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We report on top-seeded melt growth of GdBa2Cu3O7-δ (GdBCO) bulks added by sharp edged Gd2BaCuO5 nanoparticles (Gd211U) refined by ultrasonication. GdBCO bulks mixed with 30 mol.% of Gd211U were examined to be grown isothermally at different temperatures in a range of 1015 °C−1035 °C using a top-seeded melt growth technique. Magnetic susceptibility measurements show that all samples become superconducting and especially samples grown at 1020°C and 1025°C have a maximum superconducting transition temperature (T c) of 94.5 K. The critical current density (J c) obtained from magnetic hysteresis loops for magnetic fields parallel to the c-axis is up to 65100 A/cm2 (the self-field at 77 K) for a sample grown at 1025 °C, while J c of a GdBCO bulk with conventional Gd211 particles grown at 1025 °C for comparison is 29000 A/cm2 (the self-field at 77 K).

The enhancement of a critical current density (J c) of REBa2Cu3O7-δ (REBCO/YBCO, where RE=rare earth elements and Y) bulk superconductors can be achieved via dispersing normal-conductive RE2BaCuO5 (Y211) particles and other defects which are of nano-metric size in the superconducting matrix. Recently, we demonstrated the integration of high-energy ultrasonic irradiation for fabricating high quality YBCO superconductors which effectively improved J c and trapped fields. In the present work, we investigated the effect of 30 mol.% of Y211 particle produced via high-energy ultrasonication irradiation on the growth and superconducting properties of top-seeded melt grown bulk YBCO single grains. Ultrasonic power of 450 W was employed for 30 minutes to create the sharp-edged, individual and nano-meter sized Y211 phase particles. Systematic isothermal experiments were conducted at various temperatures from 1005 °C − 980 °C. The growth of YBCO grain from a single crystalline NdBCO seed was initiated at 1000 °C and as the isothermal temperature decreased the growth area increased due to the improved peritectic reaction. The field dependence of J c was improved when the under-cooling isothermal temperature decreased. The present method is reliable, cost-effective, and free from any chemical contamination.

International audience; Mg-B superconducting bulk materials are characterized as simple and uniform metallic compounds, and capable of trapping homogeneous field with beautiful conical shapes. Although pulsed-field magnetization technique (PFM) is expected as a cheap and an easy way to activate them, the heat generation due to magnetic flux motion in bulk magnets causes serious degradation of captured fields. It is important to suppress the flux motions during PFM to decrease the heat generation. In this study, authors precisely estimated the flux trapping to the bulk samples, found that the flux-shielding effect related to the sample dimensions. Moreover, the Ti-addition to the bulk sample affected the frequency of flux jump happenings. The magnetic field capturing of 5.0wt%Ti-added samples reached the highest value of 0.76 T, while the starting point of magnetic field invasion into the sample centre shifted from 1.0 T to 1.2 T with increasing sample thickness from 3.67 mm to 5.80 mm. The occurrence of flux jumps was suppressed in 5.0wt%Ti-dopped sample, which means that the heat capacity of the compounds shifted with varying Ti addition, effectively prevented the flux jumps.

Bulk superconductors can trap high magnetic fields exceeding that of conventional permanent magnets as a manifestation of a macroscopic quantum effect. In recent years, a new record trapped magnetic field has been achieved, and the applicability to various devices has been vigorously studied. In this review, the trends in the research and development of superconducting bulk materials, including flux pinning control and mechanical reinforcement for REBCO, magnetization techniques, new materials (MgB₂ and IBSC), and modeling and simulation, are summarized.

The five-year national project in Japan for RD a high in-field minimum Ic value over 54A/cm-width under 3T at 77K was realized in a 200m long EuBCO tape with artificial pinning centers of BaHfO3 by the pulsed laser deposition (PLD) technique on the IBAD template. On the other hand, the AC loss reduction was confirmed in the tapes fabricated by both PLD and the metal organic deposition (MOD) techniques by scribing 100m tapes into 10-filamments. Additionally, the mechanism of the delamination phenomenon was systematically investigated and the strength was improved by eliminating the origins of the weak points in the films. Through the development, all targeted goals were accomplished and the several results were appreciated as a world champion data.

Recent progress in development of RE1Ba2Cu3Ox (REBCO, RE: Y and Rare Earth) coated conductors has been remarkable, which makes practical applications realistic. Considering the major applications, long coated conductors are expected to be used as coils. Improvement of delamination strength throughout the long tape is important issue as well to meet the requirements of those applications. Effect of processing on delamination strength was analyzed in this work. The delamination strength can be distinguished into 3 groups depending on the origins of delamination; weak strength (50MPa) was realized by elimination of those defects which can be controlled by optimization of the process. Statistical analysis showed the improved process gives only one weak spot per thousands of kilometers long tape. The improvement of processing was effective to obtain high delamination strength throughout long wires.

We have studied delamination behavior of GdBa2Cu3O7-d (Gd123) coated conductors fabricated by pulsed laser deposition. Two kinds of delamination tests, transverse tensile test and four points bending test, were performed. The delamination strength of 8 and 4–7 MPa was obtained by transverse tensile test, and interfacial cohesive energy of 7.1 and 5.9 J/m2 was obtained by four points bending test for samples fabricated with different processing rates, 20 m/h and 60 m/h, respectively. EPMA and XPS analyses of delaminated surfaces showed that the weakest position in Gd123 coated conductor was inside of Gd123 layer a few nm apart from Gd123/CeO2 interface. The samples exhibiting a lower interfacial energy had a large gradient in oxygen distribution at the interface. The reason why the delamination occurred there is due to strain concentration induced from both lattice mismatch and inhomogeneous oxygen distribution at the interface.

Combining scanning Hall-probe microscopy (SHPM) with finite element method (FEM), we have investigated three-dimensional current distribution at a silver diffusion joint of RE-123 coated conductor (CC). This research aims at the understanding of electromagnetic behaviors in a jointed CC and at the establishment of an analysis model for it. Two-dimensional distribution of sheet current density in a jointed sample was visualized by a SHPM measurement with a spatial resolution of a few hundred micrometers. Then, it was found that such a distribution included information about current transfer between the jointed pieces. Furthermore, the experimental results were successfully reconstructed by a three-dimensional FEM analysis. We believe that these will be very important findings for the establishment of jointing processes on CCs and for the designs of practical applications which need such processes.

Stable levitation or suspension of a heavy object in mid-air can be realized using a combination of a permanent magnet and a bulk superconductor with high critical current density, in that the force density has reached 100 kN/m 2 . The superconducting flywheel system for energy storage is attractive due to a great reduction in the rotational loss of the bearings. So long as a permanent magnet is used as a magnetic source, however, the electromagnetic force (EMF) is essentially limited by its field strength. In order to overcome such a limitation, we employed a superconducting coil/magnet as a magnetic source and studied the EMF characteristics of bulk superconductors in high-magnetic fields. We also measured the EMF between a bulk superconductor and a specially designed superconducting coil having a high field gradient, and confirmed that the EMF reached 9450 N (force density: 2507 kN/m 2 ).

Flux pinning in melt-processed (Nd 0.33 Eu 0.33 Gd 0.33 )Ba 2 Cu 3 O y "NEG-123" + 35 mol% Gd 2 BaCuO 5 "NEG-211" (70 nm in size) composite doped by Ti0 3 , Mo0 3 and Nb 2 O 5 achieved record values. The optimum values of all three dopands were found to be around 0.1 mol%. Transmission electron microscope (TEM) analysis found clouds of

The GdBaCuO superconducting bulk with stronger pinning characteristics (B T = 1.8 T at 77 K by the field cooled magnetization (FCM)) has been magnetized at T s = 70 - 20 K by the pulsed field magnetization (PFM) techniques; a sequential pulsed-field application (SPA) and a modified multi pulse technique with stepwise cooling (MMPSC). With decreasing T s, the pinning force F p increases especially at the growth sector boundaries (GSBs), and then the nonuniformity of the trapped field profile becomes more and more conspicuous on the bulk surface. At low T s, the SPA technique is not necessarily a suitable technique to enhance the trapped field B T and the total trapped flux Phi T. However, these values can be enhanced by the MMPSC method. The properties of the bulk with stronger pinning characteristics during PFM are discussed.

The high-temperature superconductor (HTS) bulk current lead (BCL) is a crucial device for a large number of current applications such as the propulsion motor with HTS winding. The coexistence of low thermal conductivity and superconductivity enables us to shrink the dimension of the power system. To use the BCL effectively, we have to optimize the temperature gradient across the BCL along its length. For this purpose, it is essential to obtain a better physical contact between the bulk HTS surface and Cu terminal leads. There are, however, many pores at the surface of the bulk which cause difficulties for joining. In order to solve this problem, we focused on an impregnation technique which has been known to improve strength and thermal characteristics of the bulk HTS itself by using epoxy. We succeeded to fill in the pores of the bulk HTS surface with a metal alloy impregnation. Following this method, we made the BCL of Gd-Ba-Cu-O by ourselves. By adopting a suitable cooling with a GM cryocooler, the resistance of the BCL was 0.8 muOmega across the BCL under a current flow of 300 A, considering one end was at 40 K and the other one was at 70 K. The properties of the present BCL are satisfactory for connecting a coil in large current power systems such as superconducting motors.

The driving characteristic of a conveyor with superconducting magnetic levitation is reported. A superconductor (Gd–Ba–Cu–O, Sintered plate) is used to levitate a slider on the surface of a superconductor. In this paper, magneto impedance sensors are used to detect the position of a levitated slider whose size is 7.2 mm square and 2 mm in thickness. This magneto impedance sensor is commercially available and works based on a linear relation between the external magnetic field and the output voltage. This paper describes the results of (1) two-dimensional stepping actuation to arbitrary positions with the step size of 1.2 mm, (2) the maximum conveyance speed of 104 mm/s and (3) successful position feedback control.

We have investigated the fabrication and the superconducting and field trapping properties of large melt-textured Eu–Ba–Cu–O bulk superconductors for the purpose of application as a compact NMR magnet. We successfully fabricated c -axis oriented single-grain bulk samples up to 65 mm in diameter by melt-processing under a low oxygen partial pressure. The samples of 33 and 47 mm diameters could trap magnetic fields of 1.4 and 1.7 T at 77 K, respectively. The position dependence of T c in the sample of 33mm diameter is very small throughout the sample. In 65 mm-sized sample, however, T c and J c lowered in inner region of the sample, leading to lowering of maximum trapped field. Trapped magnetic field was improved with keeping for long time at maximum temperature in melt-processing.

Single grain, Ag-doped Y–Ba–Cu–O bulk superconductors of up to 30 mm in diameter have been fabricated successfully by a seeded infiltration and growth (IG) technique. These samples exhibit low porosity compared with samples grown by conventional top seeded melt growth (TSMG). The density of voids within as-processed IG samples can be reduced further by adding metallic Ag, rather than Ag2O, to the Y2BaCuO5 (Y-211) pre-form. An inhomogeneous distribution of Y-211 has been observed in these samples. Finally, a maximum trapped magnetic field of 0.5 T was observed for Ag-doped Y–Ba–Cu–O of diameter 30 mm at liquid nitrogen temperature (77 K).

We have studied the levitation force of a Gd–Ba–Cu–O bulk superconductor 60 mm in diameter and 20 mm in thickness with a newly developed superconducting magnet system that can provide high field gradient. The magnet system was composed of two superconducting coils that are co-axially placed, and currents are passed in the opposite direction. To study the effect of radial and vertical magnetic field components on the levitation force and its time relaxation, the superconductor was placed at several locations. It was confirmed that the levitation force is strongly dependent on the radial component of magnetic fields. It was also found that the time relaxation was reduced without sacrificing the levitation force by increasing the radial component of the external field.

We succeeded in repairing YBCO coated conductors with local damage using the diffusion joint technique of stabilizing silver layers. A short piece of YBCO coated conductor was put on the damaged part in a face to face manner and joined by the diffusion technique. We also succeed in joining two multi-filament YBCO coated conductors (MFCCs) using the diffusion joint process. After the joint process, Ic was not reduced in any filament, resistance of the joint was low and practically constant in all the joined filaments, and resistance between two adjacent filaments was high enough.

A persistent current switch (PCS) is used for various superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of Y–Ba–Cu–O (YBCO) bulk as a PCS. In previous study, in order to investigate the contact characteristics of the switch, 50 A current test was performed and the contact resistance between two contacts was measured by four terminal method. As a result, it became clear that polishing and metal depositing on YBCO surface was effective to reduce the residual resistance, and the authors achieved to reduce this resistance to 0.27 μΩ, which was less than our target value of 1 μΩ. At the same time, the greater current test (above 50 A) was performed in order to examine the transition to normal conductive state in the YBCO contacts. As a result, it could be found that the current value when a local quench occurred (local quenching current: LQC) had a strong relationship with the layer thickness of deposited silver on YBCO surface. This paper focused on the relationship between the transition current to the normal conductive state in the YBCO (quenching current) and the layer thickness of deposited silver on YBCO surface. And it was also observed whether the number of current cycles affected the value of quenching current.

We have developed a low-cost, short time manufacturing process using a novel method, starting from a mixture of Er2BaO4, BaCuO2, and CuO, with an excess of Er at expense of Ba. Several micrometers thick films were prepared by the screen-printing technique, spreading the mixture paste on silver substrates, processed then in Ar–1% O2 atmosphere. Using a double-step annealing process, we obtained good quality Er-123 thick films on silver substrates, with Tc (onset) 92 K. Formation of large flat grains was observed by scanning electron microscope. According to XRD analysis, the films were preferentially c-axis oriented. The magnetic (induced), self-field Jc measured at 77 K was above 32 kA/cm2. We observed a strong dependence of the transport current, Ic, on the grain size. The maximum Ic at 77 K as high as 10 A was observed in the sample with the average grain size around 40 μm. The present results indicate that our technology, enabling preparation of large-area superconducting thick films on Ag-based substrates in short processing times, is relatively cheap and appropriate for utilization in long-length RE-123 silver sheath wire production for commercial applications.

Stable levitation or suspension of a heavy object in mid-air can be realized using a combination of a permanent magnet and a bulk superconductor with high critical current density, in that the force density has reached 100 kN/m2. The superconducting flywheel system for energy storage is attractive due to a great reduction in the rotational loss of the bearings So long as a permanent magnet is used as a magnetic source, however, the electromagnetic force (EMF) is essentially limited by its field strength. In order to overcome such a limitation, we employed a superconducting coil/magnet as a magnetic source and studied the EMF characteristics of bulk superconductors in high magnetic fields. We also measured the EMF between a bulk superconductor and a specially designed superconducting coil having a high field gradient, and confirmed that the EMF reached 9,000 N (force density: 1,190 k N/m2).

Diffusion joint processes using Ag stabilizing layer for YBCO tape were performed in varied parameter such as temperature, time duration, cooling procedure and conditions of surface for Ag stabilizing layer to optimize for joint condition. We succeeded in developing a brief process with which low resistance below 5 × 10−13 Ω m2 at the joint without any degradation of Ic was achieved by polishing surface of Ag stabilizing layer and quenching procedure. The polishing is effective in reducing joint time and temperature. The mechanism was discussed for the decrease in Ic after joint held at 873 K.

We studied the effects of magnetic field and the temperature on the levitation force for a bulk Gd–Ba–Cu–O superconductor 60 mm in diameter and 20 mm in thickness. Magnetic field distribution in the bulk body was monitored with Hall sensors placed on the sample surface. The sample was placed 10 mm below the magnetic center of a superconducting solenoid coil. The sample was cooled in zero-field mode, and the magnetic field was increased from 0 to 5 T. Therefore, the levitation force which acts downward was measured at various temperatures. After measuring the levitation force, its time relaxation was also measured for 1 h while applying 5 T. The levitation force could be increased with increasing magnetic field in all the temperature range. Lowering temperature was effective in increasing the levitation force and reducing its time relaxation.

With the aim to develop low cost, high performance superconducting thick films, we tested a new method, starting from a mixture of Er 2 BaO 4 , BaCuO 2 , and CuO in the stoichiometric Er-123 ratio. Thick films were prepared by the screen printing technique, spreading the mixture paste on silver and MgO single-crystalline substrates processed then in Ar-1% O 2 atmosphere. Using a double-step annealing process, we obtained good quality Er-123 thick films on silver substrates, with T c (onset) 92 K and transition width

A new concept of synchrotron radiation (SR) sources with ring-shaped high-Tc superconducting bulk (bulk ring) magnets have been proposed at the SPring-8, a SR facility in Japan. During the proof-of-principle experiments, it was found that the magnetic field generated by the bulk ring gradually decreased, due to mechanical damages in the bulk ring. In order to improve the mechanical property of the bulk ring toward realization of this concept, two methods of reinforcement, i.e., resin impregnation and iron ribbing, were proposed. The effects of these methods were investigated with four bulk ring samples and it was found that combination of the two methods significantly improved the mechanical property.

The thermodynamic stability of MgO-doped Nd 1+ x Ba 2− x Cu 3 O y ( x = 0–0.5) has been investigated as a function of solid solution level ( x ) under various oxygen partial pressures for use as a seed crystal composition in the melt growth of (LRE)-Ba–Cu–O (where LRE = light rare earth) bulk superconductors. The gradient of decomposition temperature, T p , against solid solution level increases significantly with decreasing oxygen partial pressure, indicating that MgO-doped Nd–Ba–Cu–O (NdBCO) seed crystals should be grown under reduced p O 2 to obtain seeds with high T p . Based on these results, the optimum cold-seeded processing conditions for the fabrication of single grain GdBCO bulk superconductors containing silver (GdBCO/Ag) under a controlled oxygen partial pressure of 0.01 atm have been determined. The onset T c of GdBCO/Ag samples grown in air with the optimized seed crystal composition is improved significantly with increasing Ag content, indicating that silver addition to the precursor powder suppresses the formation of Gd–Ba solid solution.

We have studied the magnetic field distribution of the stacked two single domain Gd–Ba–Cu–O large bulk superconductors exceeding 140 mm in diameter, and compared with the distribution of one single domain bulk. The maximum trapped magnetic field of the stacked bulk at 65 K was 4.3 T and 5 T at the surface and at the center of two large bulks respectively, when the bulks were field-cooled in 5 T. It was found that the magnetic field could reach a longer distance and wider area by increasing the thickness. Therefore, larger and thicker bulk superconductor shows several benefits in terms of practical applications.

A persistent current switch (PCS) is used for superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of YBCO bulk as a mechanical PCS. This paper focused on the current carrying area (called a-spot ) on contact interfaces and presented an effect of interface condition on electrical contact characteristics in order to clarify the contact mechanism. The authors prepared various samples with different surface treatments (roughness and washing), and measured the contact voltage with a four-terminal method. YBCO deposited with metal (silver and indium) layer samples were similarly subjected to the contact voltage measurements. It was found that the contact interface conditions strongly affect the contact characteristics.

A persistent current switch (PCS) is used for superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of Y–Ba–Cu–O (YBCO) bulk as a mechanical PCS. In previous study, in order to investigate the contact characteristics of switch, 50 A current test was performed and the contact resistance between two contacts was measured by four-terminal method. As a result, it became clear that polishing and metal depositing on contact surfaces was effective methods to reduce the residual resistance. This paper focused on the greater current test (above 50 A) in order to perform more practical experiment as PCS used for SMES. In this experiment, the authors examined the characteristics to the transfer current of switch, which was not obtained by former 50 A current test. As a result, it was obtained that the transfer current had a relationship with the layer thickness of deposited Ag on contact surfaces.

On the processing melt-textured RE–Ba–Cu–O bulk superconductors, we investigated the formation of defects in green bodies during powder compression process and the effect of the defects on the final bulk products. Two kinds of Y–Ba–Cu–O powders with fine and large particle sizes and the granules of binder-added fine powder were uniaxially pressed into tablets (20 mm in diameter) under different pressures from 31 to 125 MPa. When the fine powder was pressed at pressures above 62 MPa, several defects such as lamination, capping and vertical cracking were found in green bodies. The defects in green bodies partially remained after melt-processing and lowered the field-trapping abilities of melt-textured bulk samples. The addition of organic binder is very effective method to reduce the defects in green bodies.

We, respectively, fabricated GdBa2Cu3O7−δ (Gd123) single domain superconductors by melt growth process in air with Gd2Ba4CuZrOx (GdZr2411) and nanosize ZrO2 dopants. The microstructures and superconducting properties were investigated by scanning/transmission electron microscopy (SEM/TEM) and SQUID. GdZr2411 and BaZrO3 particles with the average size of 50 nm were observed in the GdZr2411 and nanosize ZrO2 doped Gd123 bulks by TEM, respectively. Critical current density (Jc) was enhanced up to 100,000 A/cm2 at 77 K and self-field with 0.4 mol% nano-sized ZrO2. The present study also showed that small amount GdZr2411 dopants (8 mol%, ratio to Gd123) were effective to induce a δTc-type pinning.

We have studied magnetic properties of a single grain Gd–Ba–Cu–O bulk superconductor 140 mm in diameter. The distribution of the trapped magnetic field showed that the sample was a single domain without serious weak links. The maximum trapped magnetic field at 65 K was 3.66 T, when the bulk was field-cooled in 4 T. From the distribution measurements of the trapped magnetic field, it was confirmed that a large amount of flux could be trapped in a large grain superconductor. In addition, the magnetic field could reach a longer distance in a large bulk compared to smaller samples. The repulsive force measurements also showed that the repulsive force density of the larger bulk was much larger than those of smaller samples.

High-temperature superconductors (HTS) have high potential for various engineering applications such as a superconducting flywheel energy storage system. The attractive feature of the superconducting magnetic bearings in the energy storage system is a reduction in the rotational loss. In this study, we studied the feasibility of a superconducting magnet to support bulk superconductors in magnetic bearings with the aim of increasing the stored energy. The superconducting magnet has a room temperature bore of 100 mm with the maximum magnetic field of 3.5 T. In addition, we used a GM freezer (10 K in the lowest attainment temperature), which can control the temperature of the bulk superconductors. The used bulk samples were Y-Ba-Cu-O and Sm-Ba-Cu-O 46 mm in diameter and 15 mm in thickness fabricated with a top-seeded melt-growth process. We have studied the effects of the temperature and magnetic field on the levitation force and its time relaxation. The levitation forces were measured by applying the magnetic fields of 0-2 T at 10-77.3 K. It was found that the levitation force increased with lowering temperature in both samples. The time relaxation of the levitation force was also reduced with lowering temperature. Sm-Ba-Cu-O exhibited better performance in the levitation force and its time relaxation in a high temperature and high-field region.

Bulk GdBa2Cu3O7-delta (Gd123) superconductors were fabricated in air by adding ZrO2/SnO2 nanoparticles with an average size of 50 nm. The effect of addition on microstructure and superconducting properties was investigated by scanning electron microscopy (SEM)/transmission electron microscopy (TEM) and SQUID. SEM results show that the distribution of Gd2BaCuO5 (Gd211) particles is inhomogeneous around the seeding site of single domain, induced by the addition of nano-par- ticles. Particles with size less than 50 nm were observed by TEM inside Gd123 single domain, while the typical size of fined Gd211 particles is about 100 nm. Critical current density (Jc) was enhanced by the proper amount addition of ZrO2/SnO2 additions. The highest Jc of 100,000 A/cm was presently achieved in the bulk with 0.4 mol % ZrO2, under self-field at 77 K. Excess amount addition rather suppresses superconducting properties. The optimum addition amount is 0.2-0.8 mol % for ZrO2and 0.4-0.8 mol % for SnO2 , ratio to Gd123, respectively.

Single domain GdBa2Cu7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed Gd123 was successfully enhanced by addition of both BaCO3 and BaCuO2−x, which suppress the formation of Gd1+xBa2−xCu3O7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO3 and 0.05 to 0.1, M BaCuO2−x per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band formed by Gd2BaCuO5 particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and 8, mm in thickness and a high critical current density Jc up to 91,200, A/cm2 was achieved at 77, K under self-field.

In the production of melt-textured RE-Ba-Cu-O bulk superconductors, the precursors are generally prepared by uniaxial and/or cold-isostatic pressing of raw powders. The employment of fine starting powders is effective in fabricating high-performance RE-Ba-Cu-O bulk superconductors. However, cracks often form in the green bodies when fine powders are unaxially pressed. In this work, we have investigated the defects in green bodies during the powder compression process for bulk superconductor fabrication. Fine and large YBCO powders and granulates of binder-added fine powder were uniaxially pressed into tablets (20 mm in diameter) using different pressures from 31 to 125 MPa. When the fine powder was pressed at pressures above 62 MPa, several defects such as lamination, capping and cracks on the parallel in the direction of pressing were found in green bodies. These defects in green bodies partially remained after melt-processing and affected the field-trapping abilities of melt-textured bulk samples. The addition of an organic binder is very effective method for reducing defects in green bodies.

We have studied the microstructure of melt-growth GdBa2Cu3O7−δ (Gd123) bulk superconductors with the addition of Gd2Ba4CuMOx (abbreviated as M2411 with M = Mo or Zr) particles by transmission electron microscopy. Gd123 bulks are prepared with nominal compositions Gd123+(0.4−x) Gd211+xM2411+0.1 BaO2 in a molar ratio with x = 0–0.2. The addition of M2411 particles induced nanosized particles inside bulks. They are apparently distributed well under seeding positions, where fewer Gd211 particles are located. The observed nanosized particles assigned as M2411 may play the role of flux pinning centres, leading to an enhanced Jc. However, the addition of M2411 with x>0.12 leads to the appearance of excess liquid and macrodefects in the bulks. Enhanced interfacial stress induced by the excess M2411 addition was found, together with modified local chemical compositions. These results account for both the suppression of the superconducting properties and the formation of the band structure in the present system.

The paper provides an experimental basis for preparing large grain (Nd0.33Eu0.27Gd0.39)Ba2Cu3Oy “NEG-123”. MgO seeds proved to be efficient in controlling growth orientation when a small quantity of ZnO of around 0.035 wt.% was added to the NEG-123 matrix. A substantial reduction of liquid phase loss was observed for a proper ZnO concentration. A perfect facet line up to the bottom of the sample with c-axis reflection plane was observed after the melt-growth implying high density of the material and practically no liquid loss. The magnetization measurements suggested that the superconducting transition temperatures were not affected up to 0.035 wt.% ZnO addition. Critical current density Jc, measured at 3 T and 77 K (Ha∥c-axis), increased with increasing ZnO content up to 0.035 wt.%, where it reached maximum value of 100 kA/cm2 and decreased thereafter. The scalling analysis of the pinning force density as a function of the reduced field h = Ha/Hirr (Hirr is the irreversibility field) showed a peak at relatively high position as expected for an optimized pinning structure. The present results indicate high potential of ZnO particles for further enhancement of the material performance.

By using top seeding melt-textured growth process, single domain bulk superconductor GdBa 2 Cu 3 O 7− δ (Gd-123) was prepared in air with variable additions of nanosized SnO 2 and ZrO 2 powders. The inhomogeneous distribution of Gd 2 BaCuO 5 particles was observed by scanning electron microscope study for each bulk with nanoparticles addition. A band structure composed by second phase free band, narrow second phase rich band and second phase diluted band was observed along both a – b plane and c growth sectors in the vicinity of seed site. At 77 K high critical current ( J c ) was increased up to 99,300 A cm −2 under self-field in H ∥ c -axis configuration in Gd-123 bulk with 0.004 ZrO 2 addition, molar ratio to Gd-123. J c has a remarkable spacial distribution inside the samples while keeping T c almost stable for all addition quantities.