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.     

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.     

Superconducting behavior of high-T c YBa2Cu3O7 thin films with BaO impurity produced by pulsed laser deposition

We have investigated the superconducting behavior of high-T _c YBa₂Cu₃O₇ (YBCO) thin films containing BaO impure phase produced by pulsed laser deposition. The thin films were characterized by the standard four-probe method, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD showed that all these thin films contained BaO impurity, with thec-axis normal to the surface of the substrates. The presence of impurity existed from substrate temperatureT _s of 727 to 796°C. When these thin films with BaO impurity were measured under the magnetic fields, it was found that the critical current densityJ _c increased slightly with increase in magnetic fieldB within the range ofB≤500 G, in the case ofB perpendicular to thec-axis of the film.     

Co-doping effects of Ca and Ce on the Superconducting Properties in Y1?x Ca x (Ba1?y Ce y )2Cu3O7?δ

A series of Y_1?x Ca _x (Ba_1?y Ce _y )₂Cu₃O_7??? (0??x??0.3, 0??y??0.3) polycrystalline superconductor samples were prepared using the solid-state reaction technique. The phase identification, crystal structure, and superconducting transition temperature (T _c ) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicted that the phase of samples changed from orthorhombic phase to tetragonal phase with increasing Ca concentration x and Ce concentration?y, and Ce did not form the superconducting structure. The lattice constants had a little change. The a-axis and c-axis lattice parameters increased. The b-axis lattice parameter decreased. The T _c and resistance had an obvious dropping tendency with increasing Ca and Ce concentrations. The transition width became sharper with the increase of x (=y). We drew a conclusion that the Ce-doping had an effect for strengthening the intergrain connectivity, and it counteracted the weakening effect of Ca-doping which introduced the hole causing a reduction in the interlayer coupling strength.     

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.     

Pulsed Laser Deposition of YBa2Cu3O7 Superconducting Film on MgO Templates Spray Pyrolyzed on Hastelloy C276

Pulsed laser deposition (PLD) was used to deposit YBCO on MgO-buffered C276 substrates in order to evaluate the quality of the deposited MgO films which were deposited by spray pyrolysis. The characterization of the thin films was done using scanning electron microscopy, atomic force microscopy, electron backscattered diffraction, X-ray diffraction 2??-scans, rocking curve (??-scans), phi scan, pole-figure measurements, and AC susceptibility. It was found that c-axis oriented YBCO films were grown on c-axis oriented MgO films which confirm that the deposited YBCO films copied the out-of-plane texture of the spray pyrolyzed MgO buffer. However, MgO and YBCO films have a very weak in-plane texture. The AC susceptibility measurements show that the YBCO films have a broad superconducting transition temperature which may be attributed to the weak in-plane texture.     

Synthesis of c-axis oriented AlN thin films on different substrates: A review

Highly c-axis oriented AlN thin films have been deposited by reactive sputtering on different substrates. The crystallographic properties of layered film structures consisting of a piezoelectric layer, aluminum nitride (AlN), synthesized on a variety of substrates, have been examined. Aluminum nitride thin films have been deposited by reactive pulsed-DC magnetron sputtering using an aluminum target in an Ar/N₂ gas mixture. The influence of the most critical deposition parameters on the AlN thin film crystallography has been investigated by means of X-ray diffraction (XRD) analysis of the rocking curve Full-Width at Half Maximum (FWHM) of the AlN-(0 0 0 2) peak. The relationship between the substrate, the synthesis parameters and the crystallographic orientation of the AlN thin films is discussed. A guide is provided showing how to optimize these conditions to obtain highly c-axis oriented AlN thin films on substrates of different nature.     

Critical Current Density and Intergranular Coupling Study of the Dysprosium Oxide Nanoparticle Added Bi1.6Pb0.4Sr2Ca2Cu3O y Superconductor

The dysprosium oxide nanoparticles’ addition effects on structural, DC electrical resistivity, critical current density, and AC magnetic susceptibility properties of polycrystalline Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O _y samples are investigated. X-ray diffraction (XRD) analysis showed that both (Bi,Pb)-2223 and Bi-2212 phases coexist in the samples having orthorhombic crystal structure. Bi-2223 phase concentration increases with increasing dysprosium nanoparticle concentration. DC electrical resistivity, critical current density (J _c), and AC susceptibility measurements reveal that adding dysprosium nanoparticles to bismuth–strontium–calcium–copper–oxide (BSCCO) improves superconducting properties of this system and enhances its critical current density due to the improvement of the grain connectivity with dysprosium nanoparticle addition.     

Transport Properties of Over-doped Epitaxial NdCeCuO Films

The transport properties of slightly overdoped Nd_2?x Ce _x CuO_4??? (NCCO) c-axis oriented thin films with x=0.17 have been investigated in the temperature range from 2.5 K to 300 K and in magnetic fields up to 6 T applied perpendicular to the CuO₂ planes. The films have been grown by a dc sputtering technique in on-axis configuration. They have been optimized on (001)-oriented SrTiO₃ substrates and successively annealed in pure Argon at 900?°C. Structural and compositional analyses were carried out by means of X-ray diffraction and scanning electron microscopy equipped with a wavelength dispersive spectroscopy detector. Current-voltage characteristics of the NCCO films have been measured and the temperature and the magnetic field dependence of the critical current density J _c(T,H) has been obtained. Finally, an increase of the low-temperature normal state resistance with the field has also been observed.     

Influence of preparation conditions on superconducting properties of Bi-2223 thin films

We report electrical transport properties of Bi₂Sr₂Ca₂Cu₃O_10+x (Bi-2223) superconducting thin films fabricated by pulsed-laser deposition on SrTiO₃ substrate. The aim of the study was to investigate the influence of preparation conditions such as deposition temperature (T _S), annealing time (t _A) and deposition rate (r). A critical temperature (T _c) as high as 110 K and critical current density (J _c) of 6·2 × 10⁶ A/cm² at 20 K were obtained for T _S = 760°C, t _A = 4 h and r = 1·5 Å/s. We also investigated the effect of Li doping on Bi-2223 thin films. Li intercalation results in high resistive onset transition temperature and the resistivity shows broadening in magnetic field that increases with field. The large broadening of resistivity curve in magnetic field suggests that this phenomenon is directly related to the intrinsic superconducting properties of the copper oxide superconductors. The sudden drop in J _c at relatively low magnetic field (H < 0·5 tesla) is due to the effect of Josephson weak-links at the grain boundaries.     

Effect of Tungsten (W) Substitution on the Physical Properties of Bi-(2223) Superconductors

The superconducting Bi_1.6Pb_0.4Sr₂Ca₂Cu_3?x W _x O_10+y (x=0.00, 0.05, 0.10, 0.15) bulk samples were prepared by the solid-state reaction method. The effects of W substitution on the BSCCO system have been investigated by the electrical resistivity (ρ-T), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), magnetic hysteresis and critical current density measurements. It has been found that the Bi-(2212) low-T _C phase is formed for all the substitution levels, together with the Bi-(2223) high-T _C phase. The results obtained from the XRD data show that the Bi-(2223) phase gradually transforms into the Bi-(2212) phase with increasing W substituting for Cu. In addition, from the magnetization measurements at the temperatures below the zero resistance temperatures of the samples, we have observed that a decreasing in magnitude of |M| with the increasing measurement temperature and W concentration. Therefore, the decreasing of |M| related to superconducting volume seems to imply an existence of flux-pinning centers in our samples.     

Double-sided YBa2Cu3O7−δ superconducting films prepared by laser ablation with a Si radiation heater

Double-sided superconducting YBa₂Cu₃O_7?δ thin films have been prepared by pulsed laser ablation with a Si radiation heater. Measurements show that those samples are of good quality with zero resistance temperatures of ≥90 K, critical current densities of ≥3 x 10⁶ A/cm² at 77 K and zero field, and 10 GHz microwave surface resistances of 370μΩ (second side) and 1.7 mΩ (first side), respectively. The X-ray diffraction patterns indicate that each side of the samples isc-axis oriented epitaxial YBa₂Cu₃O_7?δ film. Scanning electron microscopy (SEM) reveals that the surface of the films is rather smooth with no particle larger than 1 μm.     

The effect of Sm substitution on properties of Bi1.6Pb0.4Sr2Ca2? x Sm x Cu3O y superconductors

The effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples have been investigated in terms of X-ray diffraction (XRD), EDXRF (Energy Dispersive X-ray Fluorescent), magnetoresistivity, critical temperature, transport critical current density, and ac susceptibility measurements. The samples were prepared by the conventional solid-state reaction method. XRD patterns are used to calculate lattice parameters and phase ratio of the Bi-2223 samples. The volume fraction was determined from the intensities of Bi-2223 and Bi-2212 peaks. The room temperature XRD patterns of the samples showed the presence of Bi-2223 phase decreases with increasing the Sm content. We estimated the transition temperature of the samples from the resistivity versus temperature measurements in dc magnetic fields up to 0.6 T. We observed that transition temperature, T _c , and transport critical current density, , depend on the Sm substitution. They both decrease with increasing the Sm substitution. We extracted the peak temperature, T _p , and the pinning force density from our previous ac susceptibility measurements. The pinning force density decreased with increasing the Sm content. The possible reasons for the observed decreases in critical temperature and critical current density due to Sm substitution were discussed.     

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.     

Phase Diagram and Upper Critical Field of Homogeneously Disordered Epitaxial 3-Dimensional NbN Films

We report the evolution of superconducting properties with disorder, in 3-dimensional homogeneously disordered epitaxial NbN thin films. The effective disorder in NbN is controlled from moderately clean limit down to Anderson metal?Cinsulator transition by changing the deposition conditions. We propose a phase diagram for NbN in temperature-disorder plane. With increasing disorder, we observe that as k _F l??1 the superconducting transition temperature (T _c ) and normal state conductivity in the limit T??0 (?? ₀) go to zero. The phase diagram shows that in homogeneously disordered 3-D NbN films, the metal?Cinsulator transition and the superconductor?Cinsulator transition occur at a single quantum critical point, k _F l??1.     

Quantitative analysis of lattice disorder and superconducting transition in epitaxial YBa2Cu3O6.9 films

We show that the average lattice disorder in YBa₂Cu₃O_6.9 films grown by ion-beam sputtering is homogeneous and can be quantified by introducing the lattice coherence lengthr _c that is extracted from the width of X-ray diffraction rocking curves. The superconducting properties of the films are correlated withr _c ∶T _c decreases with increasing disorder forT _c ?10 nm, while the width of the resistive transition and the normal-state resistivity increase.     

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.     

Development of high-T c superconducting Bi-2223 tape joints

High-T _c superconducting joints between Ag-clad Bi-2223 tapes have been developed for persistent current applications. Two presintered tapes with one side of the silver stripped were lapped and then wrapped by a silver foil. The complex was uniaxially pressed followed by appropriate sintering to form a high-T _c superconducting tape joint. It was found that the ratio of critical currents through the joint to that of the tape,I _cj/I_c, depended on the uniaxial pressure and the sintering conduction. At liquid-nitrogen temperature 77 K,I _cj/I_c=99% has been achieved. Persistent current loops formed by Bi-2223 tapes have also been fabricated and tested. Joint resistance of a loop was determined to be ～4×10^?13 Ω between the decay time of 120 and 3600 sec.     

Effects of surface roughness of substrates on the c-axis preferred orientation of ZnO films deposited by r.f. magnetron sputtering

The c-axis preferred orientation of ZnO film is the most important factor for its successful application in piezoelectric devices. The effects of surface roughness of the substrate on the c-axis preferred orientation of ZnO thin films, deposited by radio frequency magnetron sputtering, were investigated. During sputtering, the oxygen content in the argon environment used was varied from 0 to 70% at a total sputtering pressure of 10 mTorr. Very smooth Si, smooth evaporated Au/Si, smooth evaporated-Al/Si, and rough sputtered-Al/Si were used as substrates. Their r.m.s. roughnesses, as measured by atomic force microscopy, were 1.27, 17.1, 21.1 and 65-118 Å, respectively. The crystalline structure and the angular spread of the (0 0* 2) plane normal to the ZnO films were determined using X-ray diffraction and X-ray rocking curves, respectively. The crystallinity and the preferred c-axis orientation of the ZnO films were strongly dependent on the surface roughness of the substrates rather than on the oxygen content of the working environment or on the chemical nature of the substrate.     

Superconducting behavior of high-Tc YBa2Cu3O7 thin films with BaO impurity produced by pulsed laser deposition

We have investigated the superconducting behavior of high-T _c YBa₂Cu₃O₇ (YBCO) thin films containing BaO impure phase produced by pulsed laser deposition. The thin films were characterized by the standard four-probe method, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD showed that all these thin films contained BaO impurity, with thec-axis normal to the surface of the substrates. The presence of impurity existed from substrate temperatureT _s of 727 to 796°C. When these thin films with BaO impurity were measured under the magnetic fields, it was found that the critical current densityJ _c increased slightly with increase in magnetic fieldB within the range ofB500 G, in the case ofB perpendicular to thec-axis of the film.