Effect of Different Nanosized MgO on the Transport Critical Current Density of Bi1.6Pb0.4Sr2Ca2Cu3O10 Superconductor

Magnesium oxide powders with average particle size 20 and 40 nm were added into Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ (Bi,Pb-2223) with nominal composition Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀(MgO) _x (x=0–0.15 wt.%). The transport critical current density (J _c) and transition temperature were determined using the four-probe method. The structure and microstructure were examined by X-ray diffraction method and scanning electron microscopy, respectively. The transition temperature and J _c increased with nanosized MgO addition. The 20 nm MgO added samples showed a higher J _c compared with the 40 nm MgO added samples. J _c was higher as size of MgO was closer to the coherence length of the superconductor. These results showed that the size variation of flux pinning center at the nanoscale is important in enhancing J _c.     

Enhanced Electrical Transport Properties of Nano NiFe2O4-added (Bi1.6Pb0.4)Sr2Ca2Cu3O10 Superconductor

The effect of nanometer sized NiFe₂O₄ (∼15 nm) addition in Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ (Bi2223) superconductor was studied. The (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀ superconductor was prepared through the co-precipitation method and 0.01 wt% to 0.05 wt% of nano NiFe₂O₄ was added. The critical temperature (T _c), critical current density (J _c), phase formation and microstructure were investigated. All samples showed a major Bi2223 phase with (Bi,Pb)₂Sr₂CaCu₂O₈ (Bi2212) as the minor phase. The sample with 0.01 wt% nano NiFe₂O₄ showed the highest T _c and J _c: of more than 3 orders of magnitude higher than the non-added sample at 77 K. A further nano NiFe₂O₄ addition (>0.01 wt%) leads to degradation of T _c and J _c. These results indicate that addition of an optimum amount of NiFe₂O₄ nanoparticles can effectively enhance the transport critical current density in this system.     

Melt-textured Bi1.6Pb0.4Sr2Ca2Cu3O11 bulk superconductors fabricated in a simple tube furnace

Using the simplified version of the melt-textured growth (MTG) technology with a simple tube furnace, we have fabricated superconductors satisfying the nominal composition Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₁. We would note that the material used in the fabrication was prepared by mixing a precursor Bi_1.6Pb_0.4Sr₂Cu₃O _x and CaO powder. This two step technique was found to be superior to the single step solid state reaction method after many trials. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) morphologies show that the melt-textured bulk samples are made up of stacks of highly textured single crystal-like layers. X-ray analysis as well as d.c. magnetization measurements were carried out and theJ _c value was found to be 1.3×10³ A cm^–2 at 77 K using the Bean model. At this stage, thoughJ _c is not so high as that of the best samples obtained from other complicated methods involving special (hot) pressing and sintering techniques, we do not need to apply any mechanical treatment at or after the heating procedure.     

The Effect of Mn Substitution on Properties of Bi1.6Pb0.4Sr2Ca2?x Mn x Cu3O y Superconductors

The effects of Mn substitution on the physical properties and structural characteristics of Bi_1.6Pb_0.4Sr₂Ca₂Cu_3−x Mn _x Oy (Bi-2223) superconductor system have been studied. For this, the samples of nominal composition Bi_1.6Pb_0.4Sr₂Ca₂Cu_3−x Mn _x Oy (x=0.00, 0.10, 0.15 & 0.20) was prepared by the solid-state reaction method. It has been found that the effects of Mn substitution favor the formation of Bi-2223 phases. The phase identification/gross structural characteristics of synthesized (HTSC) materials explored through powder X-ray diffractometer reveals that all the samples crystallize in orthorhombic structure with lattice parameters (a=5.4918 ?, b=5.4071 ?, and c=37.0608 ?) up to Mn concentration of x=0.20. The critical transition temperature (T _c) measured by standard four probe method has been found to depress from 108 K to 70 K and transport current density (J _c) has been increased from 4.67×10² to 3.52×10³ A cm⁻² as Mn content (x) increases from 0.00 to 0.20. The surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM and AFM) results that voids and grains size increases as the Mn concentration increases besides the nanosphere like structures on the surface of the Mn doped Bi-2223 sample.     

Production of a superconducting Bi-Pb-Sr-Ca-Cu oxide wire using a hot-extrusion process

A Bi_1.84Pb_0.34Sr₂Ca₂Cu₃O_y sample, sheathed with Ag, was hot-extruded into a wire with a high reduction ratio of 91 % in area. The c axis of the extruded oxide was normal to the extrusion direction. Subsequent swaging and rolling at room temperature and annealing for 200 h at 1113 K in air resulted in a high-T_c superconducting composite tape exhibiting a J_c value of 5900 A/cm² at 77 K in zero applied field. The hot-extrusion process is useful as the first deformation process to produce the superconducting oxide tape with a favorable orientation structure.     

The effect of the number of Ag layers on some physical properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox

Bi_1.8Pb_0.4Ca_2.2Sr₂Cu₃O_x/Ag multilayered samples with 2, 4 and 8 layers are prepared by powder in tube (PIT) method and the effect of multilayering with Ag on the superconducting and the microstructural properties of Bi_1.8Pb_0.4Ca_2.2Sr₂Cu₃O_x is studied. The investigations consist of XRD, SEM, EDS, magnetoresistivity, and I–V measurements. In the magnetoresistivity measurements, magnetic fields up to 0.5 T are applied both parallel and perpendicular to the current flow direction. The superconducting and microstructure properties of the samples are enhanced as the number of Ag layers are increased. The samples are composed of a highly oriented Bi-2223 phase in the regions near the Ag layers. The formation of the dense oriented structure is near the interface between oxide and the Ag layer. T_c and J_c values are enhanced from 107 to 109 K and from 240 to 600 A/cm² by increasing the number of Ag layers, respectively. The results suggest that Ag plays an important role in the improvement of superconducting properties. The possible mechanisms of the enhancement of superconducting properties due to Ag layering are discussed.     

Transport critical current density of Bi–Sr–Ca–Cu–O/Ag superconductor tapes with addition of magnetic nanopowder γ-Fe2O3

The effect of sintering temperature on the transport properties of Ag-sheathed-(Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀–(γ-Fe₂O₃)_0.01 superconductor tapes prepared by the powder-in-tube technique with sintering time fixed at 50 h has been investigated. The maximum transport critical current density, J_c of 6490 A/cm² at 77 K, was observed at sintering temperature of 845 °C. A further single intermediate rolling step increases J_c to 9560 A/cm². Sintering temperature from 830 to 845 °C increases the 2223 phase content and resulted in improved J_c. At 850 °C, the content of 2223 phase decreased resulting in a corresponding decrease in J_c. X-ray diffraction patterns suggest that the 2212 phase reacts with non-superconducting phase such as CaCuO₂, (SrCa)₂CuO₃, CaO, and CuO to form the 2223 phase. Samples without γ-Fe₂O₃ prepared under the same condition showed a lower J_c with maximum at 1560 A/cm². Our results show that nanomagnetic γ-Fe₂O₃ addition improved J_c which supports previous calculations on the possibility of frozen flux superconductor with nanomagnetic addition in this class of materials.     

Properties of superconducting, polycrystalline dysprosium-doped Bi1.6Pb0.5Sr2−xDyxCa1.1Cu2.1O8+δ (0 ≤ x ≤ 0.5)

The structural and superconducting properties of dysprosium (Dy) doped (Bi,Pb)-2212 superconductor have been studied. Dy concentration is varied from x = 0.0 to 0.5 in a general stoichiometry of Bi_1.6Pb_0.5Sr_2−xDy_xCa_1.1Cu_2.1O_8+δ. It is found that the Dy atoms enter into the crystal structure by replacing Sr atoms and induce significant change in lattice parameter, microstructure, hole-concentration and normal state conductivity of the system. The critical temperature (T_C) and critical current density (J_C) at self-field of the Dy-doped samples enhance considerably at optimum doping levels. Maximum T_C of 92.3 K (for x = 0.4) and J_C of 1390 A/cm² at 64 K (for x = 0.2) are observed for doped samples as against 79.4 K and 127 A/cm², respectively, for the pure sample. The results are discussed on the basis of the change in hole-concentration due to Dy-doping at Sr-site of (Bi,Pb)-2212 superconductor.     

Significant Improvement in Superconductivity by Substituting Pb at Bi-site in Bi2?xPbxSr2CaCu2O8 with x=0.0 to 0.40

Here we report the synthesis and superconducting properties of bulk Bi_2−x Pb _x Sr₂CaCu₂O₈ (x=0.0 to 0.4) compound. Though the superconducting transition temperature (T _c) decreases marginally, the critical current density under magnetic field J _c(H) increases with Pb content. An optimization is observed for x=0.16 with J _c(H) (7.894×10³ A/cm²) that is nearly doubled in comparison to the pristine compound. It seems that controlled substitution of Pb at Bi-site in bulk Bi-2212 (Bi₂Sr₂CaCu₂O₈) system can enhance the superconducting critical parameters. These results are explained on the basis of possible improved inter- and intra-granular properties with Pb substitution in Bi_2−x Pb _x Sr₂CaCu₂O₈ system.     

Oxygen content determination of Bi2Sr2Ca2Cu4O11+x superconductor by thermogravimetric analysis

Thermogravimetric analysis of the individual, binary, ternary, and bismuth-based superconductor mixtures have been carried out to elucidate the excess oxygen content of the Bi₂Sr₂Ca₂Cu₄O_11+x . Our systematic approach eliminates the need to assume initial phase present, original oxygen content, and degree of reduction as in other TG studies. The excess oxygen content of the bismuth superconductor increases fromx=0.38 tox=0.64 after three heating cycles in oxygen atmosphere. Most of the excess oxygen is associated with the highly oxidized copper (Cu³⁺) in the superconducting phase/phases.     

Microstructure controls and their effects on the properties of Bi2Sr2Ca1Cu2Ox superconductors

This paper reports our recent progresses in the development of Bi₂Sr₂Ca₁Cu₂O _x /Ag tape conductors for the applications of magnetic field generation in liquid helium or around 20 K, using a refrigerator. We have carried out extensive work to optimize the processing parameters, investigating the relationship between the microstructure and transportJ _c. We have found that the partial melting in oxygen atmosphere is effective to have large transportJ _c with good reproducibility. The pre-annealing and intermediate rolling (PAIR) process has been successfully applied to the multilayer conductors to improve the grain alignment and transportJ _c. TheJ _c of 5×10⁵A/cm² at 4·2 K and 10 T has been achieved, which is the highest value reported so far. Two magnets fabricated by using different types of Bi-2212/Ag conductors were tested. One is a magnet designed as an insert magnet for a 18 T-class large bore Nb-Ti/Nb₃Sn superconducting magnet. The conductor of this magnet was multifilamentary tape processed by powder-in-tube method. TheI _c was 98 A in the backup field of 18 T, which generated the self field of 1·79 T. A large pancake coil was fabricated with multilayer conductor and tested under the operation of cryocooler system. The coil was stably operated up to theJ _c of the coil at the temperatures below 30 K.     

Fabrication of Bi2Sr2CaCu2O x /Ag superconducting tape using a screen-printing method

High- T _c superconducting Bi₂Sr₂CaCu₂O _x /Ag tape was successfully fabricated using a screen-printing method and a partial-melting process. A highly oriented layer structure was achieved and confirmed by X-ray diffraction (XRD), pole-figure measurement and scanning electron microscopy (SEM). The critical current density, J _c, of the tape at 77 K, 0 T, was about 20000 A cm^–2. High-temperature XRD was used to clarify the mechanism of the grain alignment. An aligned structure of the 2212 phase was originated from Bi-free compounds, such as (Sr,Ca)CuO₂ and (Sr,Ca)₂CuO₃ developed during a holding stage at 875°C.     

Zero resistance at 117 K in Bi1.6Pb0.4Sr2Ca2Cu2+xOy compounds

In the Pb-doped Bi-Sr-Ca-Cu-O system, optimization of the composition and heat treatment conditions at which a greater amount of the high-T _c phase forms has been reported in our early paper [1], where the temperature of zero resistance was 107K. Recently, we have achieved zero resistance at 117 K and observed an a.c. susceptibility step at around 150 K by changing the Cu composition in the Bi^1.6Pb^0.4Sr²Ca²Cu^2+x O ^y system (x=0, 0.4, 0.8, 1.2, and 1.6).     

The Comparisons Between Y-123 and Y-124 Superconductor Substituted with Ca at the Cu-Site

The comparison between YBa₂Cu_3?x Ca _x O _δ and YBa₂Cu_4?x Ca _x O₈ superconductors substituted with Ca at the Cu-site was investigated. The concentration of Ca varied from x=0.00 to x=0.15. Resistivity and current density measurement (without magnetic field) were measured using four-probe method. The samples were characterized using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). From the resistivity measurement, the critical temperature (T _c?zero) in x=0.00 was 84 K for Y-123 and 83 K for Y-124 superconductor system. As the Ca concentration increased to x=0.15, both superconductor systems showed a decrease in value whereby 71 K for Y-123 and 74 K for Y-124. This was a result of the decrease in the hole concentration. Critical current density (J _c ) decreased with the further increment of Ca concentration owing to grain connectivity and an increase of porosity. At 50 K, J _c decreased from 3.9790 A/cm² at x=0.00 to 3.5184 A/cm² at x=0.15 for Y-123, and from 3.6209 A/cm² at x=0.00 to 0.5243 A/cm² at x=0.15 for Y-124. The crystallographic crystal structure showed that both Y-123 and Y-124 superconductor systems exhibited an orthorhombic form. FESEM microscopy showed that the Y-123 sample had less porosity compared to Y-124 samples and the resulting Y-123 sample had a higher J _c compared to the Y-124 sample.     

Superconductivity in epitaxial Bi2Sr2CuO6/Bi2Sr2CaCu2O8 superlattices: The superconducting behavior of ultrathin cuprate slabs

Utilizing atomic layer-by-layer molecular beam epitaxy (ALL-MBE), we have synthesized a series of high-quality superlattices in which ultrathin slabs (one-half unit cell thick) of the high-T _c superconductor Bi₂Sr₂CaCu₂O₈ alternate with up to five such layers of the low-T _c Bi₂Sr₂Cu₁O₆ phase. In all these superlattices we foundT _c to be essentially equal to that of the high-T _c Bi₂Sr₂CaCu₂O₈ phase itself, which indicates that this cuprate is a 2D superconductor insofar as the interslab coupling plays at best a secondary role. Furthermore, it is demonstrated thatT _c need not be reduced at heterostructure interfaces.     

Improvement of the critical current density in Bi-2223 ceramics by sodium–silver co-doping

Bi_1.46Pb_0.36Ag_0.18Sr₂Ca₃Cu_4?xNa_xO_y (x = 0, 0.05, 0.1 and 0.25) samples were prepared by a conventional solid state reaction method. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, dc electrical resistivity and magnetic-hysteresis loop measurements. It has been shown that the Na doping in low contents significantly improves the physical properties of Bi-2223 phase. Magnetic hysteresis measurements have shown that the largest hysteresis curve belongs to Bi_1.46Pb_0.36Ag_0.18Sr₂Ca₃Cu_3.95Na_0.05O_y sample including x = 0.05 Na content, indicating that it has best flux pinning capability in samples produced in this work. In addition, J_c values of the samples were calculated from the hysteresis loop measurement by using the Bean’s model showing that J_c increases with small amounts of sodium–silver co-doping.     

Effects of TiO2 addition on the superconducting properties of Bi-Sr-Ca-Cu-O system

The effects of TiO₂ addition in Bi₂Sr₂CaCu₂O₈Ti_y (Bi-2212) with y = 0, 0.05, 0.10 and 0.15 and (Bi_1.6Pb_0.4)Sr_1.6Ca₂Cu_2.8O₁₀Ti_y (Bi-2223) with y = 0, 0.10,0.20 and 0.40 are studied and compared. The samples have been investigated by powder X-ray diffraction (XRD), dc electrical resistance, critical current density (J_c) and scanning electron microscopy (SEM). The XRD patterns of the Bi₂Sr₂CaCu₂O₈Ti_y materials showed the Bi-2212 as the dominant phase. In the TiO₂ added samples (with x = 0.05 and 0.1), the c lattice parameter decreased slightly from the non-added sample showing the possibility of Ti incorporating into the crystal structure of the Bi-2212 phase. In the undoped (Bi_1.6Pb_0.4)Sr_1.6Ca₂Cu_2.8O₁₀ material, the XRD pattern showed the existence of mixed phases of Bi-2223 and Bi-2212. The TiO₂ added Bi-2223 samples do not show any systematic variation in the c lattice parameter, indicating that Ti may not be incorporated into the Bi-2223 crystal structure. The T_c values in both systems decreased with the addition of TiO₂. The critical current densities, J_c at 40 K in the Bi₂Sr₂CaCu₂O₈ system and at 77 K in the (Bi_1.6Pb_0.4)Sr_1.6Ca₂Cu_2.8O₁₀ system also decreased with the addition of TiO₂. SEM micrographs of both systems showed a slight decrease in average grain size when TiO₂ was added.     

The Effect of Eu Substitution onto Ca Site in Bi(Pb)-2223 Superconductor Via Co-precipitation Method

The samples with nominal composition of Bi₁₆Pb_0.4Sr₂Ca_2?x Eu _x Cu₃O _y where x=0.000, 0.025, 0.050, 0.100, and 0.200 prepared by co-precipitation method (COP) have been investigated. They were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), electrical and resistivity measurement using the four-probe method. The temperature dependency on electrical resistance showed the superconducting behavior for all the samples. The critical current density (J _c ) and superconductivity transition temperature (T _c?zero) of Eu substituted were found to be lower than those of the pure sample. T _c?zero varied between 100 and 73 K towards Eu concentration with the highest T _c?zero in the Eu substitution was found at 98 K for x=0.025 and decreased gradually for further substitution of Eu corresponding to a small change in the carrier concentration. J _c decreased with increasing Eu substitution, and it was measured to be at 5.7512 A/cm² in the Eu free sample and at 2.1223 A/cm² for the x=0.025 sample at 77 K. XRD analyses showed the decrease of the volume fraction of Bi-2223/Bi-2212 (%) which were estimated from 78.13/21.87 for x=0.000 to 23.18/76.82 for x=0.200. The crystallographic structure was found to change slightly from tetragonal to orthorhombic in Eu substituted samples. The lattice parameter c of the Eu samples decreased due to the incorporation of Eu³⁺ (0.95 Å) with smaller ionic size at the Ca²⁺ (0.99 Å) site. From the SEM investigation, the grain connectivity became weak and the porosity increased with the increment of Eu concentration, resulting in the decrease of J _c .     

Effect of Eu2O3 Nanoparticles Addition on Structural and Superconducting Properties of BSCCO

To study the effects of Eu₂O₃ nanoparticles addition to BSCCO superconducting system, four bulk polycrystalline samples with general formula of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O _y +xEu₂O₃ (where x=0.0, 0.3, 0.5, 1.0 wt%) were prepared by chemical sol–gel method. X-ray diffraction, SEM, and TEM were used for structural characterization of the samples. DC electrical resistivity, critical current, and AC magnetic susceptibility were measured. XRD analysis showed that both (Bi,Pb)-2223 and Bi-2212 phases coexist in the samples having orthorhombic crystal structure. DC electrical resistivity, J _c , and AC magnetic susceptibility measurements reveal that adding Eu nanoparticles to BSCCO improves superconducting properties of this system and enhances its critical current density. The enhancement of the J _c may be caused by improvement of the grain connectivity with Eu nanoparticle additions.     

Effects of Ni Substitution in Bi-2212 Superconductors

In this study the samples were synthesized from a 2234 stoichiometric composition in order to obtain a large amount of pure 2212-BSCCO. The effects of Ni substitution on the properties of Bi-based Bi_2?x Ni _x Sr₂Ca₁Cu₂O _y superconductor with x=0, 0.05, 0.1 and 0.2 were investigated by means of X-ray analysis (XRD), DC electrical resistivity and magnetic-hysteresis loop measurements. It has been found that the T _c (onset) transition temperature does not change independently of Ni content. In addition, J _c values of the samples were calculated from the hysteresis loop measurement by using Bean??s model, showing that J _c decreases with increasing Ni substitution.