Enhancement of (Bi,Pb)-2223 HTS Formation by Boron-Doping

Influence of boron-doping on the superconducting properties of (Bi,Pb)-2223 HTS ceramics prepared in an alumina crucibles has been investigated. X-ray diffraction, resistivity, and AC susceptibility measurements were performed on the undoped and boron-doped compounds. Obtained results have shown that B₂O₃ addition in the Bi_1.7Pb_0.3Ca₂Sr₂Cu₃O _y precursor enhances the formation of high-T _c phase. The boron-doped samples with starting composition Bi_1.7Pb_0.3Ca₂Sr₂Cu₃B _x O _y (x=0.05 and 0.5) reveal significant improvement in the zero resistivity temperature compared to the undoped sample (from 72 K up to 100 K). Boron-doping level x=1.5 results in a substantial degradation of the (Bi,Pb)-2223 phase.     

Electrical Resistivity and Magnetoresistance Studies of?(Bi,Pb)-2223 Phase Substituted by Ru

Series of Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−x Ru _x O_10+δ , (Bi,Pb)-2223, superconducting samples (with x=0.0, 0.025, 0.05, 0.075, 0.1125, 0.15, 0.3, and 0.4) were prepared by a solid-state reaction technique. The structural and the superconducting properties of our prepared samples were investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), electron dispersive X-ray (EDX), electrical resistivity, and magnetoresistance measurements. The XRD showed the enhancement of (Bi,Pb)-2223 phase formation untiluntil x=0.05, beyond which a strong phase transition from (Bi,Pb)-2223 phase to (Bi,Pb)-2212 phase was observed. In addition, the superconducting transition temperature and the hole-carrier concentrations, determined from electrical resistivity measurements, increased as the Ru-contents increased untiluntil x=0.05. A systemic study of the magnetoresistance measurements for our prepared samples was carried out under applied weak magnetic fields started from 0.0 up to 4.4 kG, and their results were explained according to thermally activated flux creep and Ambegaokar and Halperin models. The calculated critical current density and upper critical magnetic field increased untiluntil x=0.05, and then decreased with further increased of Ru-contents. This indicated that the low-contents of Ru, 0.0<x≤0.05, can generate locally weak superconducting region that enhance flux pinning strength and hence improve the physical properties of (Bi,Pb)-2223 superconducting phase.     

Superconducting Properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Added (Bi,Pb)-2223 HTSs Prepared on Alumina Plates

Nominally pure and B₂O₃-added (Bi,Pb)-2223 HTS samples were synthesized in air on alumina plates. The influence of boron-doping as well as annealing conditions on the high-T _c 2223 phase evolution was studied using X-ray diffraction (XRD), resistivity and AC susceptibility measurements. The B₂O₃-added samples with starting composition Bi_1.7Pb_0.3Ca₂Sr₂Cu₃B _x O _y (x=0.05 and 0.5) reveal significant enhancement of 2223 phase formation compared to the undoped sample. Higher-level boron doping x=1.5 leads to the degradation of high-T _c 2223 phase.     

Possibility of Superconductivity of the 2212 Phase in the Bi(Pb)-Sr-Ce-Cu-O System

Synthesis of the Bi-2212 compound in the Bi-Sr-Ce-Cu-O system has been already known. But, there has been no report on superconductivity of the compound yet. We have prepared many Bi-2212 samples partially substituted by Pb for Bi in the Bi-Sr-Ce-Cu-O system. The nominal composition is (Bi_{2− y} Pb _y )Sr₂(Sr_{1− x} Ce _x )Cu₂O _z . Then, we have investigated possibility of superconductivity for the samples. As a result, we find that a sample with nominal composition of x=0.23 and y=0.1, which is of almost the single 2212 phase, shows an anomaly at about 70 K in addition to temperature dependence of the resistivity like a semiconductor. Furthermore, the sample also shows a decrease of magnetic susceptibility starting at about 70 K with decreasing temperature. These experimental results can be considered to result from superconductivity of the 2212 phase in the Bi(Pb)-Sr-Ce-Cu-O system.     

Effect of the fluctuation range of formation temperature on the preparation and superconductivity of Bi(Pb)2223 single-phase

Effects of the fluctuation range of formation temperature on preparation and superconducting properties of the Bi(Pb)2223 phase have been investigated in detail. Our results show that knowledge about the temperature distribution and fluctuation in the muffle furnace is necessary for preparation of the Bi(Pb)2223 single-phase. Single-phase samples from Bi_0.17Pb_0.3Sr₂Ca₂Cu₃O_y were obtained by a solid-state reaction in air at 835±5C. The best superconducting property of the as-prepared samples shows a one-step transition of a.c. susceptibility withT _c=109 K. Using this optimum sintering temperature and keeping the temperature fluctuation less than 5C, we have prepared pure Bi(Pb)2223 single-phase samples with good reproducibility.     

The Effect of Barium Doping on the Selective Structure of Bi-2223 Phase

The partial substitution of Sr by Ba in the two nominal compositions of Bi_1.8Pb_0.4Sr_2−x Ba _x Ca_2.2Cu₃O _y [x=0.0, 0.1, 0.2, and 0.3 (A group)] and Bi_1.66Pb_0.34Sr_2−x Ba _x Ca₂Cu₃O _y [x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 (B group)] have been investigated by resistivity, ac susceptibility measurements and by XRD and SEM analysis. In general, the nature of the temperature dependence of resistivity and susceptibility measurements indicate the presence of a superconducting transition between grains coupled by weak links. However, the XRD and SEM analyses show that the relative composition of initial elements used in Bi-(2223) is essential to the site that is selected by the Ba ions. In the A group, Ba doping up to x=0.1 will improve the phase formation of Bi-2223, and improve the superconductivity properties of the samples. In the B group, although Ba doping up to x=0.1 will enhance the phase formation of Bi-2223, it will decrease the coupling between the grain and the superconductivity properties of these systems. The presence of lower Tc phases will begin to appear for x>0.1, in both of these systems. The superconductivity properties and the phase formation of Bi-(2223) will decrease as the Ba concentration increases.     

Possibility of Superconductivity of the 2212 Phase in the Bi(Pb)-Sr-Ce-Cu-O System

Synthesis of the Bi-2212 compound in the Bi-Sr-Ce-Cu-O system has been already known. But, there has been no report on superconductivity of the compound yet. We have prepared many Bi-2212 samples partially substituted by Pb for Bi in the Bi-Sr-Ce-Cu-O system. The nominal composition is (Bi_2−y Pb _y )Sr₂(Sr_1−x Ce _x )Cu₂O _z . Then, we have investigated possibility of superconductivity for the samples. As a result, we find that a sample with nominal composition ofx=0.23 andy=0.1, which is of almost the single 2212 phase, shows an anomaly at about 70 K in addition to temperature dependence of the resistivity like a semiconductor. Furthermore, the sample also shows a decrease of magnetic susceptibility starting at about 70 K with decreasing temperature. These experimental results can be considered to result from superconductivity of the 2212 phase in the Bi(Pb)-Sr-Ce-Cu-O system.     

Doping of Bi-Sr-Ca-Cu-O Compounds with Mn

Formation of the superconducting phases Bi-2212 and Bi-2223 has been studied for samples with nominal composition Bi_aPb_bMn_cSr₄Ca₅Cu₇O _x (a + b + c = 4). The influence of the stoichiometric replacement of Bi and/or Pb by Mn on the electric and magnetic properties of the Bi-based superconductors has been studied. The partial substitution of Mn for Bi in the samples without Pb did not promote the growth of the Bi-2223 phase. The samples with double substitution Pb-Mn for Bi revealed a large amount of the Bi-2223 phase.     

Evolution of 2223 phase in the Bi2Pb0.6Sr2Ca2Cu3.1Oy system

The role of cationic ratios (Sr/Ca and Bi/Pb) in the evolution of high-T _c phase (2223) in samples prepared under different sintering conditions, starting with a composition of Bi₂Pb_0.6Sr₂Ca₂Cu_3.1O_y, has been investigated by employing energy-dispersive X-ray analysis, scanning electron microscopy and X-ray diffraction. As manifested by the observed decrease in Sr/Ca ratio, an increase in sintering temperature from 822 to 852 °C increases the disorder in Sr-O and Ca layers. The observed increase in the volume fraction of 2223 phase and the contraction inc-axis parameter have been explained on the basis of the observed decrease in Sr/Ca ratio. It thus appears that the disorder caused by the intersubstitution of Ca and Sr in SrO and Ca layers and partial replacement of Bi by Pb in the structure promote the evolution and growth of 2223 phase.     

Effect of high valency cations on the (BiPb)2Sr2Ca3Cu4O12+δ compounds

We have produced the (BiPb)₂V _x Sr₂Ca₃Cu_4−y Ti _y O_12+δ compounds by a melt-quenching method. For two different sintering times (185 and 192 hours), 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 and 192 h, with concentration x=0.2 and y=0.05. However, with increasing Ti doping the (2223) phase gradually transforms into the (2212) phase. The hysteresis loop areas decrease with increasing Ti concentration and sintering time. Our data have indicated that the critical current, J _c , decreases with increasing magnetic field.     

Effect of BN-Added Precursors on Phase Formation and Transport Properties of (Bi,Pb)-2223 HTS

(Bi,Pb)-2223 HTSs (high temperature superconductors) were synthesized from nominally pure (reference) and BN-added Bi_1.7Pb_0.3Ca₂Sr₂Cu₃O _y (BN) _x precursors (x=0,0.10,0.15, and 0.20) by the solid state reaction method using alumina crucibles. The influence of boron nitride addition on the phase formation kinetics and transport properties of (Bi,Pb)-2223 HTSs was studied using X-ray diffraction (XRD), resistivity and critical current density measurements. BN-added compounds reveal a significant enhancement in both the high-T _c 2223 phase formation and critical current density compared to the reference specimen.     

BPSCCO Superconductor with Addition of Ag2O Synthesized Under Electrical Field

Ag₂O-doped (1.2% wt.) nitrate freeze-dried powders (Bi : Pb : Sr : Ca : Cu = 1.7 : 0.3 : 2 : 2.5 : 3.5) were processed under an external electrical field and 17.5 MPa pressure at 800°C, for 4 min in vacuum. Final heat treatments (HT) were applied at 835–850°C for 70 h. in air (Bi, Pb)₂Sr₂CaCu₂O _x (2212-phase) was formed by electrical field processing in just 4 min. Electrical field application enhanced (Bi, Pb)₂Sr₂Ca₂Cu₃O _y (2223-phase) formation during final HT. Ag₂O additions to field sintered BSCCO ceramics increased the amount of 2223-phase and the zero resistance critical temperature (T _e(R=0)) by 4 k.     

Effect of annealing and quenching on superconductivity in Pb and Sb-doped Bi2Sr2Ca2Cu3O x

Samples of the series Bi_1·9−x Pb _x Sb_0·1Sr₂Ca₂Cu₃O _y withx=0, 0·1, 0·2, 0·3 and 0·4 were prepared by the solid-state route. The X-ray and d.c. electrical resistivity data on furnace-cooled and quenched samples are presented. Though the starting composition is 2223, the end products were multiphase with 4334 as the major phase. A superconducting transition withT _c=100K was observed in the pure 2223 sample after quenching. The furnace-cooled samples were metallic, while samples withx=0·1, 0·2 and 0·3 were superconducting after quenching. The amount of the 4334 phase decreases with increasing Pb content. Quenching seems to be favourable for the formation of the 4334 phase.     

Improving the Physical Properties of (Bi,Pb)-2223 Phase by SnO<Subscript>2</Subscript> Nano-particles Addition

In this work, the effect of SnO₂ nano-particles (40 nm) addition to the physical properties of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ superconducting phase was studied. (Bi, Pb)-2223 superconductor phase added by SnO₂ nano-particles was prepared by a conventional solid-state reaction technique. The SnO₂ nano-particles concentrations x varied from 0.0 to 2.0 wt% of the sample’s total mass. The prepared samples were investigated by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and electron dispersive spectroscopy (EDS) for analyzing phase formation and microstructure. Also, the electrical resistivity and transport critical current density, for investigated samples, were measured by standard dc four-probe method. Phase examination by XRD indicated that SnO₂ nano-particles enhanced the (Bi, Pb)-2223 phase formation up to x=0.4 wt%. On the other hand, the high concentrations of SnO₂ nano-particles retarded the phase formation. Granular investigation, from scanning electron microscope, showed that both number and size of voids decreased as x increased from 0.0 to 0.4 wt%. The superconducting transition temperature and transport critical current density were found to have optimal values at x=0.4 wt%. The enhancement rates in T _c and J _c were 12 and 58%, respectively, which had a maximum enhancement in both J _c and T _c for all investigated nano-particles.     

Role of Pb substitution and a study of synthesizing procedure for Bi-based superconductors

Bulk superconductors of the (Bi_1–x Pb _x )₂Sr₂Ca₂Cu₃O _y system have been synthesized by changing the Bi/Pb ratio. The effect of Pb substitution onT _c has been studied by standard d.c. resistivity measurements. An appropriate thermal procedure and time for the preparation of the 110 K phase has also been studied at length. The experiments indicate that the best results are obtained forx=0.2 and that a slow cooling process is necessary for a better control of the thermal process. Indexed X-ray diffraction patterns indicate the lattice parameters of low- and high-T _c phases asa _L=0.54004 nm,b _L=0.5445 nm,c _L=3.084 nm anda _H=0.5483 nm,b _H=0.5339 nm,c _H=3.772 nm, respectively. The observed superconducting behaviour is stable on thermal cycling between 77 and 300 K.     

A new model for the formation of high-T c phase in superconductive (Bi, Pb)2Sr2Ca2Cu3O x glass-ceramics

The formation mechanism of the high-T _c phase through the glass-ceramic route and the role of Pb on the formation of this phase have been investigated. It was found that a new compound with the chemical composition Pb₂Sr_{3 – x} Ca _x CuO _y (x = 1.8) precipitates at around 550C. This phase is stable up to 800C, where it begins to decompose, and at 850 C it completely disappears. It was found that some part of the released Pb diffuses into the 2212 phase leading to the formation of Pb-containing 2212 phase, (Bi, Pb)₂Sr₂CaCu₂O _x . On the other hand, an endothermic peak, probably arising from the melting of (Bi, Pb)₂Sr₂CaCu₂O _x phase or melting at grain boundaries containing Pb²⁺, was observed at 856C only in Pb-containing samples that were heat treated. The liquid phase attributed to the endothermic peak may enhance the formation of high-T _c phase (2223 phase). The growth kinetics for the high-T _c phase were analysed using the Johnson-Mehl-Avrami equation; the results indicate that the growth of the high-T _c phase is controlled by a diffusion process and the activation energy for its formation in the initial stage (shorter than 96 h) is 576 ± 45 kJ mol^–1.     

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.     

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.     

Interplay Between Diamagnetic and Ferromagnetic Phase in (Bi2223)1−y (LSMO) y Composites Thick Films

Thick films of ((Bi,Pb)₂Sr₂Ca₂Cu₃O _x )_1?y (La_0.7Sr_0.3MnO₃) _y [(Bi2223)_1?y (LSMO) _y ] composites (y=0.01, 0.03, 0.05) are deposited by means of a simple melting-quenching-annealing method onto (001)-oriented LaAlO₃(LAO) substrates. The constituent compounds Bi2223 and LSMO are prepared by standard solid-state reaction and sol–gel method, respectively. Measurements of the dependence of the magnetization on the temperature show the presence of superconducting and ferromagnetic phase below ～54 K and ～370 K, respectively. Current–voltage measurements on composites with y=0.01, 0.03 show that the superconducting critical current drop dramatically from I _c≈350 mA at T=15 K to zero at T≈0.5T _c (～25 K). The dependence of the magnetization on the external magnetic field applied in-plane or out-of-plane at 5 K displays well defined hysteresis loops, which correspond to the superconducting, diamagnetic phase. For T>T _c, the ferromagnetic loop of LSMO is observed. The critical current density, J _c, was determined for samples with y=0.01 and 0.05 by applying Kim’s model to the superconducting, diamagnetic hysteresis recorded at 5 K. The calculated values for J _c(B) resulted to be smaller than those obtained for individual bulk Bi2223 samples due, probably, to the presence of LSMO particles whose ferromagnetic domains compete with the superconducting diamagnetic phase.     

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.