The Influence of Postannealing on Structural and Superconducting Properties of Bi-2212 Ceramics

The effect of postannealing on the structural and superconducting properties of Bi-2212 sintered ceramic samples prepared by the solid state reaction method has been investigated. Postannealing times were varied from 0 h to 192 h at 700 ^°C. Electrical resistivity studies showed that postannealed samples at 96 h have the lowest room temperature values while critical transition temperature does not change significantly. XRD data have shown that the Bi-2212 phase content does not change noticeably, independently of the postannealing length. In addition, J _c values, calculated from the hysteresis loops using the Bean’s model, increased with increasing the postannealing time until 48 h and decrease for longer ones.     

Role of Cerium Addition on Structural and Superconducting Properties of Bi-2212 System

This study examines the significant changes in the structural and superconducting properties of cerium (Ce) doped Bi-2212 superconductors via X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), electrical resistance and transport critical current density (J _c ) measurements. Ce concentration is varied from x=0.0 until 0.1 in a general stoichiometry of Bi_1.8Sr_2.0Ce _x Ca_1.1Cu_2.1O _y . Zero resistivity transition temperatures ( $T_{c}^{\mathrm{offset}}$ ) of the samples produced by the conventional solid-state reaction method are deduced from the dc resistivity measurements. Furthermore, the phase fractions and lattice parameters are determined from XRD measurements when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. The results show that $T_{c}^{\mathrm{offset}}$ and J _c at self-field of the samples reduced gradually with the increase in the Ce addition. Maximum $T_{c}^{\mathrm{offset}}$ of 79.7 K and J _c of 356.8 A?cm^?2 at 77 K are obtained for pure sample as against 44.6 K and 18.7 A?cm^?2, respectively, for the sample doped with 0.1?wt.% Ce. According to the refinement of cell parameters done by considering the structural modulation, the Ce doping is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample. As for SEM measurements, it is found that not only do the surface morphology and grain connectivity degrade but the grain size of the samples also decreases with the increase of the Ce addition. Moreover, EDX images indicate that the elements used for the preparation of samples distribute homogeneously and the Ce atoms enter into the crystal structure by replacing Cu atom. In addition, the variation of ??T _c ( $T_{c}^{\mathrm{onset}} -T_{c}^{\mathrm{offset}}$ ) is investigated for the presence of impurities and weak links between superconducting grains of the samples. The possible reasons for the degradation in microstructural and superconducting properties are also interpreted.     

Microstructure and Superconducting Properties of TaC-Doped Bi-2223 Ceramics

The microstructure, phase composition, and superconducting properties of Bi-2223 ceramics doped with 0.05–0.5 wt % TaC were investigated. The materials were heat-treated at 840°C in three steps (10 + 24 + 24 h). By optimizing the TaC content and heat-treatment conditions, the 77-K critical current density of the Bi-2223 ceramics in zero field was raised by a factor of 2.     

Variation of Mechanical Properties of Cr Doped Bi-2212 Superconductors

This study shows the influence of Cr inclusions on the mechanical properties of Bi_1.8Sr_2.0Cr _x Ca_1.1Cu_2.1O _y (Bi-2212) superconducting samples (x=0, 0.1, 0.3, 0.5, 0.7, and 1) prepared by conventional solid-state reaction route with the aid of the microhardness (H _v) measurements. Moreover, some characteristics such as Vickers microhardness, Young’s (elastic) modulus (E) and yield strength (Y), being responsible for the potential technological and industrial applications, are theoretically evaluated from the microhardness curves belonging to the samples and compared with each other. It is found that the load dependent microhardness values decrease nonlinearly as the applied load enhances until 2 N beyond, which the curves shift to the saturation region, confirming that all the samples exhibit the indentation size effect (ISE) nature. Further, the elastic modulus and yield strength values observed reduce with the enhancement of the applied load and Cr inclusions in the Bi-2212 matrix. The experimental findings are also analyzed by Meyer’s law, proportional sample resistance model (PSR), modified proportional sample resistance model (MPRS), elastic/plastic deformation model (EPD), and Hays–Kendall (HK) approach. According to the results obtained, the load independent microhardness values calculated by EPD, PSR, and MPSR models are far from the values of the plateau region; however, the HK approach is the most suitable model for the microhardness calculations of the samples prepared in this study.     

Structural and Superconducting Properties of Magnetically Doped Bi-2212 Textured Rods Grown by Laser Floating Zone (LFZ) Technique

In this work, we have applied the laser floating zone technique, a well-known method to produce highly aligned crystals and dense morphology, with improved transport properties, to obtain Bi₂Sr₂Ca₁Cu_2?x Ni _x O (x=0, 0.01, 0.03, 0.05 and 0.1) fibers of about 1.8 mm diameter ×12 cm length. Microstructural and magnetic properties of textured materials grown in the optimum conditions were analyzed through scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), powder XRD patterns, M–T and M–H loops. XRD analysis showed that addition of Ni at x=0.1 level caused the formation of small amounts of Bi-2201 phase. Thermal treatment has produced the agglomeration of Ni particles up to a few μm, detected by dot mapping EDX. Both T _c-onset and J _cmag values of the annealed rods decreased with the increasing Ni substitution rate, determined from the M–T and M–H loops, respectively.     

Effect of Compaction Pressure on Structural and Superconducting Properties of Bi-2223 Superconductors

In this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O _y and System II: Bi_1.6Pb_0.3Ag_0.1Sr₂Ca₂Cu₃O _y , respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150–750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T _c values for System I was determined to be in the 109–115 K with sample D having the highest T _c of 115 K while T _c varied in the 104–109 K range and sample B had the highest T _c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T _c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors.     

Dispersion Analysis of (Sr,Ca)In2O4 Inclusions in Bi-2212 Superconducting Ceramics

Dispersion analysis of second-phase inclusions in the Bi-2212/(Sr,Ca)In₂O₄ composite is carried out using relationships between the moments of particle size distributions. The results point the way for optimizing the microstructure of superconducting ceramics with the aim of raising their critical current density.     

Synthesis and Characterization of Bulk Bi-2212 Superconducting Ceramic Using Photopolymerization Reaction-Based Method

Journal of Superconductivity and Novel Magnetism - This study highlights the synthesis of Bi2Sr2CaCu2O8 (Bi-2212) superconducting ceramic using the photopolymerization reaction (PPR) and...     

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.     

Effect of Ce Addition on the Magnetoresistivity, Irreversibility Field, Upper Critical Field and Activation Energies of Bi-2212 Superconducting Ceramics

This study aims to analyze the effect of Ce addition on the microstructural, superconducting and physical properties of Bi_1.8Sr_2.0Ce _x Ca_1.1Cu_2.1O _y ceramics with x=0, 0.001, 0.003, 0.005, 0.01, 0.03, 0.05 and 0.1 via X-Ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-Ray (EDX) and magnetoresistivity measurements. The ceramics produced in this work are prepared using the standard solid-state reaction method. The zero resistivity transition temperatures (T _c), activation energies (U ₀), irreversibility fields (?? ₀ H _irr) and upper critical fields (?? ₀ H _c2) are determined from the resistivity versus temperature (R?CT) curves under dc magnetic fields up to 7?T. The results show that T _c and U ₀ values of the samples are found to decrease dramatically with the increase in the Ce-content and applied magnetic field. Moreover, XRD results indicate that all the samples contain the Bi-2212 phase only and exhibit the polycrystalline superconducting phase with less intensity of diffraction lines with the increase of the Ce addition. As for the results of SEM images, the texturing, crystallinity, grain size distribution, layered grain growth and grain connectivity are observed to degrade with the increase of the Ce doping. Besides, the irreversibility fields and upper critical fields are found to degrade as Ce doping increases. Penetration depths (??) and coherence lengths (??) are also discussed.     

Effect of Mn Addition on Structural and Superconducting Properties of (Bi, Pb)-2223 Superconducting Ceramics

This study deals with the effect of Mn addition on the structural and superconducting properties of Bi_1.8Pb_0.4Sr₂Mn _x Ca_2.2Cu_3.0O _y ceramics with x=0,0.03,0.06,0.15,0.3 and 0.6 by means of X-ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), resistivity, and transport critical current density (J _c) measurements. Zero-resistivity transition temperatures (T _c) of the samples produced via the standard solid-state reaction method are estimated from the dc resistivity measurements. Moreover, the phase fraction and lattice parameters are determined from XRD measurements while the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. It is found that T _c values are obtained to decrease from 109 K to 85 K; likewise, J _c values are observed to reduce from 3200 A/cm² to 125 A/cm² with increasing Mn addition. According to the refinement of cell parameters done by considering the structural modulation, the Mn addition is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample (Mn0). SEM measurements show that not only the surface morphology and grain connectivity are seen to degrade but the grain sizes of the samples are found to decrease with the increase of the Mn addition as well. The EDX results reveal that the elements used for the preparation of samples distribute homogeneously and the Mn atoms enter into the crystal structure by replacing Sr and Cu atoms. The possible reasons for the obtained degradation in microstructural and superconducting properties are also interpreted.     

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.     

Magnetoresistivity study on Cr added Bi-2212 superconductor ceramics with experimental and theoretical approaches

This study investigates the change of the superconducting and physical properties of Cr added Bi-2212 superconductor ceramics prepared by the conventional solid-state reaction method with the aid of magnetoresistivity measurements performed in a range from 0 to 7 T. The zero resistivity transition temperatures (T_c), irreversibility fields (μ₀H_irr), upper critical fields (μ₀H_c2), penetration depths (λ) and coherence lengths (ξ) are estimated from the magnetoresistivity curves. Furthermore, activation energy (U₀) values of the ceramics produced are found using thermally activated flux creep model. The results show that the T_c value decreases from 80.7 K (52.6 K) to 70.4 K (13.4 K) for the pure sample (the sample doped with 1wt% Cr) with the increasement in the applied magnetic field. Likewise, the U₀ values reduce dramatically with increasing applied magnetic field. In fact, the U₀ of 302 K is the smallest at 7 T applied field for the sample doped with 1wt% Cr. Additionally, the μ₀H_irr and μ₀H_c2 values decrease with the increase of the Cr addition. At absolute zero temperature (T = 0 K), the extrapolation of the μ₀H_irr(T) and μ₀H_c2(T) curves is used to obtain the μ₀H_irr(0) and μ₀H_c2(0) values of the samples. The inner (latter) is found to be about 85.87 T (191.21 T) T and 13.88 T (86.89 T) for the pure sample and the sample doped with 1wt% Cr, respectively. On the other hand, the ξ and λ values inferred from μ₀H_irr(0) and μ₀H_c2(0) are obtained to increase from 13.13 to 19.48 ? and 19.60 to 48.73 ?, respectively as the Cr addition level increases in the Bi-2212 bulk superconductor, presenting that the Cr doping suppresses the physical and superconducting properties of the samples as a result of the pair-breaking mechanism.     

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.     

Precursor Influence on the Electrical Properties of Textured Bi-2212 Superconductors

Several synthetic methods, solid-state, sol-gel and polymer solution methods, have been used to prepare prereacted precursors, as well as a vitreous material obtained by melt quenching. The influence of the starting powder characteristics on the phase formation, microstructure, T _c and J _c of Bi-2212 textured rods prepared by directional crystallization from the melt has been analyzed. In all the cases, high transport critical current values (higher than 3000 A/cm² at 77 K) have been obtained, independently of the precursor type. Samples obtained by the polymer route show improved T _c values, associated to a lower oxygen content.     

Environmental Degradation Effect on the Properties of Bi-2212 Highly Textured Rods

It is well know that H₂O and CO₂ (both present in the atmosphere) can react chemically with BSCCO superconductors, especially with the alkaline–earth cations, producing chemical degradation and reducing their performances. In this work, Bi-2212 highly textured rods were grown from the melt through a laser floating zone melting technique. In order to determine the influence of H₂O and CO₂ on these bulk textured samples, they were immersed in distilled water and in CO₂ saturated water. The evolution of the electrical and mechanical properties of these rods was determined as a function of the immersion time in both media and compared with their initial properties. It has been found that performance degradation was higher in distilled water than in CO₂ saturated one. Nevertheless, in any case, the degradation has been found to be not very important.     

Experimental and Numerical Analysis of Equivalent Elastic Properties for Bi-2212 and YBCO Conductors

For mechanical design and optimization of high field HTS magnet, predicting elastic properties of Bi-2212 and YBCO conductors was of great importance. Experimental, numerical, and analytical methods could be used to predict the elastic properties of Bi-2212 and YBCO conductors. Due to the limitation of experiment, the elastic properties along a length direction of Bi-2212 and YBCO conductors were obtained by a tensile test. In this work, the numerical homogenization based on a finite element method was used for predicting the other elastic constants of Bi-2212 and YBCO conductors, and the analytical homogenization was adopted for the further validation of the numerical results. Compared with the measured data, the prediction of numerical homogenized approach was feasible. The analytical and numerical results were basically in accordance with experimental data, demonstrating the feasibility of numerical approach to predict the elastic properties of Bi-2212 conductors as well as the two-step analytical method to predict the elastic properties of YBCO conductor.     

Microstructure and Transport Properties of Bi-2212 Prepared by CO2 Laser Line Scanning

A novel Laser Line Scanning method has been applied to process rectangular cross-section Bi-2212 monoliths containing 2.9 % Ag using a CO₂ Laser. Although previous work has suggested the use of nIR lasers (≈0.8–1.1 μm) for melt-processing metal oxide superconductors, the results obtained here demonstrate that mid-IR radiation from a CO₂ laser (10.6 μm) may be just as convenient for such a purpose while it enables processing large surface areas. The samples described here were processed at traverse rates ranging between 15 and 60 mm/h, exhibited a complex textured microstructure and yielded highest I _c values of 71 A at 77 K.     

The Influence of Na Addition on the Mechanical Properties of Bi-2212 Superconductors

In this work, the effects of Na doping on the mechanical properties of the samples are investigated by Vickers microhardness (H _v) measurements at room temperature. The highest microhardness values were obtained for Bi₂Sr₂Ca₁Cu_1.75Na_0.25O_y sample including x = 0.25 Na content. On the other hand, the experimental results of H _v were compared with true microhardness values (H ₀) calculated by some theoretical approaches such as elastic/plastic deformation (EPD), proportional specimen resistance (PSR), and the Hays-Kendall models. All theoretic calculations also show that the sample with x = 0.25 Na content has the best mechanical properties. In addition, stress-strain curves of samples indicated that all samples protect their elastic properties at all applied loads. Finally, the surface roughness measurements of all the samples were done, indicating that they strongly depend on the content of Na substitution.