GdBCO Bulk Superconductors Research Articles

The levitation force and stiffness enhancement of single domain GdBCO bulk superconductor by an axial background magnetic field

How to improve the levitation force (FL) and its stiffness between a permanent magnet and a REBCO bulk superconductor is one of the most key and attractive problems to be solved for practical applications. In this paper, we provided a novel hybrid magnet added superconductor system (HMS) to enhance the levitation force and the stiffness, the HMS sample is assembled by a single domain GdBCO bulk with an attached permanent magnet (PM) serving as an axial background magnetic field. The results indicate that (1) the FL increased first and decreased then with the increase of the PM diameter (dPM), the largest FL is achieved when the dPM approaches the diameter of the GdBCO bulk, FL has been improved up to 152% with a thinner PM; (2) the FL increased with the increase of the PM thickness and saturated at a certain value, FL have been improved up to 168% with a thicker PM; (3) the stiffness of FL has been improved up to 187% and 201% with the increase of the PM diameter and thickness; (4) the FL and its stiffness enhancement dependent on the positive trapped field of the field cooled HMS samples. The results are of great significance to improve the performance and stability of maglev systems, the mechanism for enhancing the levitation force and stiffness property has been investigated in details.

Enhanced performance of GdBCO bulk superconductors by doping a new kind of YGdBa4CuNbO y nanoparticles

In this work, a new kind of YGdBa4CuNbO y (YGdNb-11411) nano-particles was designed and sintered using a solid-state reaction method, whereas their impact on the performance of GdBCO bulks was investigated for the first time. From the acquired x-ray diffraction data and scanning electron microscopy imaging results, it was proved that the YGdNb-11411 particles were of excellent chemical stability and did not react with other phases during the crystal growth process. The YGdNb-11411 particles ranged from 80 to 130 nm and they were uniformly distributed in the well-textured GdBCO bulk superconductors. The maximum critical current density (J c-max) of the samples was enhanced from 3.48 × 104 A cm−2 to 8.63 × 104 A cm−2 (77 K) in the self-field as the doping amount increased from 0 wt% to 7 wt%. In addition, the GdBCO sample with YGdNb-11411 particles also showed an enhanced flux pinning force density and relatively high J c around the magnetic flux density range of 1 T–2 T (77 K). These results clearly indicated that the YGdNb-11411 particles could effectively enhance the properties of the GdBCO bulk superconductors.

A novel method for fabricating of high-performance multi-seeding GdBCO bulk superconductors

A novel multi-seeding (NMS) method is proposed for improving the performances of GdBCO samples by optimizing the shapes and the space configurations of the single-domain GdBCO grains. Three multi-seeding GdBCO bulk superconductors with dimensions of 60 × 20 × 14 mm3 were fabricated by a Gd + 011 infiltration growth method with different seeding techniques: samples S1 and S2 by the traditional multi-seeding method (TMS) with two and three seeds, respectively; and sample S3 by the NMS method with three seeds. The results show that among the three, sample S3 has both of the largest levitation force, 111 N, and the largest magnetic field coupling ratio, 68.57%, which are clearly higher than the levitation force of 100 N and 90 N, and the magnetic field coupling ratios of 34.25% and 11.33% for the samples S1 and S2, respectively. These results indicate that the NSM method is a useful way to improve the mechanical strength, homogeneity, and performances of multi-seeding GdBCO samples.

Effect of stacking height on the levitation force and trapped field properties of GdBCO bulk superconductor

Effect of stacking height on the levitation force and trapped field properties of GdBCO bulk superconductor

A low-cost approach for recycling large GdBCO bulk superconductors using an infiltration technique with different liquid sources

The high-temperature superconductor has become a research hotspot, because of its high critical temperature, strong trapped flux density, stable suspension characteristics and large magnet levitation force. Single-domain REBa2Cu3O7−δ (REBCO) superconductors, where RE is a rare-earth element such as Y, Gd, Sm or Nd, have wide and potential applications in high-tech fields, such as micro-magnet superconducting maglev trains, superconducting motors and superconducting magnetic separation systems. However, a large number of multi-domain samples are easily produced in the preparation process, resulting in a significantly lower success rate and a significant increase in cost, which restricts their practical applications. Thus, we successfully recycle a series of GdBCO samples by re-supplementing the liquid phase lost in the primary growth process and pre-treating the failed sample as solid-phase source billets, which was proposed by Shi. The growth morphology and superconducting properties of the recycled GdBCO bulk superconductors are investigated in detail in this study. The results show that the key superconductivity properties have been significantly improved, which provides the scientific basis and new ideas for the development of low-cost and highly efficient fabrication yields of REBCO bulk superconductors.

Fabrication process and superconducting properties of recycling multi-domain GdBCO bulk superconductors using improved infiltration technique

High temperature superconductor has become one of the hotspots of research, because of its high critical temperature, strong trapped flux density, stable suspension characteristics and large magnet levitation force. The single domain REBa<sub>2</sub>Cu<sub>3</sub>O<sub>7–<i>δ</i></sub> (REBCO) superconductors have the wide and potential applications in the high-tech fields, such as micro-magnet superconducting maglev train, superconducting motor and superconducting magnetic separation system. However, a large number of multi-domain samples are easy to produce in the preparation process, which leads the success rate to decrease significantly and the cost to increase considerably, which restricts its practical application process. Inspired by the top seeded infiltration growth method, we develop a reliable method of recycling failed GdBCO sample by re-supplementing the liquid phase lost in the primary growth process and pretreating the failed sample as solid phase source billets. We recycle a series of GdBCO samples by using this new technique successfully. The growth morphology, superconducting properties, and microstructures of the recycled GdBCO bulk superconductors are investigated in detail in this study. The results show that the magnetic levitation forces of the recycled GdBCO samples are all greater than 30 N, their magnetic flux densities are all above 0.3 T, and their capture efficiencies are above 60%. These results provide the scientific basis and new ideas for developing the low cost and high efficient yield of fabrication of the REBCO bulk superconductors.

A Practical Processing Method for the Fabrication of NdBCO Seed Crystals and High-Performance Single-Domain GdBCO Bulk Superconductors

NdBCO seed crystals and high-performance GdBCO bulk superconductors were prepared successfully by a modified top-seeded melt-textured growth (TSMG) process and by Gd + 011 top-seeded infiltration growth (TSIG) process. The modified TSMG process used a new composition powder (NCP, 0.9 Nd2O3 + 2.4 BaCuO2 + CuO) instead of the conventional composition powder (CCP, NdBa2Cu3O7-x + 0.4 Nd2BaCuO5), the GdBCO bulk superconductor seeded by the self-made NdBCO seed crystal. In the whole procedure above, only one precursor powder (BaCuO2) needs to be sintered, three kinds of powder and three pellets are required, so time and energy consumption were greatly reduced. The results of thermal analysis and X-ray diffraction (XRD) patterns revealed the reaction mechanism of the modified TSMG process. Superconductivity properties of the GdBCO sample were measured employing a levitation force measurement system and a vibrating-sample magnetometer (VSM); the maximum value of the levitation force of the GdBCO sample was 44.78 N (77 k, 0.5 T); the onset superconductivity transition temperature (Tc) was approximately 93.7 K; the transition width was 6.2 K, and the maximum value of critical current density (Jc) was 1.5 × 105 A∙cm−2 (0 T, 77 K). These results indicate that, by combing the modified TSMG process and Gd + 011 TSIG process, a practical processing method for preparing the NdBCO seed crystals and the high-performance single-domain GdBCO bulk superconductors was developed.

The effect of the magnetic field distribution of permanent magnets on the trapped field properties of a single domain GdBCO bulk superconductor

The trapped field properties of a single domain GdBCO bulk superconductor with a diameter of 32 mm after being magnetized with different permanent magnets under a field cooling state at 77 K have been investigated. The results show that the maximum trapped field of the sample (Bmtr) is nearly saturated when the diameter of the permanent magnet d ≥ 20 mm, but the trapped magnetic flux of the sample (Φs) is nearly saturated when d ≥ 30 mm. This indicates that the largest trapped magnetic flux can be obtained when the size of the permanent magnet is close to that of the sample, and it is not necessary to use a more permanent magnet. In addition, a new and unusual phenomenon is found in that Φs is greater than the magnetic flux of the permanent magnet (ΦPM) when the diameter ratio between the permanent magnet and the sample is less than a certain value, such as 0.63 in this experiment. The relationship between Φs and ΦPM was well expressed as These results can provide a new method to design and control the trapped field properties of a single domain REBCO bulk superconductor during practical applications.

How to Control the Gd211 Particles and Enhance the Levitation Force of Single Domain GdBCO Bulks Prepared by the Gd+011 TSIG Method

In order to control and refine Gd211 particle size in GdBCO bulks, two group of single domain GdBCO bulk superconductors have been prepared with different solid phase pellets sintered at different temperature (T) and times by the Gd+011 TSIG method. The results of the first group of single domain GdBCO bulks indicate that: the average size of Gd211 particles in precursor solid phase pellets increase with T increasing up to 1200 °C; the density of the precursor solid phase pellets increases with the increasing of T when T is larger than 950 °C, but lower than that of the as-pressed pellets when T less than 1000 °C; the average size of Gd211 particles in the single domain GdBCO bulks decreases first and increases then with the increasing T; the maximum levitation force is obtained in the sample with a relatively larger size of Gd211 particles and higher density. The second group of samples has also been prepared with the solid phase pellets sintered at 1000 °C but with different times, the results indicate that: the largest levitation force is about 38% higher than that of the best samples mentioned above. The results are discussed in detail.

Numerical simulation of dynamic fracture behavior in bulk superconductors with an electromagnetic-thermal model

Single-grain GdBCO bulk superconductors have significant applications potential due to their ability to trap stable and large magnetic fields. The internal fracture of these bulk superconductors caused by Lorentz force and thermal load is a key issue in their practical applications. The aim of this work presented here is to investigate the mechanical behavior of the bulk superconductor during pulsed field magnetization. The H-formulation and heat transfer equation are used to obtain the electromagnetic force and thermal load in the bulk with and without defects. Numerical simulations show strong local enhancement of the electromagnetic load at the crack tips. Moreover, dynamic stress intensity factors at the crack tips are presented based on the two-dimensional state-based peridynamic theory. In addition, the crack propagation path is predicted. Finally, different dynamic crack problems are considered to discuss the influence of crack, void, inclusion, and hole on the mechanical stability of the bulk. Results show that defects increase the risk of damage of superconducting bulks.

XFEM analysis of the fracture behavior of bulk superconductor in high magnetic field

A bulk superconductor in a high magnetic field is subjected to a large electromagnetic force, which can cause crack propagation and damage the bulk. In this paper, we study the fracture behavior of the GdBCO bulk superconductor under a large electromagnetic force based on the Extended Finite Element Method (XFEM). The critical state Kim model and H-formulations are used to obtain the electromagnetic force of a bulk superconductor in the magnetic field first. Second, the Stress Intensity Factor (SIF) of the bulk superconductor for various cracks under the electromagnetic force is presented. Numerical results show that the SIF depends not only on crack angle and length but also on the width of the bulk. For the inclined crack with a large crack angle, with the crack length increase, the SIFs increase first and decrease, while for a small crack angle, the SIFs decrease with the crack length increase. For the kinked crack, the SIFs decrease with the crack length increase. With the XFEM, the growth of the inclined and kinked cracks in the bulk superconductor during field cooling is presented. The crack propagation paths are dependent on the size of the bulk and different for two crack problems. In the process of crack propagation, the propagation path has a certain degree of deflection angle compared with the initial crack.

The Effect of Cone Additional Permanent Magnet Thickness on Magnetic Field Distribution and the Levitation Force of Single Domain GdBCO Bulk Superconductor

It has been investigated that the interaction force between truncated cone permanent magnet (PM) and a GdBCO bulk (HTSC) superconducting permanent magnet (SCPM) magnetized by a truncated cone permanent magnet in their configurations at 77K. The influence of two configurations in different thickness of truncated cone permanent magnets of single domain GdBCO bulk capture field and superconducting magnetic levitation force results. The maximum superconducting magnetic levitation force first increases as H increase, and then decreases with H when it reaches a certain value, from 5.7N to 16.6N at first, and then it decreases to 3.8N. The vertical component of the magnetic field intensity on the top surface (h=2mm) of truncated cone permanent magnet first increases, and then decreases also, from 0.20T to 0.54T, and then decrease to 0.25T. These results indicate that the levitation force of high temperature superconductor bulk can be effectively improved by scientific choosing of shape and size of permanent magnet, and reasonable designing of the system configurations, which is very important during the practical design and applications of superconducting magnetic levitation system.

A Low-Cost Fabrication Technique for the Growth of Single-Domain GdBCO Bulk Superconductor from Raw Metal Oxides

A single-domain GdBCO bulk superconductor is usually fabricated using a mixture of pre-reacted precursor powders (including GdBa2Cu3O7−δ and Gd2BaCuO5) by the top-seeded melt texture growth (TSMTG) process. However, the synthesis of pure-phase precursor powder by the solid-state sintering reaction can not only consume time for weeks but also prolong the fabrication process and can lead to a low-efficiency and high-cost process. In this paper, we reported the successful growth of single-domain GdBCO bulk superconductors by the top-seeded metallic oxide melt growth (TS-MOMG) process in which the raw materials of Gd2O3, BaO, and CuO, the three different metallic oxides, are just involved to fabricate the single-domain GdBCO bulk superconductors. After detailed investigations in the morphology, levitation force, trapped magnetic field, and critical temperature of the grown samples with different ratios, it was found that the simplified precursor-phase source can be used to fabricate the single-domain GdBCO bulk superconductors more efficiently, which can combine the crystal growth procedure and greatly economize the preparation cost and the time to the most extent.

Effects of Gd211 Particles Characteristic in the Precursor Pellets on the Levitation Force of Single‐Domain GdBCO Bulks Prepared by the Gd + 011 TSIG Method

In this paper, single‐domain GdBCO bulks have been fabricated by a new Gd + 011 TSIG method with precursor solid phase pellets (PSPPs) of different Gd211 particle sizes and distributions, prepared by solid state reaction with well‐mixed (Gd2O3 + BaCuO2) pellets at different temperatures. The novel results indicated that (1) the average size of Gd211 particles in PSPP is monotonically increasing with increasing the sintering temperature up to 1200°C. (2) With increasing the sintering temperature from 950 to 1200°C, the porous ratio and the density of the PSPP are, respectively, monotonically decreasing and increasing. Furthermore when the sintering temperature is less than 1000°C, the porous ratio is higher and the density is lower than the values of the pressed pellets. (3) With increasing the sintering temperature, the average size of Gd211 particles in the GdBCO bulk first decreases and then increases. In addition, the smallest Gd211 particles are obtained in the sample sintered at 1050°C. (4) The maximum levitation force is obtained in the sample sintered at 1150°C with a relatively larger size of Gd211 particles and lower porosity. This result is significant when fabricating high‐quality GdBCO bulk superconductors by controlling the porosity, Gd211 particle size, and their distribution characteristic.

Effect of inner diameter of hollow cylindrical permanent magnet on levitation force of single domain GdBCO bulk superconductor

The influence of inner diameter of hollow cylindrical permanent magnet on the levitation force of single domain GdBCO bulk superconductor is investigated by measuring the levitation force between the hollow cylindrical permanent magnet and the single domain GdBCO bulk superconductor. The results show that the levitation force is closely related to the inner diameter of the hollow cylindrical permanent magnet when the inner diameter (d) increases from 0 mm to 26 mm (minimum measuring gap distance Z=2 mm), and all the superconducting magnetic levitation force curve shows magnetic hysteresis phenomenon. With the increase of the inner diameter of the hollow cylindrical permanent magnet, the levitation force at a minimum distance decreases gradually from 14.8 N at d=0 mm to -0.1 N at d=26 mm. The levitation force at the minimum gap distance is negative when d ≥ 20 mm. When 0 mm ≤ dd ≥ 5 mm. The larger magnetic field strength of the superconductor can be obtained, and the levitation force can be effectively improved by the scientific and reasonable designing of the permanent magnet structure. The results have certain guiding significance for designing and optimizing the magnetic suspension bearing system, ring track and superconductor.

Significant flux trapping in single grain GdBCO bulk superconductor under off-axis field cooled magnetization

A single grain bulk high-temperature superconductor (HTS) exhibits intensified flux trapping performance upon field cooled magnetization. The world record of trapped flux is 17.6 T achieved by using stacked two-fold GdBCO bulks. However, the majority of magnetization studies focused on the magnetization along the crystallographic c-axis. In the present study, we clarify the flux trapping performance under field cooled magnetization using an off-axis magnetic field with respect to the c-axis. The results show that the trapped flux is almost polarized along the applied field as expected. This tendency remains up to a high off-axis angle θ around 60°. It is worth mentioning that, with θ of 30°, the maximum trapped flux component B//max parallel to the c-axis significantly remains more than 96% of 1.6 T which occurs under on-axis magnetization. Meanwhile, the angular dependence of the c-axis parallel component exhibits that observed flux density is higher than that expected from 1.6 cosθ. In addition, to visualize the flux line upon magnetization at θ of 90°, we successfully demonstrate the continuous flux line trace using steel wires; different trapped flux behaviour appears when applied field penetrates the bulk through the growth sectors centre and along the growth sector boundary, respectively. We interpret these results may come from the microstructure as a result of melt growth. It is highly emphasized that the off-axis magnetization with the finite inclination angle is quite useful for introducing into the design of HTS applications.

Influences of BaO doping on the properties of single domain GdBCO bulk superconductors (II)

In order to inhibit the Gd/Ba substitution in the growth process effectively, a series of single domain GdBCO bulk superconductors with different ratios of BaO additions in the solid phase pellet is successfully fabricated by the modified top seeded infiltration growth technique on the basis of previous research. In the present work, the macroscopic feature, microstructure and critical current density (Jc) of the single domain GdBCO bulk superconductor are investigated in detail. From the top view of the surface of the single domain GdBCO bulk superconductor, all of the samples exhibit clearly the fourfold growth sector boundaries on their top surfaces, and spontaneous satellite grains are observed in none of these samples. It can be seen that the different ratio of BaO addition (from 1 wt% to 4 wt%) cannot affect the growth morphology of the single domain GdBCO bulk superconductor. At the same time, for observations of the microstructure, the small test specimens of dimensions about 2 mm2 mm2 mm are cut from the top surface of the singe domain GdBCO bulk superconductors with different BaO doping ratios and at a distance 5 mm away from the seed, then microstructure analysis is performed in the cleavage phane of the test specimen by using scanning electron microscope. For the sample with 1 wt% BaO doping, the derivative phase of GdBCO (Gd123ss) is found in the Gd123 superconducting matrix. To detect the atomic ratio of the Gd123ss, energy dispersive X-ray spectrometry measurement is carried out on the samples. It is shown that the atomic ratio of the Gd123ss phase is Gd:Ba:Cu=1.566:1.459:3, which proves successfully that the Gd123ss is a kind of phase with lack of barium. With the increase of BaO doping, the phenomenon of lack of barium is effectively controlled and, the nano Gd123ss phase is generated as the flux pinning centre which can be used to improve the superconducting properties in the growth process of GdBCO bulk superconductor. This results can be concluded that the proper doping ratio can control the element substitution effectively, and the solid solution phase can be greatly reduced to some extent, and the critical current can be improved to a certain extent when the amount of BaO added ranges from 2 wt% to 4 wt%, which is very helpful in inhibiting the Gd/Ba substitution and fabricating the high-quality single domain GdBCO bulk superconductors.

Effect of Li doping on the superconducting properties of single domain GdBCO bulks fabricated by the top-seeded infiltration and growth process

Single domain GdBCO bulk superconductors have been fabricated by the top-seeded infiltration and growth process (Gd+011 TSIG) with solid phase compositions of (1-x)(Gd2O3+1.2BaCuO2)+xLi2CO3, (x=0, 0.04, 0.08, 0.10, 0.12, 0.16wt%). The effect of Li2CO3 doping on the growth morphology, microstructure, levitation force, trapped field and critical temperature (Tc) of single domain GdBCO bulks have also been investigated based on these samples. The results show that the single-domain GdBCO bulks can be fabricated when x is in the range of 0–0.16wt%. The size and distribution of Gd211 particles are not influenced by the Li2CO3 doping in the samples. The Tc of the samples decrease from 92.5K (x=0wt%) to 89.5K (x=0.16wt%) when x increases. The decreasing trend of Tc was caused by the substitution of Li+ on Cu2+ site in the GdBCO crystal. Both of the levitation forces and trapped fields of the samples increase first and then decrease with the increase of x; both of the largest levitation force of 38.5N（77K，0.5T） and the largest trapped field of 0.31T（77K，0.5T） are obtained in the sample when x=0.10wt%. These results show that appropriate Li doping is an effective way to enhance the flux pinning force and the other physical properties of GdBCO bulk superconductors fabricated by the Gd+011 TSIG method.

Influences of BaO doping on the properties of singe domain GdBCO bulk superconductors

In this work, a series of single domain GdBCO bulk superconductors with different ratios of BaO addition in the solid phase pellet, is successfully fabricated to inhibit the Gd/Ba substitution in the growth process by the modified top seeded infiltration growth (M-TSIG) technique. The reaction of the precursor powders, the growth morphology, the magnetic levitation force (F), the trapped magnetic flux (Btr) and critical temperature (Tc) of the single domain GdBCO bulk superconductors are investigated in detail. First, the differential thermal analysis is performed on the precursor powders of 10 mg solid phase pellet (containing various amounts of BaO) and 15 mg liquid phase pellet in order to investigate the melting temperature (Tm) and the peritectic temperature (Tp) of the GdBCO superconductor system. The results show that the melting point of the precursor powder decreases by nearly 8℃ as the BaO composition increases from 0 wt% to 4 wt%, which leads to Tp decreasing with BaO content increasing. Second, the top view morphologies of the GdBCO samples are also discussed. All of the samples exhibit clear, fourfold growth sector boundaries on their top surfaces, and spontaneous satellite grains are observed in none of these samples. It can be seen that the different ratio of BaO addition cannot affect the growth morphology of the single domain GdBCO bulk superconductor. And thirdly, the levitation force and trapped field of each of the samples are measured under a zero field cooling state at 77 K by the three-dimensional magnetic force and field device. The values of the levitation force for the samples are slightly different for different ratios of BaO additions. The largest levitation force is 35 N, which is obtained in the sample with 2.5 wt%, and the smallest one is 28 N in the sample with 1 wt% BaO addition. And also, the trapped field of the sample can be attributed simply to the variation in the pinning strength. It can be obviously seen that these values fluctuate between 0.28 T and 0.32 T for these samples. Finally, the critical temperatures of the samples are measured by the vibrating sample magnetometer with an external magnetic field of 0.01 T. The samples exhibit outstanding features of high Tc, which indicates that these samples are of good quality and the Gd/Ba substitution is inhibited by the BaO addition. The above results show that the values of melting temperature (Tm) and peritectic temperature (Tp) of the samples have the decrease tendencies, and the superconducting properties of the samples (such as F, Btr and Tc) can be improved to a certain extent when the amount of BaO added ranges from 2 wt% to 4 wt%, which are very helpful in inhibiting the Gd/Ba substitution and fabricating the high-quality single domain GdBCO bulk superconductors.

Improvement of the Trapped Field Performance of a Holed Superconducting Bulk Magnet

Our goal is to generate a strong magnetic field using a REBCO bulk superconductor activated by pulsed field magnetization (PFM) for industrial application using the bulk magnet. As the diameter of the material increases and its critical current density rises, magnetic field trapping by PFM is difficult due to the strong magnetic shield. We have proposed a holed superconducting bulk magnet to improve the trapped field performance in large-size and high- J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> bulk material. Magnetic flux can be supplied efficiently by reducing superconductivity in the portion with holes artificially. To confirm the validity of the proposed method, an experiment, in which a single pulsed field was applied with changing amplitude of the magnetic field and temperature, was carried out using a GdBCO bulk superconductor with four small holes. Although the magnetic flux penetrated at a lower applied field, there was a problem in that the maximum trapped field and the total magnetic flux decreased. In this paper, the size and number of holes were optimized to manage both the increase in the trapped field and easy flux penetration. A hole 1mm in diameter was drilled to half of depth of the thickness at the rim of a sample after investigating the magnetization characteristic of a GdBCO bulk 60 mm in diameter and 20 mm thick. A trapped field performance was evaluated in the sample, and afterwards, the hole was bored completely to the full depth. Then, the same experiment was carried out. The trapped field for a single hole was improved compared to the four holes, and it was confirmed that the 1-mm-diameter hole did not degrade the magnetization performance.