Superconducting Properties of Ag and Sb Substitution on Low-Density YBa2Cu3O δ Superconductor

The effects of silver (Ag) and antimony (Sb) substitution on low-density YBa₂Cu₃O _δ (YBCO) superconductor were investigated. Two series of sample with a nominal composition of YBa_2?x Ag _x Cu₃O _δ and YBa_2?x Sb _x Cu₃O _δ where x=0.05, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 were synthesized and characterized. All Ag-doped samples showed metallic behavior at the normal state and T _C?onset was found at 90 K. T _C?zero decreased as the Ag concentration increased. Optimum Ag concentration was achieved at x=0.20 where T _C?zero has the highest value of 87 K and J _C at 70 K is 16.50 A/cm². For Sb-doped case with x≤0.30, the samples showed metallic behavior above T _C?onset while semiconducting behavior was shown for x≥0.40. The optimum Sb concentration was achieved at x=0.15 where T _C?zero is 85 K and J _C value measured at 70 K is 2.75 A/cm². T _C?onset and T _C?zero were found to decrease toward higher Sb concentration. The crystallographic structure transformed to tetragonal in Sb-doped samples of x≥0.30 while other samples remain orthorhombic.     

Fabrication of BSCCO Films on SrTiO3 Substrates Using Ultrasonic Spray Pyrolysis (USP) Technique

In this study, the BiSrCaCuO (Bi-2212) films on SrTiO₃ substrates were fabricated using an ultrasonic spray pyrolysis technique (USP). Structural, electrical, magnetic, and critical current density, J _c, properties of the films fabricated were investigated under different heat treatment conditions. XRD analysis showed that the films mainly consisted of the Bi-2212 phase, but the Bi-2223 phase was also detected. T _c values of the films were found between 81 K and 88 K, depending on the heat treatment conditions. J _c values of the films were calculated using the Beans’ equation. Highest J _c value was found to be 2.93×10⁵ A?cm^?2 at 5 K and 0 T for Film C. The results obviously showed that USP method is a very effective technique for fabrication of the HT _c films having high J _c values as well as its simplicity, low cost, and easily coating.     

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 Boron Doping on Transport Properties of?YBa2Cu3O7?y HTS

The nominally pure and boron-doped YBa₂Cu₃B _x O_7?y samples with B-doping level x varying between 0 and 0.15 were prepared by the solid state reaction. X-ray diffraction analysis shows that all the obtained compounds are single YBa₂Cu₃O_7?y phase. The small additives of boron in YBa₂Cu₃B _x O_7?y (x=0.025 and 0.05) do not essentially affect the critical temperature T _c and it remains near 90 K. The higher-level boron doping causes degradation of T _c and tail remains on the ??(T) curve for x=0.15 at 65 K. Lowest-level boron doping applied leads to a significant improvement in J _c compared to the undoped sample (from 100 A?cm^?2 for a control sample to 147 A?cm^?2 for a B-doped sample with x=0.025). Grain boundary critical current density and superconducting volume fraction decrease with increasing amount of added B₂O₃. The obtained results indicate possibility of boron dopant being entered into the lattice-sites.     

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.     

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.     

Synthesis of BSCCO Films on MgO (100) Substrate by Ultrasonic Spray Pyrolysis Technique

In this study, the HT _c Bi-2212 films were fabricated using the ultrasonic spray pyrolysis technique (USP). Structural/microstructural, electrical, magnetic, and critical current density, J _c , properties of the films fabricated were studied depending on heat treatment conditions in detail. XRD analysis revealed that a pure Bi-2212 phase formed in all the films, which is confirmed by SEM-EDX analysis. T _c values of the films were found near 75?K. J _c values of the films were calculated using Beans?? equation. Highest J _c value was found to be 3.36×10⁵?A?cm^?2 at 5?K and 0?T for film?A. The results obviously showed that the USP method is a very effective technique for fabrication of the HT _c films having high J _c values as well as its simplicity, low cost, easily coating.     

Effect of Bi2O3 Addition on the Single-Crystal BiSrCaCuO Whisker Growth

Bi-2212 superconducting whiskers have been fabricated by annealing a melt-quenched precursor using suitable heat-treatment cycles for Bi_3+x Sr₂Ca₂Cu₃O_8+?? where x=1 and 2. Approximately 1?C3 mm long whiskers were fabricated for x=1 and x=2 and their physical, electrical and magnetic properties were investigated. Crystallization activation energies of the materials were calculated according to Kissinger and Augis?CBennet method using the DTA data. Microstructural changes from glass to heat-treated glass-ceramic materials at different temperatures were investigated with SEM, EDX and XRD analyses. It was observed that the structure of the whiskers has high c-axis oriented single-crystalline Bi-2212 phase. The whiskers fabricated for x=1 and 2 showed very smooth surface without cracks and dislocations. T _c of the whiskers for x=1 and 2 were obtained to be 83.2 K and 79.8 K respectively. The change of magnetization with applied magnetic fields (M?CH) was investigated at three different temperatures, 10, 20 and 40 K, and J _c?mag was determined using the Bean model.     

Effect of Nb addition on magnetic,structural and superconducting properties of (Bi,Pb)-2223 superconductors

In this work, the effects of Nb₂O₅ addition with different ratios on the structural and magnetic properties of Bi_1.7?xPb_0.3Nb_xSr₂Ca₂Cu₃O_y (x = 0.00–0.20) superconducting samples were investigated. (Bi, Pb)-2223 superconducting samples were prepared by conventional solid-state reaction method. The phase formation, phase fraction and lattice parameters were determined from X-ray powder diffraction (XRD) measurements, the microstructure, surface morphology analyses of the samples were carried out using scanning electron microscope (SEM). Additionally, ac susceptibility measurements were done in order to determine the critical current density (J_c) and hole concentration (p) of the samples. AC susceptibility measurements were done at various ac fields (ranging from 20 to 160 A/m) to understand the effect of Nb addition on magnetic properties of Bi_1.7?xPb_0.3Nb_xSr₂Ca₂Cu₃O_y superconductor. Critical onset (T _c ^on ) and loss peak temperatures (T_p) were estimated from the ac susceptibility curves. It was observed from ac susceptibility measurements that the critical onset temperatures decreased from about 108–98 K with increasing Nb addition (x = 0.00–0.20). The imaginary part of susceptibility was used to calculate the intergranular critical current density (J_c) by means of the Bean’s model. X-ray diffraction analysis revealed that the samples consisted of a mixture of Bi-2223 and Bi-2212 phases as the major constituents and non-superconducting phase Ca₂PbO₄ as the minor. It was also shown from XRD measurements that volume fraction of high-T_c phase decreases with increasing Nb addition up to x = 0.20. The sample with Nb addition of x = 0.20 showed the highest volume fraction of Bi-2223 phase (86 %). When Nb addition was increased, the surface morphology and grain connectivity are found to degrade, the grain sizes decrease and porosity of the samples were observed to increase from SEM images except the sample with x = 0.20 Nb addition.     

Physical Properties and Diffusion-Coefficient Calculation of Iron Diffused Bi-2223 System

This study includes two parts: (I)?investigation of the effect of different annealing time (10?h, 30?h, and 60?h) on physical, superconducting, and microstructural properties of Fe-diffused Bi-2223 superconductor ceramics prepared by the conventional solid-state reaction method with the aid of the X-ray diffraction (XRD), scanning electron microscopy (SEM), dc resistivity (???CT) and transport critical current density (J _c ) measurements, and (II) determination of the diffusion coefficient and the activation energy of iron in the Bi-2223 system. In the former part, the zero-resistivity transition temperature (T _c ), phase purity, volume fraction, hole-carrier concentration, lattice parameters, surface morphology, texturing, crystallinity, grain connectivity, grain size, and room temperature resistivity values of the bulk samples are found and compared with each other. The results obtained show that both the zero resistivity transition temperature (T _c ) and transport critical current density (J _c ) regularly enhance with the increment in the diffusion-annealing time. The maximum T _c of 107±0.2 K and J _c of 50.0?A?cm^?2 are observed for the sample annealed at 830?°C for 60?h. As for the XRD investigations, according to the refinement of cell parameters done by considering the structural modulation, the enhancement in the diffusion-annealing is confirmed by both a decrease of the cell parameter a and an increase of the lattice parameter c of the samples, meaning that the greatest Bi-2223 phase fraction belongs to the sample annealed at 830?°C for 60?h. Moreover, SEM images display that the sample has the best crystallinity, grain connectivity, and largest grain size. Based on the results, the superconducting and microstructural properties improve with the increase in the diffusion-annealing time. In the latter part, Fe diffusion in the Bi-2223 system is examined in a range of 500?C830?°C by the variation of the lattice parameters evaluated from the XRD patterns. The temperature dependence of the Fe diffusion coefficient is described by the Arrhenius relation D=4.27×10^?5exp(?1.27±0.10) eV/k_BT, and the related activation energy of the iron in the Bi-2223 system is found to be about 1.27?eV. The relatively low value of activation energy obtained illustrates that the migration of the Fe ions primarily proceeds through defects such as pore surfaces and grain boundaries in the polycrystalline structure, leading to the improvement of the microstructural and superconducting properties of the samples, supported by the results of part?I. All in all, the aim of the present study is not only to analyze the role of diffusion-annealing time on superconducting and microstructural properties of Fe-diffused Bi-2223 superconductors, but also to find the diffusion coefficient and activation energy of Fe in the Bi-2223 system.     

Effects of MgO on the Electronic and Superconducting Properties in Succinic Acid (C4H6O4) Doped MgB2 Bulks

In this paper, we report the doping effects of succinic acid, C₄H₆O₄ (from 0 to 30 wt%) on the lattice parameter, critical temperature (T _c), critical current density (J _c), upper critical field (H _c2), and irreversibility field (H _irr) in MgB₂ superconductor. It was found that MgB₂ doped with 10 wt% C₄H₆O₄ and sintered at 900 °C exhibited excellent J _c above 10⁴ A?cm^?2 at 5 K and 8 T. Impurity scattering due to C substitution, improved crystallinity and the least amount of MgO in 10 wt% doped sample improves J _c very significantly. The MgO amount is rapidly increased in 20 and 30 wt% doped samples which causes a strong depression of J _c, H _c2, H _irr due to poor inter and intra-grain connectivity.     

Deformation of Mechanical Properties and Failure Behavior of Hays–Kendall Approach in Bi-2223 Superconducting Core After Eu Inclusions

Mechanical features of Bi_1.8Pb_0.4Eu _x Sr₂Ca_2.2Cu₃O _y superconductor samples (x=0, 0.01, 0.03, 0.05, 0.07, 0.1, and 0.3) are elaborated by traditional solid-state reaction route. The deformation of the mechanical properties belonging to the Bi-2223 crystal structure by Eu impurities with the aid of Vickers hardness (H _v ) measurements are conducted at different indentation loads from 0.245 N to 2.940 N for the first time. Further, the H _v values extracted from experimental results are investigated using five different models so as to demonstrate the role of Eu addition on Bi-2223 samples. Based on these results, we observed that the undoped sample reveals the indentation size effect (ISE) feature, whereas the Eu-doped Bi-2223 superconducting core demonstrates the reverse indentation size effect (RISE) nature. Additionally, it is attained that the models (Meyer’s law, EPD, and PSR) fail to determine the estimate of the microhardness with the applied load. Nonetheless, the HK approach is observed to be superior to other models for the pure sample showing the ISE feature, while the IIC model is found to be the most successful model for the explanation of the mechanical characteristics of the Eu impurities in Bi-2223 bulk ceramics obeying RISE nature.     

Effect of Postannealing Process on Bi2Sr2.1Ca0.9Cu2O8+δ Textured Superconductors

Bi-2212 samples prepared by the classical solid-state method have been grown from the melt using the Laser Floating Zone (LFZ) method. They have shown good grain alignment and transport critical current densities (J _c ). After postannealing processes designed to produce the Bi-2212 phase controlled decomposition, J _c values have been increased in an important manner. Maximum values have been achieved when samples were thermally treated at 680 °C for 168 h with improvements around 80 %, compared with the original textured samples. The results clearly indicate that postannealing processes, when adequately controlled, produce the formation of effective pinning centers which are responsible for the increase in the measured J _c values.     

Magnetocaloric study of monovalent-doped manganites Pr0.6Sr0.4−x Na x MnO3 (x = 0–0.2)

A systematic investigation of structural, magnetic, and magnetocaloric properties is reported for a series of monovalent sodium-doped manganites Pr_0.6Sr_0.4?x Na _x MnO₃ (x = 0, 0.05, 0.1, 0.15, and 0.2). Rietveld refinements of the X-ray diffraction patterns show that all powder samples are single-phased and crystallized in the orthorhombic structure with Pnma space group. Magnetic characterization and Arrott plot confirm the second-order phase transition at Curie temperature T _C decreasing from 310 K for x = 0 down to 272 K for x = 0.2. Magnetic entropy change is largest for x = 0 reaching 1.95 J kg^?1 K^?1 at 2 T field. This corresponds to a large relative cooling power of 102 J kg^?1 . Magnetic field sensitivity of magnetic entropy change and relative cooling power are analyzed and discussed.     

Effect of K substitution on Structural,Electrical and Magnetic Properties of Bi-2212 system

In this work, the effect of K in the Bi₂Sr₂Ca_1?xK_xCu₂O_8+y superconductor with x = 0.0, 0.05, 0.075, and 0.1, has been investigated. The samples were prepared by a polymer solution technique using polyethyleneimine, PEI. The effects of K substitution have been investigated by electrical resistivity (ρ?T), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, and magnetic characterizations. SEM and XRD results have shown that the Bi-(2212) phase is the major one independently of the K concentration. Moreover, the microstructure of samples is improved with K-concentration up to x = 0.075. From electrical resistivity measurements we have found that Tc is slightly higher than 91 K for K-concentrations up to 0.075, and then it decreases for higher doping for about 0.5 K. Moreover, this trend is maintained in the magnetic measurements in which the hysteresis loops are increased until 0.075 K-concentrations. The maximum calculated Jc, using Bean’s model, has been found at around 4.5 10⁶ A/cm² at 10 K and ~1,000 Oe for the 0.05 K doped samples.     

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.     

Dependence of Superconductivity and Its Weakly Linked Behavior in Bulk LaO1?x F x FeAs on F Doping

Samples of oxypnictide compound LaO_1?x F _x FeAs, with x=0.15 and 0.2 corresponding to over- and highly over-doped compositions, respectively, were prepared by solid-state reaction. We present their characterization by XRD and HRTEM, as well as resistivity ??(T), magnetization M(B) and microwave modulated absorption (MMA) response between 4.2?C300?K and applied fields B=0?C8?T. With change in?x, both the superconducting and magnetic behavior of the samples shows an interesting pattern. The ??magnetic anomaly?? at T??130?K, observed in M(T) for x=0, instead of getting totally suppressed shows a tendency to reappear in x=0.2 sample. Both samples typically show ??(300?K)>2.8×10^?3????cm and critical current density J _c(5?K, 1?T)<2×10⁷?A/m². The superconducting transitions as measured by ??(T) at B=0 are found broad for both x=0.15 and 0.2 samples with transition widths ??2.5 and 6?K, respectively. The slope |dB _c2/dT| (where B _c2 is upper critical field) determined by resistive onsets, for the x=0.15 and 0.2 samples, has values ??7.5 and 3.5?T/K, respectively. The superconducting state characteristics as reflected by ??(T,B), M(T), magnetic J _c(B) and MMA response are typical of the presence of weakly linked inter-grain regions in both the samples. Our HRTEM images of the x=0.15 sample show the presence of high angle (??43^°) grain boundaries, which are well known to limit the J _c in cuprate-based high T _c bulk materials.     

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.     

Fabrication and Properties of Ag–Ni Bimetallic Sheathed (Bi,Pb)-2223 Tapes

10-meter-long Ag?CNi bimetallic sheathed (Bi,Pb)-2223 tapes with outer nickel sheath and inner silver sheath have been successfully fabricated by the ??Powder in tube?? technique. Microstructure and phase evolution studies by means of SEM and XRD, as well as critical current density (J _c ) measurements have been performed. It is found that the nickel sheath and dwell time in the first sintering process have great influences on the texture evolution, phase transformation and J _c of the Bi-2223/Ag/Ni tapes. Mono-filament (Bi,Pb)-2223 tape with a J _c of 6656?A?cm^?2 and 61-filament tape with a J _c of 12420?A?cm^?2 are obtained. Although using composite bimetallic sheaths can reduce production costs and improve mechanical properties of the Bi-2223 tapes, the Bi-2223 content and J _c of Bi-2223/Ag/Ni tapes are relatively lower than that of traditional Bi-2223/Ag tapes. Meanwhile, due to higher Bi-2223 content and better alignment of Bi-2223 grains, tapes with 61-filament have higher J _c than mono-filament tapes.     

High-Magnetic-Field XMCD as a Novel Tool for the Study of Valence Fluctuation Phenomena—Application to Eu-based Intermetallic Compounds

X-ray magnetic circular dichroism (XMCD) in Eu-based valence fluctuating compounds, EuNi₂(Si_1?x Ge _x )₂ (x=0.82, 0.85) and EuNi₂P₂ are investigated at high magnetic fields up to 40 T. Distinct two XMCD peaks corresponding to different valence states, i.e., Eu²⁺ and Eu³⁺ states are observed in EuNi₂(Si_1?x Ge _x )₂ (x=0.82) and EuNi₂P₂ at the L absorption edges (2p→5d). This suggests that the Eu 5d electrons are magnetically polarized in the both valence states. Since Eu³⁺ state has nonmagnetic ground state J=0, where J is total angular momentum, finite XMCD of Eu³⁺ state can be closely related to the magnetic polarization of the conduction electrons that is induced by the local magnetic moments of Eu²⁺ (J=7/2) state through the strong hybridization.