Hf, etc.) is well known to undergo self-organisation into many nanorods in a REBCO film grown by vapour phase epitaxy. However, REBCO experiences strain resulting from the BMO nanorods and this strain causes the superconducting properties to deteriorate. In this study, we prepared SmBCO films containing 16 vol% BaHfO3 (BHO) using a pulsed laser deposition method. Deposition was accomplished by using a low-temperature growth (LTG) technique to grow the films even at low substrate temperatures. By decreasing the substrate temperature, the number density of the BHO nanorods, which is estimated from the critical current density in magnetic fields and the irreversibility line, increased and their diameter decreased. The lattice strain exerted upon SmBCO and BHO could conveniently be evaluated by conventional X-ray diffraction owing to the substantial BHO content. This evaluation indicated that, as the substrate temperature decreased, the tensile strain exerted upon SmBCO decreased, whereas the compressive strain experienced by BHO increased. These results indicate that the effect of stress exercised by the narrow nanorods on REBCO is small. Our findings suggest LTG to be an effective technique to prepare REBCO films with a high number density of BMO nanorods owing to the small amount of stress induced by these nanorods.

The microstructure of Nb3Sn superconductors differing in the number of copper inserts at various stages of heat treatment

Superconducting materials with a high critical current density in magnetic fields up to 16 T at a temperature of 4.2 K are required to create magnetic systems of high-energy physics devices. We have studied the change of the microstructure of model samples of various designs with an internal tin source, differing in the number of copper separators (three, six and without them) at different stages of heat treatment. The formation of the following intermediate phases was studied: Cu3Sn, Cu6Sn5 and triple Cu-Sn-Nb phase after annealing at 370°C/100 h, by the use of scanning and transmission electron microscopy. The formation of the Nb6Sn5 phase on Nb filaments located close to the tin source and copper separators was studied after heat treatment at a temperature of 665°C from 10 minutes to 25 hours. The results of the analysis led us to understand the kinetics of the Nb3Sn and Nb6Sn5 formation in internal tin superconductors with an increased current-carrying capacity and a low level of hysteresis losses.

Design and Demonstration of a Double-pancake Coil for SMES using MgB2 Multi-strand cable

MgB2 round wires are now commercially available with applicable critical current density in magnetic fields up to 5 T. One of the promising applications using MgB2 is a superconducting magnetic energy storage (SMES) coil. In our project, multi-strand cables with 600 A nominal current are designed for double-pancake (DP) coils with 400 mm inner diameter. The coil production processes in our project are wind-and-react (W&R) and react-and-wind (R&W) methods, in which a Rutherford-type cable consisting of eight (W&R) or ten wires (R&W) with specific twist pitch is reacted and then used to wind the DP coils, to investigate the suitable manufacturing process for MgB2 coils. The final goal is to fabricate five-stacked DP coils, made up of four DP coils by the R&W method and one DP by the W&R method with a total number of 512 turns, forming a 30 kJ SMES coil and to demonstrate compensation of voltage fluctuation on the BUS line of 48 V DC in a micro grid consisting of renewable energy source and liquid hydrogen supply system in our project. The first DP coils made by the two manufacturing processes are constructed and tested with regard to their properties such as critical current density in liquid helium to keep uniform temperature distribution throughout the coils.

Optimization of BaHfO3 Doping Concentration as Secondary Phase in Y0.5Gd0.5Ba2Cu3O7−x Thin Film Prepared by Pulsed Laser Deposition

BaHfO3 (BHO)-doped Y0.5Gd0.5Ba2Cu3O7−x (YGBCO) films with a series of doping concentrations (1, 3, 5, and 10 mol%) were fabricated on CeO2 buffer layers by pulsed laser deposition (PLD) technique, and a pristine YGBCO film was also deposited at the same conditions for comparison. X-ray diffraction (XRD) results showed that the undoped and doped YGBCO films had a pure c-axis orientation. While the surface morphology and crystal quality of the BHO-doped YGBCO films deteriorated as the BHO content increased, and the critical current density (J c) at 77 K and self-field ( $J_{\mathrm {c}}^{77,0})$ and critical transition temperature (T c) of the BHO-doped YGBCO films exhibited varying degrees of decline in comparison with the pristine YGBCO film. However, the 5 mol% BHO-doped YGBCO film exhibited greatly enhanced the J c and the highest pinning force densities (F p) at both 4.2 and 65 K, which showed the maximum value of 5776 GN/m3 (4.2 K, H//c) and 117 GN/m3 (65 K, H//c), about 1.5 times that of the undoped YGBCO film. Based on the results, the 5 mol% BHO-doped YGBCO film had the most effective flux pinning centers, which are responsible for strongly improved critical current densities in magnetic fields.

In-field critical current property of IBAD/PLD coated conductors

REBa2Cu3Oy, (RE : rare earth elements, RE123) coated conductors are expected to show high performance in superconducting applications, due to their high mechanical strength and high current density in magnetic fields. Fujikura has developed ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) technique, and today we routinely manufacture coated conductors with length over 500 m and Ic over 500 A/cm-width at 77 K, self field. We have also been able to fabricate long conductors with higher Ic by thickening RE123 layer. Although Ic performances at 77 K, self field are important, but performances in magnetic fields at lower temperatures below 77 K are more important for coil applications. In this work, we evaluated coated conductors with thick RE123 layer in magnetic fields at low temperatures. All samples are fabricated with long length. We measured samples by four-probe transport method at wide temperature range from 77 K to 10 K by using cryo-cooled cryostat. A conductor with 5.5 μm thick RE123 exhibits high Ic values of 937 A/cm-width at 77 K, self field, 637 A/cm-width at 50 K, 5T and 976 A/cm-width at 40 K, 5T.

φ20 cm 室温ボアRE 系5 T 高温超電導マグネットの開発

REBa2Cu3Ox (REBCO, RE = rare-earth) coated conductors are expected to show high performance in superconducting applications because of their high mechanical strength and high current density in magnetic fields. More characteristics data of REBCO coils with larger diameters are required for use of these conductors in practical superconducting applications. We fabricated a cryo-cooled high-temperature superconducting (HTS) magnet, which was composed of 24 pancake coils with an inner diameter of 260 mm, using REBCO coated conductors. The stored energy of the magnet was 426 kJ. The total length of the REBCO coated conductors was approximately 7.2 km. These conductors were laminated with a copper stabilizer and were fabricated by Fujikura Ltd. using ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) methods. Before fabricating the magnet, all pancake coils were evaluated in terms of their V-I characteristics in liquid nitrogen in order to confirm the characteristics without degradation. After the fabrication, the magnet was cooled down to 24 K using a GiffordMcMahon (GM) cryocooler. We were successful in excitation of the magnet up to 5 T. Furthermore, we confirmed that a 1% current reversal of the coil current could stabilize the axial central magnetic field drift of the magnet.

Effect of low-temperature treatment and subsequent high-temperature annealing on the critical current density of YBa2Cu3O y

The field dependences of the critical current density of the HTSC compound YBa2Cu3O y recovered at T = 920–950°C after the low-temperature treatment have been investigated. At T = 200°C, structural defects are formed in a wet environment, which are capable of initiating pinning of magnetic vortices. A short-term (1–3 h) recovery annealing performed at T = 930–950°C leaves in the samples a fairly large amount of structural defects formed during the low-temperature treatment, which results in a substantial increase in the critical current density in magnetic fields of ∼2 T as compared to the ceramics not subjected to double annealing. A longer high-temperature treatment removes the structural defects formed and brings the electrophysical properties of YBa2Cu3O y to the level characteristic of the ceramics produced by standard technology.

Thickness dependence of Ic and Jc of LTG-SmBCO coated-conductor on IBAD-MgO tapes

We have reported SmBa2Cu3Oy (SmBCO) films on single crystalline substrates prepared by low-temperature growth (LTG) technique. The LTG-SmBCO films showed high critical current densities in magnetic fields compared with conventional SmBCO films prepared by pulsed laser deposition (PLD) method. In this study, to enhance critical current (Ic) in magnetic field, we fabricated thick LTG-SmBCO films on metal substrates with ion-beam assisted deposition (IBAD)-MgO buffer and estimated the Ic and Jc in magnetic fields.All the SmBCO films showed c-axis orientation and cube-on-cube in-plane texture. Tc of the LTG-SmBCO films were 93.1–93.4K. Jc and Ic of a 0.5μm-thick SmBCO film were 3.0MA/cm2 and 150A/cm-width at 77K in self-field, respectively. Those of a 2.0μm-thick film were 1.6MA/cm2 and 284A/cm-width respectively. Although Ic increased with the film thickness increasing up to 2μm, the Ic tended to be saturated in 300A/cm-width. From a cross sectional TEM image of the SmBCO film, we recognized a-axis oriented grains and 45° grains and Cu–O precipitates. Because these undesired grains form dead layers, Ic saturated above a certain thickness. We achieved that Ic in magnetic fields of the LTG-SmBCO films with a thickness of 2.0μm were 88A/cm-width at 1T and 28A/cm-width at 3T.

Strongly enhanced flux pining of GdBCO coated conductors with BaSnO3 nanorods by pulsed laser deposition

We report the effects of BSO addition on the crystallinity, texture, and the field dependency of critical current density (Jc) of GdBCO coated conductors (CCs) prepared by pulsed laser deposition (PLD). Undoped and BSO-doped GdBCO films showed only c-axis oriented growth, and the incorporated BSO nanorods exhibited epitaxial relationship with the GdBCO matrix. In comparison with undoped film, BSO-doped GdBCO film exhibited greatly enhanced Jc and higher pinning force densities in the entire field region of 0–5T (H//c) at 77 and 65K. The BSO-doped GdBCO film showed the maximum pinning force densities (Fp) of 6.5GN/m3 (77K, H//c) and 32.5GN/m3 (65K, H//c), ∼2.8 times higher than those of the undoped sample. Cross-sectional TEM analyses exhibited nano-structured BSO nanorods roughly aligned along the c-axis of the GdBCO film, which are believed effective flux pinning centers responsible for strongly improved critical current densities in magnetic fields.

Magnetic Properties of FeSeTe Compound Crystallized from Liquid Phase

We report on measurements of samples with nominal composition FeSe0.5Te0.5, crystallized by the Bridgman method. Magnetic and transport properties of the samples were examined. The measurements confirm the coexistence of ferromagnetism and superconductivity below the superconducting transition temperature. The ferromagnetic contribution to magnetization, estimated at 10%, might be caused by the presence of ferrimagnetic Fe7Se8, which occupies about 10% of sample volume. From the Andreev spectroscopy we found superconducting energy gap ∆ = 2.6 meV at T = 4.2 K, and from magnetization measurements the critical temperature Tc = 15.8 K. The critical current density in magnetic field H = 4 kOe, determined from magnetization measurements, is jc = (1–2)× 10 A/cm and weakly depends on magnetic field intensity.

Electrophysical properties and the structure of the YBa2Cu3O y compound thermally restored after low-temperature decomposition

The electrophysical properties and structure of the nonstoichiometric high-temperature superconductor YBa2Cu3Oy restored at T = 930–950°C after low-temperature decomposition (T = 200°C) into phases different in the oxygen content have been studied. It has been shown that, unlike heat treatments at T ≤ 900°C, the superconducting properties are almost completely restored for 3–5 h during grain recrystallization, which is impossible at lower temperatures. After short-term annealing at T = 930–950°C (for 1–2 h), the ceramic material still contains a significant number of structural defects, most likely, in cation sublattices. These defects can contribute to the pinning of magnetic vortices, which substantially increases the critical current density in magnetic fields up to 2 T as compared to ceramic materials produced by the conventional technology.

Researches of Structure Formation Peculiarities in the Internal-Tin ${\hbox {Nb}}_{3}{\hbox {Sn}}$ Strands

Addition of manganese in elements of matrix for internal-tin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands has been investigated. Two types of multifilamentary strands with distributed source of tin, 1.8 wt.% Mn in elements of matrix before reaction heat treatment and 1 wt.% Mn in matrix after reaction, have been fabricated by internal-tin method. One of the produced strands had reinforced stabilizer from CuNb nanocomposite alloy. The increase of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn layer growth rate in superconductors filaments of manganese doped strands was determined. Microstructures of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn filaments after reaction heat treatment were investigated by SEM and TEM microscopes. The critical current density in magnetic fields up to 20 T, hysteresis losses, critical temperature and mechanical characteristics were measured. The increase of critical current density in internal-tin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands with manganese doped matrix and the formation of fine microstructure Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn layers was revealed.

Peculiarities of High-Pressure Oxygenation of MT-YBCO

The oxygenation under the high 16 MPa oxygen pressure allows reducing the duration of oxygenation and in the case of thin-walled MT-YBCO ceramics (with drilled holes) leads to a decrease of the amount of macrocracks in the structure and to an increase in critical current density in the ab-planes. An increase in the twin density enhances the critical current density in the ab-planes of the Y123 textured structure of MT-YBCO. After oxygenation under different conditions the MT-YBCO ceramics produced from a mixture of Y123 with Y211 demonstrated a critical current density in magnetic fields above 2 T at 77 K higher in the ab-planes and lower in the perpendicular c-direction than the MT-YBCO produced from Y123 and Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . Mechanical properties (hardness, fracture toughness, Young modulus) have been estimated for various types of MT-YBCO oxygenated under different conditions. Both traditional and thin-walled ceramics have a higher microhardness after oxygenation under high 16 MPa oxygen pressure.

Investigation of the multifilamentary (Nb,Ti)/sub 3/Sn conductors with CuNb reinforced stabilizer

Multifilamentary Nb/sub 3/Sn superconducting wires with Cu stabilizer reinforced by Cu-16% Nb circular layer and with the filaments artificially doped by Ti were developed. Microstructure, mechanical properties, superconducting parameters of (Nb,Ti)/sub 3/Sn wires with round and rectangular cross sections were investigated. The influence of heat treatment regimes on the wires critical current density in magnetic fields up to 14 T was examined. The changes of critical current density under the axial strain at 4.2 K were analyzed and distinct shift for a higher strains without diminishing of the critical current was confirmed. The comparison of obtained results with the appropriate values for the similar wires without Cu-Nb reinforcement was made. It was shown that the ultimate tensile strength and yield strength for the developed wires were higher in a factor of 1.5.

Characterization of YBa2Cu3O7/PrBa2Cu3O7 superlattices

We investigated the structural and superconducting properties ofc-axis oriented (YBa2Cu3O7) nY /(PrBa2Cu3O7) npr superlattices with thicknesses of the individual layers down to one unit cell (10≥nY≥1; 18>nPr≥ 1). By transmission electron microscopy and X-ray diffraction we find an excellent structural quality of the samples, though the quantitative analysis shows the existence of defects. In superlattices with decoupled YBa2Cu3O7 layers of two unit cell thickness we find a highT c value of 75 K. We probed the flux line structure in the superlattices by measurements of the critical current density in magnetic fields. The experiments show that the flux-line dynamics is dominated by the movement of pancake vortices.

Enhancement of critical current density in magnetic field in Ag-clad Bi-Pb-Sr-Ca-Cu-O wire

Conventional processing techniques have been used to achieve significant improvements in the Jc under magnetic field in Ag-clad wires of superconducting Bi-Pb-Sr-Ca-Cu-O. The weak links in the tapes rolled from the wires have been greatly reduced, and an extended plateau regime in the Jc-H curve has been observed. Jc values of 19000 A/cm2 at 77 K and 0 T, 13900 A/cm2 at 77 K and 0.1 T, and 6200 A/cm2 at 77 K and 1 T have been measured. The high density, excellent grain alignment, and high density of dislocations are responsible for the improved flux pinning and concomitant Jc-H characteristics.