YBCO Samples Research Articles

Influence of Ag Doping on Thermal Conductivity and Magnetic Levitation of Single Grain YBCO Superconductors for High-Temperature Superconducting Maglev

Ag doping in (RE)Ba2Cu3O7−δ [(RE)BCO] bulk high-temperature superconductors has been recognized as an effective way to improve the mechanical and superconducting properties of REBCO bulk superconductors for practical applications such as high-temperature superconducting (HTS) Maglev. Ag2O nanoparticles doped YBCO samples with different doping amounts (x, x varies from 0∼0.5 wt%) were fabricated by Top-Seeded Melt-Growth method (TSMG). The samples’ steady-state thermal conductivity (λ) and the magnetic levitation force (FL) were measured by a testing platform under a similar condition to the HTS Maglev system. The effects of Ag2O doping on the λ and FL of single domain YBCO bulks have been systematically studied. The λ of the c-axis and the ab-plane were calculated through the steady-state heat flow method. We observed that λ increases distinctly when x ≥0.3 wt%. The doping amount of 0.3 wt% has been evidenced to be the optimal value, of which the λ of the c-axis and ab-plane are approximately 52% and 48% higher than the undoped one respectively. According to the results of the FL measurement, we found FL will increase while the relaxation rate of the FL will decrease by adding trace amounts of Ag2O nanoparticles in comparison to the undoped sample. This observation suggests that Ag-doping is an effective way to enhance thermal conductivity as well as the superconducting properties of YBCO superconductors for practical applications.

Enhancing pinning ability by the addition of potassium niobate nanorods in YBCO superconductor

In the current study, we have investigated the effect of adding potassium niobate (KNbO3) nanorods (NRs) in YBCO superconductor to improve flux pinning properties. The KNbO3-NRs are synthesized by hydrothermal method, and KNbO3-YBCO nanocomposites are prepared by incorporating variable amounts of the NRs in YBCO matrix by solid-state reaction method. X-ray diffraction (XRD) pattern confirmed the orthorhombic phase of YBCO, KNbO3-NRs, and KNbO3-YBCO nanocomposite samples. The morphology and composition of the YBCO, KNbO3, and KNbO3-YBCO nanocomposites are studied using field emission scanning electron microscopy (FESEM) and energy-dispersive x-ray spectroscopy (EDX). Magnetic measurements of KNbO3-YBCO nanocomposites are carried out at temperatures from 15 to 65 K under an external magnetic field from -7 to + 7 T. The value of critical temperature (TC0) in xKNbO3-YBCO nanocomposites showed no significant decrease from the TC0 value obtained for YBCO, indicating that inserting a modest amount of KNbO3-NRs into the YBCO matrix does not result in substantial changes in TC0. The critical current density (JC) showed an enhancement of ∼ 3.6 times in 0.5wt%KNbO3-YBCO nanocomposite compared to YBCO. Additionally, when the concentration of KNbO3-NRs in YBCO was raised, the critical current density (JC) decreased due to the accumulation of KNbO3-NRs at the interfaces between grain boundaries. The rate of JC decay decreases as the externally applied field increases for nanocomposite samples compared to YBCO, showing an improvement in the pinning properties of nanocomposites.

Near-infrared light-induced superconducting-like state in underdoped YBa2Cu3Oy studied by c -axis terahertz third-harmonic generation

The recent observation of the light-induced superconducting (SC)-like transient response in $c$-axis optical conductivity far above the SC transition temperature ${T}_{\mathrm{c}}$ in underdoped $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ (YBCO) has attracted a great deal of attention in the field of high-${T}_{\mathrm{c}}$ superconductors. Since then, various theoretical and experimental studies have been devoted to elucidating its microscopic origin. One prominent fingerprint of light-induced superconductivity is the emergence of $1/\ensuremath{\omega}$-like spectral behavior in the imaginary part of the optical conductivity in the terahertz (THz) frequency range. However, the spectral profile can also be described by the Drude response of the quasiparticles (QPs) with a substantially low scattering rate. To circumvent this critical ambiguity, we investigated the light-induced nonequilibrium state in an underdoped YBCO sample with ${T}_{\mathrm{c}}$ of 61 K using the nonlinear THz optical response originating from the SC collective excitation of the ac-driven Josephson current. Upon the near-infrared (NIR) photoexcitation above ${T}_{\mathrm{c}}$ in the YBCO sample, the $1/\ensuremath{\omega}$-like spectral behavior in the imaginary part of the optical conductivity emerges, consistent with previous studies. However, the THz third-harmonic generation arising from the ac-driven Josephson current along the $c$-axis was absent in the NIR photoexcited state. These results indicate that the NIR pump-induced state exhibiting the $1/\ensuremath{\omega}$-like response above ${T}_{\mathrm{c}}$ is distinct from the long-range-ordered SC state in equilibrium. Based on these observations, the possible origins of the irregularly coherent charge-carrier response along the $c$-axis induced by photoexcitation are discussed.

The effect of fabrication method on physical properties of different Y211 and 20% Ag2O added YBCO sample

The effect of fabrication method on physical properties of different Y211 and 20% Ag2O added YBCO sample

Effect of the Heat Treatment Applied During the Welding Process on Superconducting Properties of the Welded YBCO Samples

Two Y123 samples labeled as Y1 and Y2 were welded by using a Y123 solder reagent labeled as YA. Y1 and Y2 samples were produced by top seed melt growth (TSMG) method in Y123 + 30 wt.% Y211 composition and YA was produced by melt powder melt growth (MPMG) method in Y123 + 30 wt.% Y211 + 20 wt.% Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O composition. Artificial grain boundaries were created with the solder reagent and a pressure source was used during the welding process to obtain larger bulk superconducting samples. Welded sample was cut horizontally into three slices and these slices were named top down WY1, WY2 and WYA. Some superconducting properties such as superconducting transition temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of the welded samples were investigated before and after the welding process. Good quality welds obtained mechanically and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values determined from the resistivity measurements are around 92 K for all specimens, stating that the welding has no negative effect on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . The calculated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values are 13.71, 12.08 and 9.97 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the Y1, Y2 and YA specimens cut from the samples before welding process while the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values are 2.33, 21.13 and 14.42 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for WY1, WY2 and WYA specimens cut from the welded sample after welding process, respectively. It was observed that the welding process enhanced the superconducting properties of the welding region. After the welding process, the superconducting properties of the high-quality samples oriented in the c-axis decreased less than the samples that do not have a preferential orientation or grain structure.

Defect Evolution in Y&lt;sub&gt;0.5&lt;/sub&gt;Gd&lt;sub&gt;0.5&lt;/sub&gt;Ba&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7-&lt;/sub&gt;&lt;sub&gt;δ&lt;/sub&gt; Layer by H Ion Irradiation

In order to further improve the superconducting current carrying capacity of REBCO coated conductor under strong magnetic field, ion irradiation is used to generate the pinning center of introduced magnetic flux in the REBCO coated conductor. In this paper, the H-ion irradiation of REBCO second generation high temperature superconductor strip was carried out by using the 320kV high charge state ion synthesis research platform. DB-SPBA combined with Raman spectroscopy was used to measure the change of microstructure in YBCO samples irradiated by H+ions within the range of 5.0×10&lt;sup&gt;14&lt;/sup&gt;~1.0×10&lt;sup&gt;16&lt;/sup&gt;. The positron annihilation parameters in YBCO before and after irradiation were analyzed. It is found that after 100 keV H+ion irradiation, a large number of defects including vacancy, vacancy group or dislocation group are produced in the superconducting layer. The larger the irradiation dose, the more vacancy type defects are produced, the more complex the defect types are, and the annihilation mechanism of positrons in the defects changes. Raman spectroscopy results show that with the increase of H+ion irradiation dose, the oxygen atoms in the coating rearrange, the plane spacing increases, the orthogonal phase structure of the coating is destroyed, and the degree of order decreases. The defects produced by such ion irradiation lay a foundation for the introduction of flux pinning centers. Further research can be carried out in combination with X-ray diffractometer, transmission electron microscope, superconductivity and other testing methods to provide theoretical and practical reference for the optimization of material properties.

Controllable rectification on the thermal conductivity of porous YBa2Cu3O7− x superconductors from 3D-printing

Superconducting YBa2Cu3O7−x (YBCO) bulks have promising applications in quasi-permanent magnets, levitation, etc. Recently, a new way of fabricating porous YBCO bulks, named direct-ink-writing (DIW) 3D-printing method, has been reported. In this method, the customized precursor paste and programmable shape are two main advantages. Here, we have put forward a new way to customize the YBCO 3D-printing precursor paste which is doped with Al2O3 nanoparticles to obtain YBCO with higher thermal conductivity. The great rheological properties of precursor paste after being doped with Al2O3 nanoparticles can help the macroscopic YBCO samples with high thermal conductivity fabricated stably with high crystalline and lightweight properties. Test results show that the peak thermal conductivity of Al2O3-doped YBCO can reach twice as much as pure YBCO, which makes a great effort to reduce the quench propagation speed. Based on the microstructure analysis, one can find that the thermal conductivity of Al2O3-doped YBCO has been determined by its components and microstructures. In addition, a macroscopic theoretical model has been proposed to assess the thermal conductivity of different microstructures, whose calculated results take good agreement with the experimental results. Meanwhile, a microstructure with high thermal conductivity has been found. Finally, a macroscopic YBCO bulk with the presented high thermal conductivity microstructure has been fabricated by the Al2O3-doped method. Compared with YBCO fabricated by the traditional 3D-printed, the Al2O3-doped structural YBCO bulks present excellent heat transfer performances. Our customized design of 3D-printing precursor pastes and novel concept of structural design for enhancing the thermal conductivity of YBCO superconducting material can be widely used in other DIW 3D-printing materials.

Casimir energy for N superconducting cavities: a model for the YBCO (GdBCO) sample to be used in the Archimedes experiment

In this paper we study the Casimir energy of a sample made by N cavities, with Ngg 1, across the transition from the metallic to the superconducting phase of the constituting plates. After having characterised the energy for the configuration in which the layers constituting the cavities are made by dielectric and for the configuration in which the layers are made by plasma sheets, we concentrate our analysis on the latter. It represents the final step towards the macroscopical characterisation of a “multi-cavity” (with N large) necessary to fully understand the behaviour of the Casimir energy of a YBCO (or a GdBCO) sample across the transition. Our analysis is especially useful to the Archimedes experiment, aimed at measuring the interaction of the electromagnetic vacuum energy with a gravitational field. To this purpose, we aim at modulating the Casimir energy of a layered structure, the multi-cavity, by inducing a transition from the metallic to the superconducting phase. After having characterised the Casimir energy of such a structure for both the metallic and the superconducting phase, we give an estimate of the modulation of the energy across the transition.

Improved trapped field performance of single grain Y‐Ba‐Cu‐O bulk superconductors containing artificial holes

AbstractThe intrinsic mechanical properties of single‐grain RE‐Ba‐Cu‐O bulk high‐temperature superconductors can be improved by employing a thin‐wall geometry. This is where the samples are melt‐processed with a predefined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin‐wall YBCO disks were determined using the Brazilian test at room temperature. Compared with conventional single grain YBCO disks, the thin‐wall YBCO disks displayed an average tensile strength that is 93% higher when the holes were filled with Stycast epoxy resin. This implies a thin‐wall sample should, in theory, be able to sustain a trapped field that is 39% higher without exceeding the mechanical limit of the sample. High‐field magnetization experiments were performed by applying magnetization fields of up to 11.5 T, specifically to break the samples in order to verify the effect of increased mechanical strength (and improved cooling) on the ability of bulk (RE)BCO to trap field successfully. The standard YBCO sample failed when it was magnetized with a field of 10 T at 35 K, suffering permanent damage. As a result, the standard sample could only trap a maximum surface field of 7.6 T without failure. On the other hand, the thin‐wall YBCO sample survived all magnetization cycles, including a maximum magnetization field of 11.5 T at 35 K, demonstrating a greater intrinsic ability to withstand significantly higher electromagnetic stresses. By subsequently field‐cooling the thin‐wall sample with 11 T at 30 K, a surface field of 8.8 T was trapped successfully without requiring any external ring reinforcement.

Enhanced flux pinning properties of NaNbO3 nanorods added YBCO composite superconductor

In this work, sodium niobate (NaNbO3) nanorods (NR) – YBCO superconductor composites with different wt% (0–2%) of NaNbO3 were prepared via a two-step process of hydrothermal and solid-state reaction, and its structural, electrical, and magnetic characterizations were carried out. XRD studies revealed that the orthorhombicity of YBCO is preserved in all nanocomposite samples. The superconducting transition temperature decreases from 92 K to 90.5 K when the addition of NaNbO3 was increased to 2 wt%. Magnetization studies revealed a significant increase of critical current (Jc) and pinning force (Fp) in the NaNbO3 (NR) added YBCO sample which has been attributed to the creation of artificial pinning centers due to the presence of NaNbO3 NR. For the 0.5 wt% nanorods added sample, the enhancement in Jc and Fp was maximum. Temperature and field dependence of Jc were carried out to probe the nature of pinning in the nanocomposite superconductors.

A comparative study of (Ce) and (Gd) doping influence on the superconducting properties of YBCO ceramics

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa2-xRExCu3O7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature TC and the critical current density JC.The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa2-xRExCu3O7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature TC was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of TC for YBa2-xRExCu3O7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density JC was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.

Employment of NdBCO/YBCO/MgO film seed in the infiltration growth technique for fabricating single-grain YBCO bulk superconductors

The quality of the seed is a key factor for growing well c-axis oriented RE–Ba–Cu–O (REBCO) single-grain superconductors. In this study, the commercial NdBCO/YBCO/MgO film (300 nm NdBCO with 20 nm YBCO buffer layer on MgO substrate) is employed as seed in the infiltration growth (IG) method for growing YBCO single grains, including the conventional 211-IG and the novel 011-IG techniques. And an embedded seed mode was used for preventing the movement of the thin film during heat treatment process in the 011-IG technique. The results indicate that, YBCO single grains have been successfully grown via the seeding of NdBCO/YBCO/MgO film in the two IG processes, which proves the feasibility of the film seed in the IG method. Four strictly perpendicular growth sector boundaries on the top surface of the samples and clear (0 0 l) diffraction peaks in the X-ray diffraction (XRD) results both indicate the high c-axis orientation and well growth quality of the samples, which proves the excellent performance of the NdBCO/YBCO/MgO film seed in the IG method. Superconducting property measurement showed that, the 011-IG YBCO sample exhibited enhanced levitation force and Jc properties than the 211-IG sample.

Use of Bulk Superconductors in the Excitation System of Low-Speed Synchronous Generators

This work focuses on implementing HTS bulks in the excitation circuit of low-speed synchronous generators as permanent magnets. In addition to the implementation study, it is also addressed to remagnetize HTS bulks in electric generators. To reduce the maintenance costs and time required for the magnetization process, an in-loco remagnetization is used. The HTS bulks are magnetized in their position inside the machine's magnetic circuit. A pulse-field magnetization (PFM) technique is used, using the stator coils of a linear generator. YBCO and GdBCO samples are tested. The experimental procedure starts with the in-loco PFM to magnetize the HTS bulks and, by applying an oscillatory movement to the linear generator's moving part, measuring the magnetic flux density induced voltage is done. Experimental tests show that, for the FeSi core used in the generator, the YBCO material is most suitable for the excitation circuit.

Prediction of f−wave pairing symmetry in YBa2Cu3O6+x cuprates

We perform a numerical simulation of a three-band Hubbard model with two CuO$_2$ planes and a single CuO chain layer for YBCO cuprates. The spin-fluctuation mediated pairing interaction is computed within the multiband random-phase approximation, and its pairing eigenvalues and eigenfunctions are solved as a function of chain state filling factor $n_c$. We find that for the intrinsic value of $n_c$ in YBCO samples, one obtains the usual $d$-wave pairing symmetry. However, if we dope the chain layers with holes, while keeping the plane states doping fixed, the leading pairing symmetry solution becomes an unconventional $f$-wave symmetry. The mechanism behind the $f$-wave pairing is the competition between the plane states antiferromagnetic nesting and chain states' uniaxial nesting. We also find that the pairing strength is strongly augmented when the flat band bottom of the chain state passes the Fermi level for a fixed plane states doping. The $f$-wave pairing symmetry can be realized in YBCO cuprates in future experiments where the self-doping mechanism between the chain and plane states can be minimized so that only chain state can be selectively hole doped.

High frequency vortex dynamics in YBa2Cu3O7−x with Ba2YTaO6-Ba2YNbO6 nanodefects

We studied pinning characteristics of YBa2Cu3O7−x (YBCO) with 5 mol.% Ba2YTaO6/Ba2YNbO6 (BYNTO). In contrast to widely used d.c methods, at microwaves very short oscillations of the fluxons are involved giving the information on both the pinning strength, through the pinning constant and on dissipation, related to the vortex core physics, through the viscosity η. We estimate the pinning constant kp , the vortex viscosity η and also the maximum creep factor χmax. The results were compared not only with the pristine YBCO sample but also with the effect of another type of columnar defects (BZO) in YBCO. All film samples were grown by Pulsed Laser Deposition (PLD) technique at nearly the same conditions to ensure the uniform. We detect an improvement of all pinning characteristics of YBCO-BYNTO sample in the temperature range 62 - 90 K and for field up to 0.75 T. While the average diameter of the defects is similar for YBCO-BYNTO and YBCO-BZO the key of the superior characteristics in YBCO-BYNTO could be both the concentration of columns and an addition of another phase of point-like defects.

Comparison of the Effect of Graphene and Graphene Oxide Doping on YBCO

Weak-links in high temperature superconductors (HTS) are a result of an incorrect stoichiometric ratio found in grain boundaries and misaligned planes. These weak-links severely decrease the critical transport current of the bulk HTS material (such as YBCO) and increase resistance in the normal state. Bulk YBCO was doped with graphene oxide (GO) and reduced graphene oxide (rGO) in the following dopant concentrations: 0, 0.1, 0.5, 0.7, 0.9 and 1 % wt. Through mechanical hardness testing, it was observed that the hardness of the samples increased as the GO and rGO concentration increased. The 1 % wt. doped GO and rGO samples was observed to be hardest, with a true hardness of 2.630 GPa and 2.405 GPa respectively, compared to the control sample with a true hardness of 1.499 GPa. Critical transition temperature (TC ) of the GO doped YBCO samples are greater than rGO doped samples and is presumably related to the higher oxygen content found in GO. The 0.7 % wt. doping for GO and rGO samples had the highest critical transition temperature of 98 K and 91 K, respectively. Both GO and rGO samples showed a decrease in normal resistance up to 0.7 % wt. doping, compared to the control sample. The weak-link effect was most improved in the 0.7 % wt. doped samples for GO and rGO.

Enhanced superconducting properties of multi-wall carbon nanotubes added YBCO-123 Superconducting System

We investigated multi-wall carbon nanotubes (MWCNT’s) adding in Y1Ba2Cu3Ox high temperature superconductor system. We used solid-state method for sample preparation and 0.0 < x < 5.0 wt% MWCNT’s were added to the main matrix. Structural evolution, electrical transport and magnetic properties of material produced was investigated. According to the results obtained the superconducting onset temperature, Tconset, was not changed excessively, however, it was observed that the transport critical current density, Jctran, increased by at least 6-fold compared with the pure YBCO samples. Magnetic properties of material were also investigated by means of magnetization measurements up to 9 T together with the I–V measurements and pinning force, Fp, calculations.

The effect of APC/YBCO interface on the angular range of effective pinning by one-dimensional artificial pinning centers in YBa2Cu3O7-x nanocomposite films

The APC/YBCO interface has been reported to directly affect the pinning efficiency of 1D APCs at B//c-axis. This raises a question on how the APC/YBCO interface affects angular range of the pinning effectiveness for a given 1D APC. In this work, two types of 1D APCs of different APC/YBCO interfaces and hence pinning efficiencies were selected to understand the correlation of the pinning efficiency at B//c-axis and the angular range of the effectiveness. Specifically, BaZrO3 (BZO) and BaHfO3 (BHO) 1D APCs were selected for a comparative study in the APC/YBCO nanocomposite films. The BZO and BHO 1D APCs have comparable diameters in the range of 5-6 nm. In the doping range of 2-6 vol.%, both BZO and BHO form c-axis aligned 1D APCs in YBCO films. However, differences are present at their interfaces with YBCO. While the BZO/YBCO interface is semi-coherent, a coherent BHO/YBCO interface has been found to be critical to the higher pinning efficiency of the BHO 1D APCs. Therefore, they provide ideal systems for investigation of the angular range of pinning effectiveness by 1D APCs. By evaluating the nanocomposites’ maximum pinning force density (Fp, max ) and its location Bmax , normalized to that of the reference YBCO film as functions of magnetic field (B) orientation at temperatures of 65–77 K, a quantitative correlation between the pinning efficiency of the BZO 1D-APCs and their effective angular range was obtained. Our results indicate that all 1D APCs can provide enhanced Bmax over certain angular ranges away from the c-axis. However, 1D APCs with higher pinning efficiency, such as BHO 1D APCs can have enhanced Fp, max over the entire angular range of B-orientations at temperatures of 65-77 K with respect to that for the reference YBCO sample.

Secondary phase particles in bulk, infiltration-growth processed YBCO investigated by transmission Kikuchi diffraction and TEM

We present results of the first application of the transmission Kikuchi diffraction (TKD) technique to bulk, infiltration growth (IG)-processed YBa2Cu3O7−δ (YBCO) superconductors with embedded Y2BaCuO5(Y-211) nanoparticles. By means of focused ion-beam (FIB) milling, TEM slices were prepared from mechanically polished surfaces of bulk, IG-processed YBCO samples. The required optical transparency was reached by additional polishing the resulting surfaces using the FIB and Ar-ion milling. For TKD, the sample was mounted on a homebuilt sample holder in the SEM, which provides the required inclination for TKD. The improved spatial resolution of TKD enabled the investigation of the small Y-211 particles (diameter of about 60–210 nm) embedded in the superconducting YBCO matrix. The fabricated TEM slices further enable the application of transmission electron microscopy to the same sample sections. These tiny Y-211 particles embedded within the YBCO matrix are, together with their strain fields, directly responsible for the high irreversibility fields due to the effective flux pinning of the IG-processed samples.

Influence of NiFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; nanoparticle doping on properties of single-domain YBCO bulk superconductors

NiFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; (NFO) nanoparticle doped YBCO bulk superconductors are fabricated by using a novel top-seed infiltration growth (TSIG) technique. The growth morphology, microstructure and superconducting properties are investigated. The results show that at low doping levels, the normal growth of YBCO single domain is not affected by the NFO doping, but at high doping levels, obvious random nucleation appears at the edge of the sample. The measurement of levitation force indicates that the maximum levitation force on the sample first increases and then decreases with the increase of the NFO doping amount, and the largest levitation force is obtained to be 33.93 N for the sample with a doping level of 0.2% (weight percent). Low-temperature magnetization measurement shows that the YBCO sample exhibits that &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value decreases with NFO amount increasing, and the superconducting transition width (Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;) also broadens gradually. The sample with the optimal doping (0.2% weight percent) presents an enhanced zero-field &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value of 8.68 × 10&lt;sup&gt;4&lt;/sup&gt; A/cm&lt;sup&gt;2&lt;/sup&gt;, which is 31% higher than the sample without dopant. In addition, a more obvious secondary peak of 4.37 × 10&lt;sup&gt;4&lt;/sup&gt; A/cm&lt;sup&gt;2&lt;/sup&gt; at a field of 1 T is observed for the 0.2 wt.% NFO doped sample, which indicates the existence of enhanced &lt;italic/&gt;δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; pinning in the bulk. The SEM measurement shows that two types of particles are trapped in the Y-123 matrix for YBCO sample doped with 0.2% weight percent NFO: one is the large particle with a size mainly ranging from 0.5 μm to 2.0 μm, and the other is small nano-inclusion mainly ranging from dozens of nanometers to about several hundreds of nanometers. Such a microstructure is very similar to the microstructure of the undoped sample we reported earlier. So whether the NFO nanoparticles exist in the microstructure cannot be judged just from the morphology of the nano-inclusions. The electron probe microarea analysis (EPMA) result shows that different concentration distributions of Ni and Fe elements are observed in the sample doped with 0.2% weight percent NFO, which indicates the separation of NFO nanoparticles in the heat treatment process, and the dissolved Ni and Fe ions finally exist in the form of element substitutions in the YBCO bulk. Such element substitutions can introduce local lattice distortions and weak-superconducting regions into the superconducting matrix, which can act as effective flux pinning centers, and hence improving the properties of the samples.