Improvement of High T c Phase Formation in BPSCCO Superconductor by Adding Vanadium and Substituting Titanium

We have produced the (BiPb)₂V _x Sr₂Ca₃Cu_4?y Ti _y O_12+?? with x=0.1 and y=0.050,0.10,0.2 and 0.3 compounds by melt-quenching method. Structural and superconducting properties of the produced samples were investigated by Scanning Electron Microscopy, X-ray diffraction patterns, electrical resistance measurements and dc-magnetic hysteresis loop measurements. The pure high-T _c phase (2223) is nearly found with Ti substitution for x=0.05 and 0.10. The onset critical temperature (T _c._onset) of the samples increases up to 111 K with doping up to x=0.20. In addition, considerable large values of the critical current densities (J _c), calculated from the hysteresis loop measurements by using Bean??s critical state model are obtained for the samples in the same doping range. Our data have indicated that J _c decreases with increasing temperature and Ti concentration.     

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 Vanadium-Titanium Co-doping on the BPSCCO Superconductor

We have produced the (BiPb)₂V _x Sr₂Ca₃Cu_4?y Ti _y O_12+?? compounds for x=0.05 and y=0, 0.05, 0.10 and 0.20 by glass-ceramic method. The effects of vanadium adding and Ti doping on the structure have been investigated by electrical resistance, scanning electron micrographs (SEM), XRD patterns and magnetic hysteresis loop measurements. It has been found that the high-T _c superconducting phase, (2223), is formed in the samples annealed at 845?°C for 185, with concentration x=y=0.05. However, with increasing Ti doping the (2223) phase transforms into the (2212) phase. We have observed no superconducting properties for x=0.05 and y=0.20 compound. It has completely transformed to semiconductor. In addition, the critical current densities (J _c), calculated from the hysteresis loop measurements by using Bean??s critical state model are obtained for the samples in the same doping range. Our data have indicated that J _c decreases with increasing temperature and Ti concentration.     

Structural, Electrical, and Magnetic Properties of the Co-Substituted Bi-2212 System Textured by Laser Floating Zone Technique

In this work, Bi₂Sr₂CaCu_2?x Co _x O _y (x=0.0, 0.05, 0.10, and 0.25) textured superconductors were prepared by a LFZ melting technique. In all cases, the powder X-ray diffraction patterns of samples show that the Bi-2212 phase is the major one. All samples have good oriented structure, which is a typical picture for superconductors prepared by the LFZ method. Magnetization hysteresis loops, made for all samples at two different temperatures, showed that the loops become narrower with increasing temperature and doping levels. In addition, the effect of Co doping on the critical current density, J _c, of Bi₂Sr₂CaCu_2?x Co _x O _y has been estimated from hysteresis loop measurement by using Bean’s model. The increase of the Co amount in the Bi₂Sr₂CaCu_2?x Co _x O _y structure significantly decreases the critical current density, showing worse connectivity of the grains. All the results indicate that Co substitution for Cu produces the deterioration on the superconducting properties, compared with the undoped samples.     

Enhancement in superconducting transition temperature and Jc values in Na-doped Bi2Sr2Ca1Cu2−xNaxOy superconductors

The effects of Na substitution on the properties of Bi₂Sr₂Ca₁Cu_2?xNa_xO_y were investigated. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, DC electrical resistivity and magnetic-hysteresis loop measurements. It has been found that with increasing Na doping for Cu, the transition temperature gradually increase while crystal lattice parameters slightly change. Magnetic hysteresis measurements have shown that the hysteresis loops of doped samples are greater than the undoped sample. In addition, significant enhancement has been observed in the J_c values of Na-doped samples, which were calculated from the M–H curves by using Bean’s critical state model.     

The effects of yttrium substitution in Bi-2223 superconductors

Bi_1.7?xY_xPb_0.3Sr₂Ca₂Cu₃O_y (x = 0, 0.05, 0.1 and 0.25) samples were prepared by a conventional solid state reaction method. The influence of Y on structural and superconducting properties has been investigated by XRD measurements, scanning electron microscopy (SEM), dc electrical resistivity, Vickers hardness and magnetic-hysteresis loop measurements. SEM micrographs show that the best surface morphology and largest grain size are observed for undoped samples. The critical transition temperatures of the samples decrease with the increase in the Y content. J_c values of the samples, obtained from Bean’s model, show that J_c decreases with increasing Y content. The mechanical properties of the samples, measured by Vickers hardness (H_v), were found to be load dependent.     

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.     

Comparison of Critical Current Density in Undoped,Glycine-doped,and Cu-and-Glycine-Co-doped MgB2 Synthetized from nm-Boron and μm-Boron

Nano-boron (800 nm) and μm-boron (25 μm) precursor were used to synthetize glycine-doped, Cu-and-glycine-co-doped, and undoped MgB₂ samples at 800 ^°C. The C substitution level caused by glycine doping, the MgO content, and the full width at half maximum of the (101) peak for MgB₂ phase were compared to evaluate the critical current density (J _c) of the six samples. The undoped sample from the nm-boron powder showed enhanced J _c over the entire field in contrast with those from 25-um boron, since the excess MgO in nm-boron prepared sample serves as effective pinning centers. On the contrary, due to the reduced MgO pinning centers as well as the increase of the grain size, the glycine-doped nm-boron sample only enhanced the J _c performance in the high-field region (H>4.5 T), while the low-field J _c values showed a considerable decrease. For the Cu-and-glycine-co-doped sample, the J _c performance is nearly without regard to the size of the boron precursor as the high-field J _c of the nm-B sample decreased a little, while the low-field J _c remained at the same level as that of the μm-B sample.     

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.     

Improved Transport J c in MgB2 Tapes by Graphene Doping

Graphene is a special form of carbon which can effectively enhance the critical current density J _c of MgB₂. In this work, a systematic investigation on the impact of sintering conditions and doping level was carried out for graphene-doped MgB₂ tapes. It is found that an appropriate addition level, i.e., 8 at% in this work, is very critical to obtain a high J _c in graphene-doped samples. The critical field and pinning force are improved obviously due to the graphene doping. The magnetic J _c of samples sintered at 800 °C with 8 at% graphene doping reached 1.78 × 10⁴ A/cm², at 5 T, 20 K. At the same time, the transport J _c was up to 2.38 × 10⁴ A/cm² at 10 T, 4.2 K. The lattice distortion caused by C substitution and residual C at the grain boundaries were thought to be the major factors affecting the J _c of graphene-doped MgB₂ samples.     

Relationship Between Annealing Time and Magnetic Properties in Bi-2212 Textured Composites

In this study, we report the physical and magnetic properties of Bi₂Sr₂CaCu₂O _x textured materials prepared by a LFZ melting technique and annealed for different times (60, 72, 96 and 120 h). SEM images of the annealed samples for 96 and 120 hours indicate very good alignment with the longitudinal rod axis. In all cases, X-ray diffraction patterns show that the Bi-2212 phase is the major one. The magnetization measurements have been carried out as a function of the magnetic field up to 9 kOe. J _c values of the samples were calculated by using the Bean model. The results indicate that the different annealing time has no significant effects on the T _c values but, significant change on the critical current values of samples, J _c, has been obtained for sample annealed at 96 hours. We also found that the maximum critical density of J _c is 5.5×10⁵ A/cm² at 10 K for the 96 hours annealed sample.     

Influence of Ce Substitution at Sr-Site on Superconducting Fluctuation Behavior and Infrared Absorption of Tl0.9Bi0.1Sr2?x Ce x Ca0.9Y0.1Cu1.99Fe0.01O7?δ (x=0–0.20) Ceramics

Ce substituted Tl_0.9Bi_0.1Sr_2?x Ce _x Ca_0.9Y_0.1Cu_1.99Fe_0.01O_7??? (x=0?C0.20) samples were synthesized to determine the effects of the higher valence ion substitution on superconductivity and structure of the Fe-doped Tl1212 derivatives. The normal state behavior for x=0 showed semiconductor-like behavior which gradually turned to metallic behavior with increasing Ce at x=0.05?C0.15. However, further substitution of Ce for x>0.15 turned the normal state to insulating behavior. The zero critical temperature, T _{c zero} increased from 65.4?K (x=0.05) to 71.0?K (x=0.10), but slightly decreased for x>0.10 indicating the optimum value of average copper valence was achieved at x=0.10. Excess conductivity analysis using the Aslamazov Larkin, AL and Lawrence?CDoniach, LD models revealed two-dimensional, 2D to three-dimensional, 3D transition of superconducting fluctuation behavior, SFB with the highest transition temperature, $T_{\mathrm{2D}\mbox{-}\mathrm{3D}}$ at x=0.10. FTIR analysis in conjunction with XRD results showed softening of FeO₂/CuO₂ planar oxygen mode from 610.5?cm^?1(x=0) to 605?cm^?1(x=0.20) which is suggested to be related to possible increase of inter plane coupling, J and this is supported by computed results based on the LD model. The enhanced J increases superconducting coherence length along c-axis, ?? _c (0), and hence lowers anisotropy, ?? resulting in enhanced superconducting properties.     

Magnetoresistance Study of Y3Ba5Cu8O18 Superconducting Phase Substituted by Nd3+ and Ca2+ Ions

Superconducting samples of type Y_3?x Nd _x Ba_5?x Ca _x Cu₈O₁₈ with 0.0 ≤ x ≤ 0.4 have been prepared via the solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) technique for phase analysis. The elemental content of the prepared samples was determined using particle-induced X-ray emission (PIXE). In addition, the oxygen content of these samples was obtained using non-Rutherford backscattering spectroscopy (RBS) at 3 MeV proton beam. The results indicate that these substitutions do not affect the orthorhombic structure, while they decrease the oxygen content of Y-358 phase. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature (T ₀). A slight change in the superconducting transition temperature (T _c) is observed for 0 ≤ x ≤ 0.1, and then it decreases linearly with further increase in x. The linear decrease in T _c is attributed mainly to the partial substitution of Ba²⁺ ions by Ca²⁺ ions rather than the partial substitution of Y³⁺ ions by Nd³⁺ ions. The effect of magnetic fields up to 4.44 kG on the electrical resistivity has been studied to investigate the vortex dynamics for the prepared samples. The experimental data, in the second stage of superconducting transition, fit well with the thermally activated flux creep (TAFC) model, and the activation energy U(B) shows a power law dependence on magnetic field as B ^?β . Also, the transition width is related to the magnetic field according to the relation ΔT α B ⁿ . The values of β and n are strongly dependent on the Nd³⁺ and Ca²⁺ ion substitution. The magnetic field and temperature dependence of the activation energy U(B, T) is found to be U(B, T)? ΔT B ^?η , where η = β + n. Furthermore, the critical current density at zero temperature, J _c(0), as a function of the applied field was calculated for all the prepared samples. The result shows an enhancement in J _c(0) of Y-358 phase at x equals 0.4 at different applied fields.     

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.     

Critical current density of (Tl1−x Hg x )Ba2Ca2Cu3 δ superconductor

Polycrystalline samples with superconducting transition temperatures higher than 130 K have been synthesized in the system Tl_1?x Hg _x Ba₂Ca₂Cu₃O_8+δ withx=0.0, 0.1, 0.3, 0.5, 0.7, and 0.9. The magnetization data of these samples as a function of applied magnetic field up to 5.5 T are measured in a SQUID magnetometer over a wide temperature range. These hysteresis curves are analyzed with the Bean critical-state model to estimate the intragrain critical current density,J _c . The results show that the values ofJ _c are comparable to the values of YBCO and the early reported pure Hg-1223 sample. The maximum value ofJ _c occurs in the (Tl_0.7Hg_0.3)-1223 sample with 5.9×10⁶ A/cm² at 10 K and 1.1×10⁴ A/cm² at 77 K in 1 T. Also, an exponential decay ofJ _c with temperature has been found in these Tl_1?x Hg _x7-1223 compounds, indicating the presence of weak links.     

The Effect of Gd Concentration on the Physical and Magnetic Properties of Bi1.7Pb0.3-xGdxSr2Ca3Cu4O12+y Superconductors

Bi–Pb–Gd–Sr–Ca–Cu–O bulk samples with nominal composition Bi_1.7Pb _0.3-xGd_xSr₂Ca₃Cu₄O_12+y (x=0.01, 0.05, 0.075, 0.10) were prepared by the melt-quenching method. The effects of different Gd doping on the structure have been investigated by electrical resistance, scanning electron micrographs, XRD, magnetization and magnetic hysteresis loop measurements. The magnetization measurements have been carried out as a function of magnetic field for fields up to 5 kOe at temperatures well below the zero resistance temperatures of the annealed samples. It has been found that the high-T_c superconducting phase, (2 2 2 3), is formed in the sample A with concentration x = 0.01, annealed at 840°C for 120 h. However, with increasing Gd³⁺ doping for Pb²⁺ the (2 2 2 3) phase gradually transforms into the (2 2 1 2) phase. The magnitudes of magnetization and initial susceptibility, | M | and | dM/dH|, and the hysteresis loop areas decrease with increasing Gd concentration x and/or temperature T. The fast decreases in | M|, | dM/dH |, and the hysteresis loop areas related to the superconducting volume, with increasing x and/or T seem to imply an existence of flux pinning centres in our samples. In order to support this implication the critical current densities J_c, of the samples, have been estimated at two fixed temperatures, 9 and 30 K. Our data have indicated that J_c decreases with increasing temperature and/or Gd concentration, as expected.     

Superconducting Properties of In Situ Mg1.05(B1−xCx)2 Doped with Melanin (C16H2O3N2) via Ultrasonication in Ethanol

In this paper, we have reported melanin (C₁₆H₂O₃N₂) as a dopant of MgB₂ for the first time. Here, the effects of melanin doping to the microstructures and superconducting properties of bulk MgB₂ are thoroughly studied from XRD, SEM, TEM, magnetization, and resistivity data. We have analyzed the critical current density (J _c), irreversibility field (H _irr), flux pinning, resistivity, lattice parameters, grain sizes, critical temperatures (T _c), and other microstructures of all the samples. We have varied the doping percentage according to the nominal atomic ratio of Mg_1.05(B_1?x C _x )₂, x=0,0.02,0.06,0.08,0.1. The J _c of all the melanin-doped samples are improved as compared to that of the undoped sample in high-field region (above 6 Tesla) at low temperature. The 8 and 10 % doped samples give the best results. The 8 % doped sample registers an enhancement of J _c by a factor of 3.6 at 7 T and 5 K as compared to that of the undoped one. But, in the low-field region, melanin doping reduces J _c. The H _irr shows remarkable enhancement at low temperatures below 20 K. The best value of H _irr was found for the 8 % doped sample. However, H _irr reduces at high temperatures above 20 K in all the melanin-doped samples. The volume pinning strength of all the doped samples is enhanced over the entire field range. Further improvement in superconducting properties can be achieved by further reducing the size of the melanin particles, increasing density, and improving the homogeneity of doping.     

Growth of (Cu0.5Tl0.5?x Hg x )Ba2Ca3Cu4O12?δ Superconductor with Optimal Carrier Density in CuO2 Planes and Fluctuation-Induced Conductivity

The growth of (Cu_0.5Tl_0.5?x Hg _x )Ba₂Ca₃Cu₄O_12??? (x=0, 0.25) superconductor with optimal carrier density in CuO₂ planes has been made possible by partial substitution of Hg at Tl sites in (Cu_0.5Tl_0.5)Ba₂O_4??? charge reservoir layer of (Cu_0.5Tl_0.5)Ba₂Ca₃Cu₄O_12??? superconductor. The fluctuation-induced conductivity (FIC) analysis has been carried out on resistivity vs. temperature curves by using Aslamazov?CLarkin (AL) theory and the results have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in order parameters. The microscopic parameters deduced from FIC analysis such as crossover temperature (T _o ), zero temperature c-axis coherence {?? _c (0)} and the interlayer coupling strength?(J) have been improved with Hg substitution. Also, 3D region has been shifted to higher temperature with Hg substitution. In order to verify the optimal carrier density in CuO₂ planes with Hg substitution, the post-annealing experiments have been carried out on these samples in nitrogen and air. These post-annealing experiments have caused under-doping of carriers from the optimal level resulting into a decrease in T _c (R=0) as well as the magnitude of diamagnetism.     

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.     

Microstructures of high-J c melt-textured YBa2Cu3O7−x /Ag superconductors

Silver has been previously added to the melt-textured YBa₂Cu₃O_7?x in order to increase the critical current density (J _c ) of these materials. However, the effect of this addition on theJ _c is presently unclear. The purpose of this study is to investigate the effect of silver on both critical current density and the microstructure of the melt-textured YBa₂Cu₃O_7?x superconductors by means of X-ray diffraction, optical polarized microscopy, and transmission electron microscopy (TEM). TheJ _c of the MTG YBCO/Ag samples is more than 10⁴A/cm² under the 5 kOe magnetic field. It has been shown that as the concentration of silver increases, the fraction of the 211 phase dispersed within the 123 matrix decreases. Therefore, theJ _c slightly decreases. These results, together with the effect of the 211 phase, dislocations, and other structure defects on flux pinning, are described in this paper.