Superconductive and Magnetic Properties of Bi2Sr2Ca2Cu3O10+�� Ceramics Doped by Pb

Among the superconducting phases of bismuth-based Bi?CSr?CCa?CCu?CO, compound Bi₂Sr₂Ca₂Cu₃O_10+?? (Bi-2223) is the most interesting because of its relatively high critical temperature (T _C =95?C110 K) and numerous applications. However, this phase is also known for its low stability and the difficulty of purifying parasites phases including the Bi-2212. To this end, the Pb used in relatively high proportions can stabilize, purify, and improve the further enhancement of T _C . The influence of Pb on structural, superconducting and magnetic properties has been extensively investigated in polycrystalline Bi_2?x Pb _x Sr₂Ca₂Cu₃O_10+?? ceramics (0<x<1). For low Pb amounts, structural analysis shows that the Bi-2223 phase is difficult to achieve without the Bi-2212 phase, and for high Pb content a large fraction of secondary phases containing Pb is detected. Our results confirm that the optimal Pb content for obtaining a Bi-2223 single phase is x=0.3, 0.4.     

Excess Conductivity Analysis of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ Added with Nano-ZnO and Nano-Fe2O3

Superconductor samples of type Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_10+δ added with nano ZnO and Fe₂O₃ were synthesized by the conventional solid-state reaction technique. The samples were characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and electrical resistivity measurements. Excess conductivity analysis of the investigated samples was carried out as a function of temperature using Aslamazov and Larkin (AL) model. The analysis showed four different fluctuation regions namely critical (cr), three-dimensional (3D), two-dimensional (2D) and short-wave (sw). The zero temperature coherence length along c-axis, effective layer thickness of the two-dimensional system and inter-layer coupling strength were estimated as a function of nano-oxides concentration. In addition, the thermodynamics, lower and upper critical magnetic fields as well as critical current density were calculated from the Ginzburg number N _G . It was found that the low concentration of nano-ZnO addition up to x=0.2 wt.% improved the physical properties of (Bi,Pb)-2223 phase. In contrary, these properties were deteriorated for x>0.2. These results indicated that the addition of a low amount of nano-ZnO during the final processing of (Bi,Pb)-2223 samples can be effectively improved the flux pinning ability, while the addition of a high amount of nano-ZnO decreased the volume fraction and increased the resistance of grain boundaries. Moreover, the addition of nano-Fe₂O₃ had a negative effect on the superconducting parameters of the (Bi,Pb)-2223 phase. This behavior was attributed to the decrease in the volume fraction of (Bi,Pb)-2223 phase with the increasing of nano-Fe₂O₃.     

Preparation, Structure, and Properties of (Bi,Pb)2Sr2Ca2Cu3O10 + δ Ceramics with Si3N4 Additions

The microstructure, phase composition, texture, and superconducting properties (T _c, T _c, j _c(T), and R(T) at H= 0 and 5 mT) of (Bi,Pb)₂Sr₂Ca₂Cu₃O_{10 +} ceramics (sintering at 840°C for 36 h) with ultrafine Si₃N₄ additions (0.05–0.2 wt %) are studied. The introduction of 0.05–0.1 wt % Si₃N₄ is shown to reduce the width of the superconducting transition by 2–3 K and to raise the critical current density at temperatures below 95 K.     

Effect of Mn on the Surface Morphological Properties of (Bi, Pb)2 Sr2Ca2Cu3?x Mn x O10+δ (Bi-2223) Superconductor

Samples of (Bi, Pb)₂Sr₂Ca₂Cu_3?x Mn _x O_10+?? (Bi-2223, x=0.0 to 0.30) were synthesized by a solid-state reaction route. The surface morphology investigated through scanning electron microscopy and atomic force microscopy (SEM and AFM) as a result shows that voids and grain sizes increase as the Mn concentration increases, and besides, nanosphere-like structures occur on the surface of the Mn-doped Bi-2223 sample. For x=0, compact granular structures of variously shaped thin grains and larger pores are observed in some local region. In the three-dimensional (3D) AFM view of the same surface the formation of the humps and roughness in some places can also be clearly seen, which is due to the formation of an oxide layer with different thicknesses, depending on the chemical composition of the phases. Besides the said features, two types of inhomogeneity have been observed in our investigations such as, first type, planar nanogranules of various sizes and, second type, closely packed planar rounded nanogranules.     

Thermal Conductivity Properties of Bi2-αTlαSr2Ca2Cu3O10+z Glass-ceramic HT c Superconductor Rods

The Glass rods with nominal composition of (Bi _2- Tl )Sr ₂ Ca ₂ Cu ₃ O _10+z , where =0.15, 0.25 and 0.35, have been prepared by melt casting technique. Preferably c-axis oriented grains were grown after the sintering process. The thermal conductivity (T) measurements were performed between 30K and 290K and calculations were made using Wiedemann-Franz law. The (T) values of the samples varied between 3.8 to 8.9 mW/cm.K and showed strong dependence to the heating temperatures and compositions. The best T _c and T _zero were obtained to be 122 K and 115 K respectively.     

Effect of ZrO2 Addition on Microstructure, Transport and Magnetic Properties of Bi2Sr2CaCu2O8+δ System

The influence of zirconium (Zr) addition to the Bi₂Sr₂CaCu₂O_8+δ (Bi2212) system on its phase formation, microstructure, transport, and magnetic properties is investigated. Samples have been characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy equipped with energy dispersive of X-ray analysis (SEM/EDX), and resistivity versus temperature measurement. The results show an increase of the critical temperature of superconductive transition T _c for x=0.01 and in all the samples containing Zr the Bi2212 phase is the majority. SEM observations show whiskers grains randomly distributed and microstructural change due to the addition of Zr. Resistivity measurement show that the temperature of the onset of transition T _c increases by 9 K for x=0.005, 0.02, and 5 K for x=0.01 of ZrO₂. An improvement of the normal state conductivity is obtained for the lowest content of Zr (x=0.005). In the normal state, all the samples exhibit a metallic behavior except the sample with x=0.01, which exhibit a semiconductor character.     

The Effect of Sn Substitution of Pb on Microstructure and Superconducting Properties of Bi–Pb–Sr–Ca–Cu–O Superconductor

The effect of substitution of Pb by Sn in Bi_1.6Pb_0.4?x Sn _x Sr₂Ca₂Cu₃ O _δ samples at x = 0.0, 0.1, 0.2, and 0.3 on the critical transition temperature and structural properties was investigated in this work. All the samples were prepared by the solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), resistance–temperature curve (R–T), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The Sn ⁴⁺ substitution of Pb ²⁺ caused significant changes in the properties of the samples. The formation of the (Bi, Pb)-2212 phase was stabilized and the T _c (onset) was improved at the x = 0.2 level of Sn ⁴⁺ substitution. The SEM micrographs have shown that the structure of the sample with x = 0.2 became more dense. However, samples with x = 0.1 and 0.3 have not shown zero resistance by EDS analysis because of oxygen deficiency.     

Fermi Surface and Superconducting Gap of Triple-Layered Bi2Sr2Ca2Cu3O10 + δ

We present a comprehensive study performed with high-resolution angle-resolved photoemission spectroscopy on triple-layered Bi₂Sr₂Ca₂Cu₃O_{10 +} single crystals. By measurements above T _C the Fermi surface topology defined by the Fermi level crossings of the CuO₂-derived band was determined. A hole-like Fermi surface as for single and double-CuO₂ layered Bi-based cuprates is found, giving new input to the current debate of the general Fermi surface topology of the high-T _C superconductors. Furthermore, we present measurements of the superconducting gap of Bi-2223 and show that there are clear indications for a strong anisotropy of the superconducting gap. The universal properties of this phase in comparison to the other Bi-based cuprates will be discussed.     

The Effect of Ru Substitution on the Thermal, Structural and Magnetic Properties of Bi3Sr2Ca2Cu3O δ Superconducting System

We have investigated the effect of Ru substitution on the thermal, structural/microstructural and magnetic properties of Bi-3223 system prepared using solid-state technique. The crystallization studies were made using DSC data with four different uniform heating rates. The formation temperature of Bi-2212 did not change significantly with increasing the Ru concentration; however, it was found that the thermal decomposition temperatures decreased. The activation energy for crystallization, E _a , decreased by increasing the Ru concentration. X-ray diffraction and SEM measurements showed that substitution of Ru for Bi caused significant changes in the crystal structure of the BSCCO material. A distorted and multiphase crystalline structure was observed. The M??T measurement exhibited that superconducting onset temperature (T _c ) decreased with increasing the Ru concentration in the system. The substitution of Ru for Bi caused the formation of ferromagnetic clusters in the materials, which destroyed the superconductivity in the system. Symmetric M(H) loops were obtained for lower Ru substitution, but in the case of high level substitution of Ru, a typical weak ferromagnetic-like hysteresis loop was found. It is believed that the Ru ions in the system are responsible for ferromagnetic behavior in the highly substituted materials.     

Improvement of Superconducting Parameters of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ Added with Nano-Ag

Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_10+δ superconductor samples were synthesized by the conventional solid-state reaction technique. Nano-Ag was introduced by small weight percentages (0.2, 0.4, 0.6, 1, and 1.5 weight %) in the final step of the synthesis process. Phase formation and microstructure were investigated using x-ray powder diffraction, differential scanning calorimetry, and scanning electron microscopy. The real elemental-content and oxygen-content were examined using particle induced X-ray emission (PIXE) and Rutherford backscattering (RBS) techniques, respectively. Electrical resistivity as function of the temperature was carried to evaluate the relative performance of samples. Moreover, Electric field-Current density (E–J) characteristic curves were measured at 77 K. The electrical and granular properties were greatly enhanced, indicating more efficient pinning mechanisms. An improvement of the critical current density of 229 % was obtained with x=0.6 wt.%, while the superconducting transition temperature is improved by 2.5 %.     

Dependence of the Structural, Electrical and Magnetic Properties of YBa2Cu3O7?δ Bulk Superconductor on the Ag Doping

The effects of Ag dopants on the superconducting properties of YBCO bulk samples, prepared under solid-state reaction method, have been studied by resistivity?Ctemperature (???CT), X-ray diffraction (XRD), scanning electron microscope (SEM), bulk density, AC susceptibility, DC magnetization measurements, and theoretical analysis. Small Ag substitutions (x??0.10) do not effect T _c of pure YBa₂Cu_3?x Ag _x O_7??? , while we observed small decreases of 1.5?K for larger doping levels (x??0.15). AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of DC bias field. The critical current densities (J _c ) have been estimated as a function of magnetic field from the magnetization data employing Bean??s critical state model. The increase in Ag amount (x) in YBa₂Cu_3?x Ag _x O_7??? (x??0.10) system effectively decreases the intragrain critical current density, which is attributed to the reduced connectivity between the grain boundaries. In the case of small additions (x=0.05), Ag atoms fill partly the pores, leading better crystallization of the grains.     

Observation of the Energy Gap above T c in (Bi,Pb)2Sr2Ca2Cu3O10+δ using Break-Junction Tunneling

Tunneling measurements of (Bi,Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀₊ have been carried out with break junction to study the gap feature above T _c = 106 K. The decreasing gap magnitude with increasing the temperature does not disappear at T _c for the most significant data. The gap-closing temperature is found to be T* 160 K.     

Superconducting and Magnetic Properties of Polycrystalline [(Bi,Pb)2Sr2Ca2Cu3O x ]1−x (La0.7Sr0.3MnO3) x Thick Films Grown Using MQA Method

Polycrystalline thick films with the nominal composition [(Bi,Pb)₂Sr₂Ca₂Cu₃O _x ]_1?x (La_0.7Sr_0.3MnO₃) _x (x=0, 0.01, 0.03, 0.05) were prepared by the melting-quenching-annealing (MQA) method on (001)-oriented LaAlO₃ (LAO) substrates. The XRD patterns show that the samples are composites consisting of (Bi,Pb)₂Sr₂Ca₂Cu₃O _x and La_0.7Sr_0.3MnO₃ particles with average grain sizes of ～60 and ～30 nm, respectively. From electric transport measurements, the superconducting onset temperature, T _onset, and superconducting critical temperature, T _c, ended up being ～80 and ～60 K, respectively. The depression of T _c may be attributed to the proximity effect between ferromagnetism and superconductivity. The M–H hysteresis loops indicate the coexistence of ferromagnetism and superconductivity in the films. The magnetic field dependence of the superconducting current density and the volume pinning force F _p=J _c×B were obtained by applying Bean’s model to the isothermal M–H loops.     

Mechanical Properties of Bi1.6Pb0.4Sr1.8Ba0.2Ca2Cu3?x Ni x O10+δ Superconducting System

Samples of Bi_1.6Pb_0.4Sr_1.8Ba_0.2Ca₂Cu_3?x Ni _x O_10+?? were prepared by solid-state reaction methods. Mechanical properties (Vickers microhardness, Young modulus, yield strength, fracture toughness and surface energy) by Vickers microhardness measurements have been carried out to examine the effects of Ni substitution. The results showed a deterioration of the mechanical properties with the enhancement of Ni content.     

Effect of Heat Treatments and Zr Doped on Superconducting Properties of Bi1.6Pb0.4Sr2Ca2Cu3O ?? Ceramics

The effects of heat treatments and the role of Zr have been studied using X-ray diffraction (XRD) method and resistance measurement technique equipment for the structural identification and determination of critical temperature, T _C. Generally, all samples displayed a normal metallic behavior above T _Conset. The values of T _C(R=0) have been found to decrease as Zr concentration increases. Heat treatments at 830 and 860???C; however, have increased the critical temperature, T _C in samples x=0.15 and x=0.20. The volume of the 2223-phase ratio on 2212-phase has decreased gradually toward Zr concentration. However, for samples x=0.15 and x=0.20, the ratio of 2223-phase was improved after applying heat treatment processes. The crystallographic structure remains in a tetragonal form where a=b??c. A?few Zr is still existed in sample x=0.15 and x=0.20 although after sintering and heat treated at 830???C implies that the excess Zr cannot incorporate into the crystalline structure of BSCCO system. After the heat treatment process at 860???C, all these Zr peaks suddenly disappeared, and hence improved the volume of 2223-phase.     

Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi_1.8Pb_0.44Sr₂Ca_2.2Cu₃O_x composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb)₂Sr₂CuO_x (2201), Ca₂PbO₄ (plumbate), (Bi,Pb)₂Sr₂CaCu₂O_x(2212), and (Bi,Pb)₃Sr₂Ca₂Cu₁O_x(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.     

Effect of High Valancy Cations on the Intergranular Pinning Energies of (Bi-Pb)2Sr2Ca2Cu3O10+δ Samples

In the present work, Bi-Pb-V-Sr-Ca-Cu-Ti-O bulk samples with nominal composition (BiPb)₂V _x Sr₂Ca₃Cu_4?y Ti _y O_12+?? with x=0.2 and y=0.1, 0.2 and 0.3 compounds have been prepared by the melt-quenching method. The magnetoresistance of the samples has been measured for different values of the applied magnetic field. Using the resistivity data, the upper critical magnetic field H _c2(0) at T=0?K was calculated. The coherence lengths at T=0?K were calculated from H _c2(0) values. The thermally activated flux creep model has been studied in order to calculate the flux pinning energies. The results showed that H _c2(0) varied from 152.5 to 60.4?T and the flux pinning energies varied from 515 to 184?meV at 0?T, with the content?y.