Bismuth-based Superconductors Research Articles

Spin–orbit coupling enhanced electron–phonon superconductivity in infinite-layer BaBiO2

The recent discovery of infinite-layer nickel oxide superconductors has highlighted the importance of first-principles simulations. We predict an infinite-layer bismuth oxide superconductor BaBiO2, which is isostructural to NdNiO2. In this work, electronic structure, lattice dynamics, and electron–phonon interaction are studied, with special attention paid to the influence of spin–orbit coupling (SOC) on the above-mentioned quantities. Our calculations show that the structure will be dynamically stable under pressure and induce superconductivity, whether SOC is considered or not. In addition, SOC will significantly enhance the electron–phonon coupling (EPC), resulting in an increase in EPC constant λ from 0.43 to 0.73. We further find that the Fermi surface nesting is partially responsible for its superconductivity. A strong SOC changes the Fermi surface and enhances the nesting, and the EPC becomes stronger. Our results propose a bismuth-based superconductor, demonstrating the importance of SOC for its superconductivity and providing clues for further experimental synthesis.

Effect of Optical Excitation on the Band Structure and X-Ray Absorption Spectra of BaBiO3-Based High-Temperature Superconductors: Ab Initio Calculation

The band structure, densities of states, and O K-edge X-ray absorption spectra have been calculated by the density functional theory method for BaBiO3-based perovskite high-temperature superconductors at different potassium doping levels in the ground and optically excited states. It has been shown that this approach including local structural inhomogeneities caused by doping and optical irradiation allows the correct description of changes in the properties of the electron subsystem near the Fermi level. It has been shown that doping is accompanied by the appearance of hole carriers on the Bi6s−O2pσ*. hybridized orbital in agreement with the model of the electronic structure of bismuth-based high-temperature superconductors in terms of a spatially separated Fermi-Bose mixture. It has been found that the band structure for the excited state of the undoped compound is equivalent to the band structure of the tight binding model for a cubic lattice. The results are important for the preliminary analysis of time-resolved X-ray absorption spectra on an X-ray free electron laser at femtosecond optical excitation.

Properties of Bismuth-Based Superconductors Precursors obtained under the influence of the Radiant Flux

The results of the study on the synthesis of high-temperature superconductors in the system Bi-Pb-Sr-Ca-Cu-O based on amorphous precursors were considered in this article, and were obtained under the influence of the radiant flux. A study of the elemental composition of amorphous precursors has showed the presence of 20 at.% superstoichiometric oxygen. The increase in the rate of formation of the superconducting phase and the high texture of the particles in the ceramic samples along the plane [00I] were established. The synthesized samples were composed of superconducting phase Bi1,7Pb0,3Sr2Ca2Cu3Oy. Research has established a presence in samples of HTSC phase with Tc up to 181K.

Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

Angle-resolved photoemission spectroscopy (ARPES) is typically used to study only the occupied electronic band structure of a material. Here we use laser-based ARPES to observe a feature in bismuth-based superconductors that, in contrast, is related to the unoccupied states. Specifically, we observe a dispersive suppression of intensity cutting across the valence band, which, when compared with relativistic one-step calculations, can be traced to two final-state gaps in the bands 6 eV above the Fermi level. This finding opens up possibilities to bring the ultra-high momentum resolution of existing laser-ARPES instruments to the unoccupied electron states. For cases where the final-state gap is not the object of study, we find that its effects can be made to vanish under certain experimental conditions.

Study of Superconducting Properties in Bismuth-Based Cerium Doped High-T c Superconductors

Superconductivity in bismuth-based high-Tc superconducting materials attracts the researchers for their unique properties. Bismuth-based superconductors commonly called BSCCO have great importance among the superconducting family. These are divided into three phases among them 2223 phase is highly studied in order to investigate its superconducting properties by substitution of different elements. We have studied the substitution of cerium (Ce) on the calcium site of bismuth-based Bi(Pb)Sr(Ba)-2223 high-Tc superconductor. The nominal compositions of Bi1.6Pb0.4Sr1.6Ba0.4(Ca1−xCex)2Cu3Ox ceramic superconductor were prepared by the sol–gel method. X-ray diffraction (XRD) was done at room temperature for structural analysis and different parameters were calculated. Surface morphology was done by scanning electron microscopy (SEM). DC resistivity measurements for the transition temperature of synthesized superconducting samples were taken by the standard four-probe method, apparatus for which was developed in our laboratory. Current density measurements were also taken by the same apparatus. The synthesized superconducting samples were also characterized by thermogravimetric analysis (TG) and Fourier transformation infrared radiations (FTIR). It is observed that the substitution of cerium on the calcium site favors the formation of single high-Tc 2223 phase.

Synthesis and enhancement of current density in cerium doped Bi(Pb)Sr(Ba)-2 2 2 3 high Tc superconductor

Bismuth based superconductors (BSCCO) having 2223 phase is highly carried by the researchers to study the structural and other properties. The effect of substitution of cerium element on calcium site of bismuth based Bi(Pb)Sr(Ba)-2223 high Tc superconductor for the enhancement of superconducting properties like critical temperature(Tc) and critical current density (Jc) are studied. The nominal compositions of Bi1.6Pb0.4(Sr1−yBay)2(Ca1−xCex)2Cu3OY (where x=0.0, 0.1, 0.2, 0.4 and y=0.0, 0.4) ceramic superconductor were prepared by wet chemical method. Stoichiometric amounts of Bi2O3, PbO, Sr(NO3)2, BaCO3, CaCO3, CuO and CeO2 were used as starting materials. The effect of substitution of cerium on calcium site and its effect on current density of Bi-2223 phase were studied. To study the structural morphology and surface analysis X-ray diffraction (XRD) and scanning electron microscopy (SEM) was done. It is observed that with the substitution of cerium on calcium site not only the phase pure material is obtained but also the current density increases.

Cutting-Edge Technology of Bismuth-Based High-Temperature Superconducting Wires for Application in Energy- and Environment-Related Fields

The first bismuth-based superconductor was discovered by Dr. Maeda of National Research Institute for Metals (currently, National Institute for Materials Science) in 1988. Since then, Sumitomo Electric Industries, Ltd., has been attempting to improve the fabrication method of superconducting wires and to develop products applying bismuth-based superconductors. As a result, the length of wires that can be fabricated has steadily increased as well as the wire performance, and these achievements have led to the practical use of prototype products and demonstration projects worldwide. Bismuth-based superconducting wires were established as an industrial material along with the development of an over pressure sintering method. In addition to this industrial accomplishment, these wires are now ready for practical use in application fields such as power cables and large-scale motors for ships. Superconductivity is an ultimate energy-saving technology, and its practical utilization is expected to contribute to the reduction of CO2 emission and the prevention of global warming.

Thermoelectromotive force in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductor

The temperature dependence of the thermoemf in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductors is studied. The thermoemf is positive at high temperatures (T > 300 K) and negative at low temperatures. As the temperature decreases, the thermoemf reaches a maximum slightly above Tc and then sharply drops to zero. The results can be explained in the framework of the two-band theory with a linear temperature term.

Current-voltage characteristics of a foamed Bi1.8Pb0.3Sr2Ca2Cu3O x high-temperature superconductor with fractal cluster structure

The influence of the structure of foamed polycrystalline bismuth-based superconductors on their critical currents and current-voltage characteristics is studied. It is found that superconducting foams have a fractal structure, and the fractal dimension of the boundary between the normal and superconducting phases is estimated. The magnetic and transport properties of superconducting foams are investigated, and the current-voltage characteristics are obtained in a wide range of currents. The effect of percolation phenomena on vortex pinning in a foamed superconductor is considered. The current-voltage characteristics of the superconducting foams at the beginning of the resistive transition are found to be in good agreement with a model in which a magnetic flux is assumed to be trapped in the fractal clusters of a normal phase.

Polarization effects in photoemission disentangle the origin of the shadow bands in Bi-based superconductors

Angle-resolved photoemission spectroscopy has been used to investigate the origin of the shadow bands present at the Fermi surface of bismuth-based superconductors. Momentum distribution curves along the $\ensuremath{\Gamma}Y$ high-symmetry direction and Fermi surface maps measured on ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ (Bi2212) single crystals with two different doping levels have revealed that the shadow bands and the main bands have different initial state symmetry. This result implies that the orthorhombicity exhibited by these materials cannot be responsible for their emergence at the Fermi surface.

Morphological Effects of Grinding on Bismuth-Based Cuprate Superconductors

Morphological changes of bismuth-based cuprate superconductors, such as the 2223 phase, via a small mechanical force were studied mainly by means of high-resolution transmission electron microscopy and atomic force microscopy. Even light mechanical grinding of the sintered 2223 samples led to the formation of superfine particles that had a width of {approximately} 5 nm. Moreover, the authors found first that the superfine particles had a discrete thickness of odd numbers of a half unit length c/2 of the 2223 phase, e.g. 1.9 nm, 5.6 nm, and so on. The formation of the superfine particles was due to cleavage at Bi-O double layers that were bound weakly to each other in a unit cell.

Computer simulation of the load characteristics of low-temperature thermoelectric coolers

The load characteristics of low-temperature thermoelectric coolers have been studied by means of computer simulation using the differential equation of stationary thermal conductivity with temperature-dependent kinetic coefficients. Based on the obtained results, the branches of characteristics of the thermoelements employing bismuth telluride and a bismuth-based superconductor are compared.

A new approach to transport theory of high Tc bismuth-based ceramic superconductors

A new transport theory for high temperature superconductors is propos#ed and supported with extensive calculations. The Cooper-pairs while remaining on a pseudo Fermi surface behave like weak Fermions. When the Cooper-pairs become free they behave as spinless bosons. The polarons and bipolarons are highly localized quantum states with virtually no gap existing in between them and are considered as bosons with nondegenerate spining. The binding energies of Cooper-pairs both in a weak Fermion system and for a spinless boson are calculated. A kind of a semimetallic softening transition is responsible for high temperature superconductivity and is temperature independent. There is no electron–phonon coupling for high temperature superconductors. High temperature ceramic superconductors before the onset of superconductivity are found to be Mott–Hubbard dielectric insulating materials.

Photoemission Electronic States of Thallium- and Bismuth-Based Superconductors

2,3 L2,3 Auger spectra. Both Cu 223 3/2 and Cu 223 1/2 core-level lines consisted of two spin-orbit split main lines accompanied with the two satellite lines. The charge transfer energy Δ from the oxygen ligand to the copper 3d 9 states and the hopping integral t were estimated from the energy separation between the main line and the satellite line taking advantage of the local cluster model calculations and their extension to high-temperature superconductors. The Coulomb correlation on-site energy Udd of two electrons in the same copper orbital and Upp of two electrons in the oxygen orbital as well as the correlation energy Uc d of the 2p core hole - 3d electron interaction have been estimated from the Auger electron spectra and the valence band spectra. They are: Uda = 6.0 ± 0.5 eV, of Upp # 10 ± 1 eV and of (lcd #8.0 ± 0.5 eV nearly the same for both the Tl- and Bi-compounds. We conclude that these compounds are the charge transfer strongly-correlated metals. PACS numbers: 74.72.-h, 79.60.-i

Corrosion of bismuth-based superconductor wires by some atmosphericagents

Superconducting wires (SWs) were previously prepared in our group byheat treatment of bismuth-based superconductor coatings on a metal core.This paper presents an analysis of the corrosion process by some atmosphericagents on the SWs. SWs with different concentrations of a(Bi, Pb)-2223 phase have been exposed to water vapour saturated air, to purewater vapour or to dry carbon dioxide. Each of these atmospheric agents wasfound to act differently on the SWs. However, all the studied corrosionprocesses present a high sensitivity to the concentration of the (Bi, Pb)-2223phase. For a higher concentration of this phase, the SWs are lesssensitive to atmospheric agents.

Stress induced change in hole concentration in superlattice films of bismuth-based oxide superconductors

Superlattice films of bismuth-based oxide superconductors, for instance (2234)/sub 1/(2212)/sub 1/ and (2245)/sub 1/(2201)/sub 1/, have been synthesized by sequential sputter deposition of bismuth oxide, strontium-copper-oxide and calcium-copper-oxide monolayers. Crystal structures, superconducting transition temperatures and hole concentration of the films were studied by X-ray diffraction, Meissner effect and Hall effect measurements. It was observed that the superconducting transition temperatures were enhanced by forming superlattice films of overdoped (2212, 2201) and underdoped (2234, 2245) phases. The results can be understood by stress induced changes in the hole concentration between the overdoped and the underdoped phases originating from the epitaxial (lattice matching) formation of the superlattice films.

Manufacture of ultrafine BiPbSrCaCuO powder by an in situ nanometre reaction process

A new method has been developed for the manufacture of the bismuth-based superconductor precursor powder BiPbSrCaCuO for fabrication of high- Ag/Bi(2223) tape. The new method consists of two main stages. First, nanoparticles with specific stoichiometry are prepared in a low-surface-tension liquid medium based on a coprecipitation reaction and in situ dispersed in the medium to obtain a suspension. Second, the suspension is in situ transformed into ultrafine oxide particles () by heat treatment where each nanoparticle reacts on a nanometre scale (nanometre reaction) with the least possibility of contact and agglomeration. The new method has brought about a new process termed an in situ nanometre reaction process (INRP). The new process can be used to manufacture finer BiPbSrCaCuO particles with a lower carbon content in a shorter time than the traditional coprecipitation process (TCP) because the agglomeration processes from filtration through drying to calcination are omitted.

In situ observation of phase changes by X-ray diffraction in the Bi-Sr-Ca-Cu-O system

An X-ray powder diffractometer has been equipped with a position-sensitive proportional counter and an optical microscope. This apparatus makes possible in situ microscopy and X-ray observation of the phase transition and phase relations affecting the crystal growth of homologous bismuth-based superconductors. A region of Sr-Ca-Cu-O oxide and liquid is found to exist above the decomposition temperature of Bi2(Sr,Ca)2CuOx, which is formed by the decomposition reaction of Bi2Sr2CaCu2Ox. The stable region of Bi2(Sr,Ca)2CuOx is extremely narrow at 3–7°C. The amount of liquid phase is estimated semi-quantitatively from visualized images through the optical microscope.

Testing of a prototype high temperature superconducting current lead

A prototype helium vapor-cooled current lead employing a ceramic high temperature superconductor was designed and tested. The lead which has a nominal current rating of 1 kA consists of copper and a ceramic superconductor sections and was designed for operation in 300 K/4.2 K temperature range. A single monolithic bismuth-based superconductor (BSCCO-2212) was used in the superconductor section. Extensive testing of the current lead was carried out to determine its performance such as steady-state boil-off rates at various operating currents, transient characteristics of the lead under zero-flow condition, and the effects of repetitive current cycling. At 1000 A operating current, the lead was found to require a steady-state helium vapor cooling flow rate equivalent to a liquid helium boil-off rate of 0.98 l/hr, an over 40% reduction from the conventional all copper lead. Cut-off of helium vapor flow for 230 seconds poses no overheating problem and no performance degradation was observed after 1000 cycles of repetitive current cycling between 0 and 1000 A. A very low contact joint resistance, 17 n/spl Omega/ for carrying 1000 A, was also observed at the 4.2 K lead terminal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Corrosion process of bismuth-based superconductor cuprates in a moisture atmosphere

Abstract Sintered pellets and single crystals of Bi 2 Sr 2 CaCu 2 O 8 (2212) and Bi 2 Sr 2 CuO 6 (2201) have been exposed to moistened air or just to water vapour. The following alterations observed have been studied by SEM, microanalysis, optical microscopic techniques, and FTIR. A possible reaction path for the alteration process is proposed. By means of optical and SEM observations, several morphologies of the alteration products have been observed. Two main steps, responsible for the degradation, have been found: the leaching of Sr and Ca cations from the matrix by fixed water, then a carbonate and hydroxide precipitation. In both cases, Ca and Sr extraction leads to Bi 2 CuO 4 .