BSCCO Samples Research Articles

Improving Superconductivity, Microstructure, and Mechanical Properties by Substituting Different Ionic Pb Elements to Bi and Ca Elements in Bi-2223 Superconductors

In this detailed study, the changes of microstructural, mechanical, and superconducting features of bulk Bi1.8Pb0.2Sr2.0Ca1.8Pb0.2Cu3Oy materials prepared at different milling time intervals (0.5 h ≤ x ≤ 8 h) were investigated in the most precise manner. The measurements of X-ray powder diffraction (XRD) and Vickers microhardness (Hv) were designed to scrutinize the bulk BSCCO samples. All the results of the measurements and calculations show that the characteristics responsible for the applications of the technology, industry, and engineering are significantly improved up to the 3 h milling time beyond that they tend to deteriorate. The enhancement of the characters is generally related to the transition from underdoped level of the (Bi, Pb)-2223 to the optimum level with the milling duration and this event approves that sufficient Pb nanoparticles penetrate the crystal structure. On the other hand, some of the reasons for the suppression in the superconducting properties are the presence of the porosity, disorder, defects, and the localization problem in the Cu-O2 consecutively stacked layers. In addition to those mentioned above, the other reasons are degradation in the crystallinity, reduction in the average crystallite size, and decrease in mobile hole concentration in the Cu-O2 layers. Similarly, the Pb inclusion rises the artificial random dislocations and grain boundary weak-links in the (Bi, Pb)-2223 superconducting system. Vickers microhardness measurements show that (Bi, Pb)-2223 bulk superconducting specimens exhibit typical indentation size behavior depending on the presence of both elastic and plastic deformations in the system. The results obtained from the hardness measurements have been analyzed by using Meyer law, PRS model, MPRS model, elastic–plastic deformation model, and Hays-Kendall approach. As a result, the Hays-Kendall approach was identified as the most successful model in describing the mechanical properties of the samples.

Joining condition dependency of joint resistance in ultrasonic welding of high-temperature superconducting tapes with indium

Ultrasonic welding (UW) is a candidate for easy and simple fabrication of lap joints of high-temperature superconducting (HTS) tapes. Our previous study applied UW to both silver-sheathed BSCCO tapes and copper-stabilized REBCO tapes with indium foil inserted in-between. However, the fabrication was performed with limited joining conditions and critical current, I C, degradation was confirmed in some of the BSCCO tape joints. In this study, we evaluated the joining-condition dependence of joint resistance and I C to improve UW-joined HTS tape performance. Various UW samples using BSCCO and REBCO tapes were prepared with different thicknesses of indium foil, ultrasonic vibration amplitude, joining pressure, joining time, and metal plate arrangement. The results showed that HTS tapes layered between metal plates on the top and bottom can avoid I C degradation even with higher joining energy, however thinner indium foil induced degradation in the BSCCO samples. Through this study, we found the value of joint resistivity only depended on the joining energy per unit joint area. The achieved joint resistivities were 14.0 nΩcm2 for the silver-sheathed BSCCO tapes and 36.1 nΩcm2 for the copper-stabilized REBCO tapes though it was strongly influenced by interface resistivity of the REBCO tape itself.

Effect of Rubidium Substitution on the Physical and Superconducting Properties of Textured High-Tc BSCCO Samples

In this research, the effects of rubidium (Rb) substitution on the microstructural, physical, and superconducting properties of Bi2Sr2Ca1-xRbxCu2O8 + y with x = 0.0, 0.025, 0.05, 0.075, 0.10, and 0.125 superconductor have, in detail, been studied. For this purpose, samples were prepared through the classical solid state reaction route, followed by directional grown using the laser floating zone technique and annealing. XRD measurements showed that all samples are composed of Bi-2212 phase as the dominant one, together with less amount of secondary phases. The crystal symmetries of samples were determined as pseudo tetragonal. SEM-EDX confirmed that Bi-2212 phase is the major one, with minor amounts of Bi2 + x(Sr,Ca)2O6 + d, (Sr,Ca)CuO2, CuO2, and CaO secondary phases. In magnetization versus temperature measurements, very sharp diamagnetic transition is observed. The critical onset temperatures, TC, for all samples are obtained around 90 K. From M-H measurement, it has been found that all samples have very large loop areas. By using the data from M-H measurements in the Bean model, the intragranular critical field, JC, has been determined. It has been found that the x = 0.05Rb sample shows the highest superconducting properties and the largest JC values (2.2 105 A/cm2 at 10 K). Moreover, the maximum pinning force, FPmax, at this temperature has also been obtained in x = 0.05Rb sample (8.5 108 Oe A/cm2).

Effect of K Substitution on Local Structure of Bi1.6Pb0.4Sr2−xKxCa2Cu3O10+δ System Probed by Extended X-Ray Absorption Fine Structure

The effect of K substitution on the local atomic structure of polycrystalline Bi1.6Pb0.4Sr2−xKxCa2Cu3O10+δ samples (BSCCO, x = 0, 0.02, 0.06, and 0.10) has been investigated. Unlike in other cases of alkaline substitution, the transition temperature Tc of the K-substituted BSCCO samples decreased systematically with increasing K content. Such decreasing Tc behavior supposedly originates from changes in the local structure of the BSCCO system. Analysis of extended x-ray absorption fine structure (EXAFS) data measured at both the Cu K-edge and Sr K-edge revealed that, as the K content was increased, the Cu–O and Cu–Sr bonds systematically extended, while the Sr–O bond distance gradually reduced. The corresponding mean-square relative displacement (MSRD), which represents the average local distortion, showed large alteration in both the CuO2 and SrO planes. Local atomic displacement due to K substitution seemed to weaken the interaction between the conduction layer and spacer layer, resulting in a drastic decrease of the Tc values. Overall, these experimental results provide important information to understand the correlation between the superconductivity and local structure of K-substituted BSCCO.

Effect of using two different starting materials (nitrates and carbonates) and a calcination processes on the grain boundary properties of a BSCCO superconductor

The influence of using two different starting materials (nitrates and carbonates) and calcination processes on the grain boundary properties of a BSCCO system have been investigated. Superconducting BSCCO samples with the chemical composition Bi1.64Pb0.34Sr2Ca2Cu3Oy were successfully fabricated by the sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy analyses have been used to study the phase formation and microstructure of the prepared samples, respectively. The DC electrical resistivity, critical current density, and AC susceptibility of the samples were measured. The XRD result showed that one can improve the phase formation of the Bi-2223 system by choosing suitable starting materials and the temperature of calcination. AC susceptibility and DC electrical resistivity revealed that the synthesis process improves the grain boundaries. The critical current density (measured in 77 K) increased from 100 A cm−2 to about 145 A cm−2. In fact, the critical current of the sample fabricated with a carbonates group and calcinated at 750 °C obtained 100 A cm−2, while a sample that was fabricated with a nitrates group and calcinated at 790 °C had the critical current of 145 A cm−2.

Effect of Carbon Nanotube Addition on the Superconducting Properties of BSCCO Samples Textured via Laser Floating Zone Technique

In this research, the effect of carbon nanotube (CNT) addition on the structural and superconducting properties of Bi2Sr2CaCu2Oy + x wt% CNT materials with x = 0, 0.5, 1, and 3 prepared by solid state method, followed by directional grown using the laser floating zone (LFZ) technique has been investigated. XRD measurements showed that all samples are composed of almost single Bi-2212 phase. SEM images proved that Bi-2212 phase is the major one, with minor amounts of (Sr,Ca)3BiOx, and Bi-2201 secondary phases. According to the magnetic results, carbon nanotubes decrease Tc values and significantly reduce the magnetic hysteresis loops area and the magnetic critical current density.

The influence of heat treatment on the microstructure, flux pinning and magnetic properties of bulk BSCCO samples prepared by sol-gel route

We study the combined influence of calcination and sintering temperature on the microstructure, superconducting and pinning properties of Bi1.6Pb0.4Sr2Ca2Cu3O10+θ (Bi-2223) prepared by the sol-gel route. Using several characterization techniques, including X-rays diffractometry and electrical transport measurements, we find that the powders calcined at 820°C often result in a crystal higher critical current density (Jc) compared those calcined at 830°C. The powder calcined at 820°C and sintered at 850°C (Bi-2223 820850) showed the best grain morphology and the largest magnetic hysteresis loop and a Jc equal to 12.94 × 105A/cm2, comparable to the best results found in the literature for Bi-2223. The enhancement in Jc for Bi-2223 820850 seems to be due to improved grain structure rather than creation of effective pinning centers, because the scaling behavior of flux pinning force densities indicates that the main pinning mechanism for all samples is normal point pinning.

The influence of re-pelletization and heat treatment on physical, superconducting, magnetic and micro-mechanical properties of bulk BSCCO samples prepared by ammonium nitrate precipitation method

Abstract The influence of re-pelletization and annealing time on the structural, magnetic, electrical and mechanical properties of Bi-based high temperature bulk superconductor have been investigated. All samples used in this study have been prepared by a wet technique denoted as ammonium nitrate precipitation method. The samples have been characterized by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), resistance vs. temperature ( R-T ), magnetic hysteresis ( M-H ) and hardness vs. applied load ( Hv-F ) measurements. Bi-2223 and Bi-2212 peaks as major phases have been observed with small amounts of impurities from XRD results. The microstructures of most samples show a plate-like granular form. The grain sizes have been investigated by SEM and XRD. The critical transition temperature ( Tc ) has been obtained from resistivity measurements in the range of 99–110 K, depending on the annealing time and re-pelletization. The calculated maximum critical current density (Jc), using Beans’ model, is around 12,000 A/cm2 at 10 K ∼ 0.2 T. Moreover, all prepared samples exhibit reverse indentation size effect (RISE) behavior and hardness increased with re-pelletization according to results obtained from mechanical measurements.

Monte Carlo simulation of the crossover from Bose glass to Bragg glass phase in layered BSCCO with columnar defects

Monte Carlo simulations of layered BSCCO samples are used to investigate the behavior of vortex matter at low fields, particularly in connection with the possible occurrence of a Bragg glass (BrG) phase at low density of columnar defects, a phenomenon characterized by the prevalence of short-range over long-range order. In this dislocation-free topological phase the translational order correlation function displays a power law decay. For magnetic induction B = 0.1 kG the analysis of the data for the first Bragg peak of the planar structure factor, the hexatic order parameter, and the Delaunay triangulation shows that, as the density of columnar defects is lowered, a crossover (or transition) from Bose glass to BrG phase takes place in this highly anisotropic high-T superconductor. Most importantly, an analysis of the low-temperature 3D vortex–vortex correlation function in terms of the structure factor, calculated via a saddle point approach and the use of the numerical data as input, provides clear-cut evidence of the power law decay of the divergent Bragg peaks in the BrG phase, a fundamental feature that was inequivocally verified only in isotropic compounds.

Superconducting and mechanical properties of the bulk Bi(pb)SCCO system prepared via solid state and ammonium nitrate precipitation methods

We have investigated the effect of preparation method on superconducting and mechanical properties of Bi(Pb)-2223 bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Solid-state reaction and ammonium nitrate precipitation methods have been used for fabrication of the bulk samples. In addition, the effect of annealing time on BSCCO samples have been studied. Structural, electrical, magnetic and microhardness analyses of samples are performed by the X-ray powder diffraction (XRD), the Scanning Electron Microscopy (SEM), DC resistivity, AC susceptibility and Vickers microhardness test. The critical transition temperature, phase purity, surface morphology and crystallinity of the prepared bulk samples are compared with each other. Elasticity (E), brittleness (Bi), fracture toughness (KIC) and yield strength (Y) values are also determined according to annealing time, applied load and production parameters of materials.

Josephson-induced hysteretical behavior of vortex matter in layered BSCCO samples with columnar defects: Bose glass phase and the melting process

We present Monte Carlo simulations of three-dimensional systems of vortex lines in the presence of random columnar defects using the Lawrence-Doniach model with BSCCO parameters. In particular, we study the structure factor and the vortex-vortex correlation length along the field (B) direction, for both intermediate and high fields. Two representative initial conditions at zero temperature (T) are used: the Abrikosov lattice and a random vortex lattice, mimicking possible configurations in a zero-field-cooled (ZFC) protocol, both characterized by smooth plane decoupling transitions (formation of pancake-like vortex structure), with exponential decay with T of the correlation length around the melting transition. The very relevant case of field-cooling (FC) from a melted configuration is also considered. In this case, as T decreases for intermediate B, the system evolves through states of an unpinned vortex lattice phase and metastable states of a phase of unpinned vortices in a Bose glass (BG) background; lastly, the system reaches a FC robust BG phase down to very low T. On the other hand, for high fields and under the ZFC protocol, the melting transition is practically concurrent with the discontinuous decoupling of planes; while, under FC, the vortex lattice decouples much before the melting transition. Indeed, we identify that the exchange between flux lines is the underlying mechanism for plane decoupling and the formation of a pancake-like vortex structure. We stress that the correspondent phase diagram B vs. T is in good agreement with previous experimental results in BSCCO.

Influence of isothermal hot pressing-doping treatment on the electrical and mechanical properties of bulk Bi-Sr-Ca-Cu-O

The influences of (isothermal hot pressing-doping) treatment on the microstructure, electrical and mechanical properties of Bi2Sr3-xCaxCu2O8+δ (BSCCO), x ranging from 0.0 to 2 are assessed. BSCCO pellets were prepared by isothermal hot pressing (IHP) technique. The experimental works in this study consists of dc electrical resistivity measurements for electrical and superconducting properties, microhardness tests for mechanical characteristics, powder x-ray diffraction (XRD) for phase analyses (phase ratio), differential thermal analysis (DTA) for melting behaviour and scanning electron microscopy (SEM) for microstructure investigations. The results indicated that the Ca2+ doping and isothermal hot pressing increased significantly the superconducting transition temperature (Toc), which promotes the formation of high-Tc phase. Additionally, Vickers microhardness (VHN), Young's modulus, fracture toughness, brittleness index and elastic stiffness coefficient were also improved. Moreover, IHP-Doping improved the microstructure and the density of the BSCCO studied samples. Microhardness was found to be load dependent. Otherwise, we evaluated the load independent hardness, Young's modulus, fracture toughness and brittleness index of BSCCO samples. The possible reasons for the observed enhancement in electrical and mechanical properties due to (i) the homogeneity of grain region distribution (ii) the enhancement of superconducting phases.

Strength of the phonon-coupling mode in La 2−xSr xCuO 4, Bi 2Sr 2CaCu 2O 8+ x and Y Ba 2Cu 3O 6+ x composites along the nodal direction

Despite the intensive efforts for determining the mechanism that causes high-temperature superconductivity in copper oxide materials, no consensus on the pairing mechanism has been reached. Recent advances in high resolution angle-resolved photoemission spectroscopies have suggested that a sizeable electron-phonon coupling exists as the principal cause for kinks in the dispersion relations (energy versus wave vector) of the electronic states. Here, we report on a systematic study about the influence of the electron-phonon coupling parameter “λ” in the electronic quasiparticle dispersions of a wide family of CuO composites. In particular, the influence of the doping level in the cuprate families, La 2−xSr x CuO 4, Bi 2Sr 2CaCu 2O 8+ x and Y Ba 2Cu 3O 6+ x over the dressing of the charge carriers, i.e., on the enhancement of the effective mass and the strength of the coupling mode for the nodal direction of the Fermi surface has been analyzed. Universal effects as the nodal kinks at low energies are theoretically reproduced, emphasizing the necessary distinction between the general electron mass-enhancement parameter λ ∗ and the conventional electron-phonon coupling parameter λ. Our analysis shows a remarkable agreement between theory and experiment for different samples and at different doping levels. In fact, in LSCO family, the coupling constant λ calculated consistently with the nodal kink dispersions, reproduces the observed critical temperatures T c , the gap ratio 2Δ 0/ k BT c , and other parameters which have been studied from a wide set of natural and empirical equations which have been used along the last decades. It will be concluded that the strong renormalisation of the band structure can be explained in terms of the phonon coupling mode, and must therefore be included in any microscopic theory of superconductivity, even for those materials in which the contribution to the pair formation can be less dominant. Nevertheless, in more anisotropic structures, simulations reducing the Coulomb effects to encourage the phonon mechanism reveal as seems unavoidable to consider additional coupling modes that justify the higher critical temperatures observed in BSCCO and YBCO samples.

Temperature dependence of the order parameter of cuprate superconductors

A model of charged hole-pair bosons with long-range Coulomb interactions and very weak interlayer coupling is used to calculate the order parameter of underdoped cuprates. Model parameters are extracted from experimental superfluid densities and plasma frequencies. The temperature dependence T is characterized by a “trapezoidal” shape. At low temperatures, it declines slowly due to harmonic phase fluctuations which are suppressed by anisotropic plasma gaps. Above the single layer Berezinski-Kosterlitz-Thouless temperature, T falls rapidly toward the three-dimensional transition temperature. The theoretical curves are compared to c-axis superfluid density data by Kitano et al. J. Low Temp. Phys. 117, 1241 1999 and to the transverse nodal velocity measured by angular resolved photoemission spectra on BSCCO samples by Lee et al. Nature London 450, 81 2007 and by Kanigel et al. Phys. Rev. Lett. 99, 157001 2007 .

Asymmetry of magnetization curves of textured BSCCO

The dependence of magnetization on magnetic field M(H) was measured for textured BSCCO samples in directions H‖c,H‖ab at different temperatures. Inclusion of the pinning parameter in the Valkov–Khrustalev model [V.V. Valkov, B.P. Khrustalev, JETP 80 (1995) 680] allowed to describe successfully the asymmetric M(H) dependencies. The temperature and magnetic field dependencies of critical current and pinning parameter for H‖c and H‖ab were estimated.

Analysis of the E-J Curve of HTS Tapes Under DC and AC Magnetic Fields at 77 K

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The evaluation of the electrical characteristics of technical HTS tapes are of the key importance in determining the design and operational features of superconducting power apparatuses as well as to understand the external factors which affect the superconducting performance. In this work we report the systematic measurements of the electric field versus current density, <formula formulatype="inline"><tex Notation="TeX">$E-J$</tex></formula> relation of short samples for three commercial HTS tapes (BSCCO-2223 tapes, with and without steel reinforcement, and YBCO-coated conductor) at 77 K. In order to get sensitive and noiseless voltage signals the measurements were carried out with DC transport current and subjecting the broad surface tape to DC (0–300 mT) and AC (0–62 mT, 60 Hz) magnetic fields. The voltage is measured by a sensitive nanovoltmeter and the applied magnetic field is monitored by a Hall sensor placed on the tape broad surface. The comparison between the <formula formulatype="inline"> <tex Notation="TeX">$E-J$</tex></formula> results obtained from the three tapes was done by fitting a power-law equation for currents in the vicinity of the critical current. For the current regime below the critical one a linear correlation of the electric field <formula formulatype="inline"><tex Notation="TeX">$E$</tex> </formula> against the current density is observed. The BSCCO samples presented the same behavior, i.e., a decreasing of <formula formulatype="inline"><tex Notation="TeX">$n$</tex></formula>-index with the increasing DC and AC magnetic field strength. Under AC field the decreasing slope of <formula formulatype="inline"> <tex Notation="TeX">$n$</tex></formula>-index is steeper as compared to DC field. The <formula formulatype="inline"><tex Notation="TeX">$n$</tex></formula>-index curve for the YBCO tape showed similar behavior for AC field, however under DC field in the 0–390 mT range exhibited a slight decreasing of the <formula formulatype="inline"><tex Notation="TeX">$n$</tex></formula>-index. </para>

Observation of unusual irreversible/reversible effects in a macroscopic cylindrical hole drilled in superconducting Bi–Sr–Ca–Cu–O

Current–voltage ( I– V) measurements were carried out for different current sweep rates (d I/d t) of transport current at zero magnetic field ( H = 0) and H ≠ 0 in a polycrystalline sample of Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O x (BSCCO) with a macroscopic cylindrical hole (CH) drilled. Similar measurements were also performed in the same BSCCO sample without CH for a comparison before drilling CH. For the same values of H, T, and d I/d t taken for both samples, it was observed that hysteresis effects appear in I– V curves upon cycling of transport current in upward and downward directions which contain the increasing and decreasing current values, respectively. However these effects which are seen in I– V curves of BSCCO sample with CH is more prominent than that of the BSCCO sample without CH. Further, the irreversibility effects in I– V curves of the BSCCO sample without CH disappears for H ≠ 0 exhibiting nearly a linear behaviour, whereas the hysteretic behaviour in I– V curves of the BSCCO sample with CH is still observed. This interesting behaviour could be evaluated that macroscopic cylindrical hole improves pinning properties of sample acting as a macroscopic flux pinning center for flux lines.

Addition of Ca-compounds nanoparticles in melt-textured Bi:2212

Superconducting BSCCO samples made by melt-texturing process were prepared with the addition of calcium zirconate and calcium silicate nanoparticles. Bi:2212 melt-textured composites prepared with 1 wt.% of either addition showed different behavior for the critical current density as a function of the applied field, indicating that for each additional compound the improvement can be associated to different enhancement mechanisms, such as the creation of pinning centers and the increase on the connectivity of the grains. The estimated pinning forces indicated higher values for the calcium compound containing samples.

Ratchet without spatial asymmetry: Controlling the motion of magnetic flux quanta using time-asymmetric drives

We report on vortex manipulation experiments which exploit the attractive interaction between ‘crossing’ pancake vortex (PV) and Josephson vortex (JV) lattices in Bi 2Sr 2CaCu 2O 8+ δ (BSCCO) single crystals under tilted magnetic fields. Deformations of the JV lattice allow us to indirectly move mutually interacting PVs. In dc-driven mode the in-plane field is varied slowly (adiabatically) while the PV density is monitored at different points in our single crystal BSCCO sample using a micro-Hall probe array. Variations in PV density as large as 40% have been demonstrated in this way and both enhancement and depletion are observed, depending on the location in the crystal, temperature and PV density. In ac-driven experiments, manipulation is achieved by applying trains of time-asymmetric (sawtooth) in-plane field pulses. We show how both flux focusing and defocussing can be readily achieved merely by varying the time-asymmetry of the drive. Our experimental results are well described by molecular dynamics simulations which consider the dragging of PVs by JVs.

Nondestructive interactions of carbon nanotubes with Bi 2Sr 2CaCu 2O 8

Experimental evidence is presented for the intercalation of carbon nanotubes (CNs) in polycrystalline Bi 2Sr 2CaCu 2O 8 (BSCCO) samples at the 12 wt.%-CN doping level, based on high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction measurements. Magnetization measurements performed on BSCCO samples with various CN doping levels do not indicate a change in the critical current density J c within experimental error. The embedding process did not have any detrimental effects on the superconducting critical temperature of any of the samples. In contrast to previous work, the temperatures and widths of the superconducting transition of all the samples were similar.