Bi Sr Ca Research Articles

Observation of the flux line lattice and crystal defects in Bi–Sr–Ca–Cu–O single crystals

Abstract We have observed flux line lattice (FLL) structure in two different types of Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) single crystals with different pinning by using a Bitter decoration technique. We have also observed the microstructure and analyzed local chemical composition with wave dispersive spectroscopic analyses. In a low J c sample, we found two types of line defects, one with Ca-rich and the other with Ca-deficient. These defects extended almost parallel to the growth direction, which caused a distortion in the FLL structure. In contrast, no such defects were observed in the matrix in a high- J c sample, and a relatively ordered FLL was observed.

Levitation forces of bulk superconductors in varying fields

We measured the magnetic field distribution and the levitation force as bulk Y–Ba–Cu–O superconductor was moved in a vertical direction in the magnetic field generated from a Bi–Sr–Ca–Cu–O superconducting magnet. The levitation forces increased by stacking sliced bulk superconductor plates of the same thickness. The field in between two sliced plates was constant during the field varying process, showing that no field could penetrate into the interior of a bulk superconductor. Thus during the levitation, field distribution was altered at the surface thin layer of bulk superconductors.

Growth mechanism of Bi2212 whisker from bulk precursor

Abstract The Bi2212 whisker growth from the silver-added bulk precursor was compared with those from aluminum-added precursor. Especially, microstructural observation and analysis were performed near the surface of the bulk precursors around the root of the whisker using a scanning electron microscope with an electron probe microanalyzer. From the aluminum-added bulk precursor, Bi2212 + Ca–Cu–O + Al 2 O 3 , Bi2212 + Bi–Sr–Ca–Al–O + Al 2 O 3 , and Bi2212 + Bi–Sr–Ca–Al–O were observed, suggesting that its growth mechanism is the same as that from aluminum-added glass plate. Bi2212 whiskers grew from not only an Al-added bulk precursor but an Ag-added bulk precursor. Near the Ag-added precursor surface, Bi2212 + CuO, Bi2212 + Ca–Cu–O, and Bi2212 + CuO + Ag regions were observed. Ag was extremely segregated just below the surface. A microcrucible in the Ag-added precursor may be Ag or CuO.

High- Tc phase obtained in the Pb/Sb doped Bi–Sr–Ca–Cu–O system

Partial replacement of Bi by Pb and Sb produces materials of high- T c pure phase, with antimony playing an important role in accelerating the formation of the phase with the higher superconductive transition in the Bi–Sr–Ca–Cu–O system. The influence of the antimony precursors on the superconducting phases mechanism formation was examined. Using a solid state reaction route, two nominal compositions Bi 1.6Pb 0.3Sb 0.1Sr 2Ca 2Cu 3Oy and Bi 1.6Pb 0.4Sb 0.1Sr 2Ca 2Cu 4Oy were investigated. The sources of antimony were Sb 2O 3, αSb 2O 4 and a prepared mixture Bi 1.9Sb 0.1O x . The mechanism formation of the phases upon annealing was investigated using X-ray diffraction and simultaneous thermal analysis. Electrical properties of the obtained materials were evaluated. The presence of the antimony ions determined a higher reactivity of the system as well as the promotion of the superconducting high- T c phase enhancement.

Revision of the thermodynamic descriptions of the Cu–O, Ag–O, Ag–Cu–O, Bi–Sr–O, Bi–Ca–O, Bi–Cu–O, Sr–Cu–O, Ca–Cu–O and Sr–Ca–Cu–O systems

We have revised the thermodynamic descriptions of several subsystems of the Ag–Bi–Sr–Ca–Cu–O system. In the Cu–O system the description of the liquid phase was changed to remove an inverted miscibility gap at high temperature and to get a better fit of the CuO liquidus. Also the dissolution model for O in fcc-Cu and fcc-Ag was changed from substitutional to interstitial. The liquid phase description in the Ag–Cu–O, Bi–Cu–O and Ca–Cu–O systems was adjusted to accommodate for the changes in the Cu–O system. The Bi–Sr–O and Bi–Ca–O systems were completely reoptimised to include new extensive thermodynamic data. The Sr–Cu–O system was also completely reoptimised based on a revaluation of existing thermodynamic data, triggered by new data on melting temperatures at low oxygen partial pressures. The Sr–Ca–Cu–O system was completely reoptimised in order to be able to describe melting relations at the Bi 2Sr 2CaCu 2O z composition reasonably.

BCS-like Bogoliubov quasiparticles in high-T(c) superconductors observed by angle-resolved photoemission spectroscopy.

We performed high-resolution angle-resolved photoemission spectroscopy on triple-layered high-T(c) cuprate Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta). We have observed the full energy dispersion (electron and hole branches) of Bogoliubov quasiparticles and determined the coherence factors above and below E(F) as a function of momentum from the spectral intensity as well as from the energy dispersion based on BCS theory. The good quantitative agreement between the experiment and the theoretical prediction suggests the basic validity of BCS formalism in describing the superconducting state of cuprates.

Effects of conductor anisotropy on the design of Bi–Sr–Ca–Cu–O sections of 25 T solenoids

The development of a 25 T superconducting magnet is usually envisioned with the use of an innermost coil wound with high-temperature superconductor (HTS) material. At present, Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox (BSCCO) conductors are the only candidate conductors available with sufficient length and current carrying capability. Unlike NbTi and Nb3Sn conductors, the BSCCO crystal structure and thus properties are strongly anisotropic. In conductor form, various degrees of anisotropy occur. It is often assumed that this anisotropy simply implies that radial field components must be minimized. We show that this assumption can be misleading. Using the average grain colony misalignment angle to parameterize the anisotropy, three regimes are distinguished in the relationship between average grain colony misalignment and critical current limiting field components. The implications of these separate regimes on the design process for 25 T superconducting magnet design are discussed.

Trapping control of phase development in zone melting of Bi–Sr–Ca–Cu–O superconducting fibres

Highly-texturized polycrystalline fibres of the Bi–Sr–Ca–Cu–O system have been grown by the laser floating zone technique at seven different pulling rates: (1.1, 2.2, 4.17, 8.3, 16.7, 33.3, 60.5) × 10−6 m s−1. The assessment of the cation segregation at the solid/liquid interface allowed us to calculate their equilibrium and effective distribution coefficients. The equilibrium distribution coefficients (k0,Bi = 0.55, k0,Sr = 0.97, k0,Ca = 1.67, k0,Cu = 1.10) were estimated using the Burton, Primm and Slichter (BPS) theory by taking into account the determined effective values. The effective distribution coefficients tend to unity as long as the pulling rate increases. The composition profiles along the initial transient region of the solidified fibres show a fast approach to the nominal composition as the pulling rate increases. The outstanding effect of the growth speed on superconducting phase type development is explained based on the solute trapping phenomena. The sequence of crystallization for superconducting phases (‘2212’ → ‘4413’ → ‘2201’) with pulling rate is a spontaneous effect of the system thermodynamics in order to balance the Bi trapping. This phase sequence corresponds to the smallest change of Bi chemical potential from the liquid phase to the solid phase. A diagram of free energy curves of the interdendritic superconducting phases illustrates the partitionless solidification phenomena at the highest growth speed.

Thermal degradation of Y–Ba–Cu and Bi–Sr–Ca–Cu precursors for the preparation of high temperature superconductors

This paper presents the results of thermal analysis (TA) with simultaneous mass spectroscopy and FTIR investigations of Y–Ba–Cu-polymer and Bi–Sr–Ca–Cu-polymer precursors where the polymers are either novolak or poly(acrylic acid) (PAA). It is shown that the thermal degradation behaviour of precursors influences the quality of high temperature superconductor (HTSC) films, which were characterized by electrical measurements for determination of transition temperature and critical current density.

Composition, Microstructure, and Superconducting and Ferroelectric Properties of Bi–Sr–Ca–Cu–O/Pb–Ti–Zr–O Heterostructures

Ferroelectric–superconductor heterostructures consisting of a ferroelectric Pb–Ti–Zr–O film on a superconducting Bi–Sr–Ca–Cu–O ceramic substrate or a superconducting Bi–Sr–Ca–Cu–O film on a ferroelectric Pb–Ti–Zr–O ceramic substrate with Ag, Au, Pd, and Pt barrier layers are prepared and investigated. Thin-film Bi2Sr2CaCu2O8 + x /ZrO2/Pb(Ti0.6Zr0.4)O3 (superconductor/barrier/ferroelectric) heterostructures on LaAlO3 substrates are for the first time produced and characterized. The superconducting and ferroelectric transition temperatures in the heterostructures are 80 and 638 K, respectively.

Anisotropic superconducting properties and fabrication of submicrometre bridges in misaligned Bi–Sr–Ca–Cu–O (2212) films

In this paper, we report on misaligned Bi–Sr–Ca–Cu–O (2212) films that have been deposited on vicinal strontium titanate substrates using a dc sputtering system. We measured the temperature dependences of resistivity across and along the terrace, and only the resistivity across the terrace slightly decreased with the increase of the temperature in the normal state region. The estimated anisotropy parameter γ was smaller than that of single crystal, but a significant anisotropy was observed. Submicrometre bridges were fabricated, and the temperature dependence of the critical current density was investigated. The value of the critical current density across the terrace is smaller than the value of that along the terrace. This suggests that the current partially flows along the c-axis. However, a multi-branch structure was not observed even after post annealing in oxygen atmosphere at low pressure.

Measurements of magnetic fields of levitated bulk superconductors

We have measured the magnetic field and the levitation force of bulk Y–Ba–Cu–O superconductors as a function of their levitation height which was controlled by the magnetic field generated from the Bi–Sr–Ca–Cu–O superconducting magnet. The height dependence of the levitation force could well be explained in terms of the field gradient in the sample and radial component of magnetic field. Comparative study of three bulk samples with different dimensions showed that the diameter was more important than the thickness for the enhancement of the levitation force.

ChemInform Abstract: LnSrAlO4 (Ln: Nd and La): A New Type of Perovskite Ceramic Substrate for Bi—Sr—Ca—Cu—O Superconducting Thick Films.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Growth, contacting and ageing of superconducting Bi-2212 whiskers

We report the growth of highly oriented microscopic whisker-like crystals in the Bi–Sr–Ca–Cu–O system by means of glassy precursors. The dependence of the growth on the stoichiometric composition and on the temperature and duration of the annealing process has been studied. Chemical impurities have been investigated from the point of view of the morphology, the elemental composition and the crystal structure, identifying the presence of CuAl2O4, Sr1.2Bi0.8O3 and Al. Electrical contacts have been fabricated by means of thermal evaporation and diffusion. Their sizes have been carefully measured, achieving contact resistivity in the range of 0.2–3.7 × 10−6 Ω cm2. A very slow degrading of the contacts and the crystals on a time scale of a few years has been detected. This is associated with a decrease in Tc, which is probably due to oxygen release from the material.

Low energy excitation and scaling in Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4) (n=1-3): angle-resolved photoemission spectroscopy.

Angle-resolved photoemission spectroscopy (ARPES) has been performed on the single- to triple-layered Bi-family high-T (c) superconductors (Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4), n=1-3). We found a sharp coherent peak as well as a pseudogap at the Fermi level in the triple-layered compound. Comparison among three compounds has revealed a universal rule that the characteristic energies of superconducting and pseudogap behaviors are scaled with the maximum T (c).

The effects of crystallization on the magnetic properties and critical current in Bi–Sr–Ca–Cu–O glass–ceramics

We report on the influence of crystallization on the dc magnetization, the ac susceptibility, and the intergranular and intragranular critical current density of Bi4Sr3Ca3Cu4Ox crystallized glass. The samples, characterized by x-ray diffraction, contained mainly a Bi2Sr2Ca1Cu2O8 superconducting phase. The transition to the superconducting state was investigated by magnetic methods: dc magnetization and ac susceptibility. All the samples exhibited diamagnetic properties below 80 K, which is in agreement with the critical temperature of the Bi2Sr2Ca1Cu2O8 phase. The superconducting volume fraction and the values of critical current were evaluated from the magnetization measurements of the samples cooled in an applied magnetic field and the measurements of magnetization hysteresis. The values of critical current for all the samples were quite small, in the range of 50–100 A cm−2 for intergranular current, depending on the amount of superconducting phase in the sample.

Growth and electrical transport characteristics of Bi 2Sr 2Ca 1Cu 2O x and Bi 2Sr 2CuO x single-crystal whiskers using tellurium-doped precursors

Bi 2Sr 2CaCu 2O x (Bi2212) and Bi 2Sr 2CuO x (Bi2201) single-crystal whiskers were grown by annealing sintered Te-doped Bi–Sr–Ca–Cu–O precursors. The growth of Bi2212 or Bi2201 whiskers definitely depends on the Ca content of precursors; the optimal composition is Ca-rich Bi 2Sr 2Ca 2Cu 2Te 0.50O x for Bi2212 and Bi 2Sr 2CaCuTe 0.50O x for Bi2201. In the precursors Te ions exist in the phase of (SrCa) 3TeO 6. The whiskers contain no Te element. The Bi2212 whiskers have a critical temperature of about 80 K and the critical current with a multibranched structure of the current–voltage characteristics due to the intrinsic Josephson junctions along the c-axis is quite uniform, showing that the whiskers are homogeneous and of good quality. The Bi2201 whiskers show semiconducting resistance with no superconducting transition down to 4.2 K.

Electronic structure of the trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta).

The low-energy electronic structure of the nearly optimally doped trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface and the superconducting d-wave gap and coherence peak are observed and compared with those of single- and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with T(c) for various optimally doped materials.

RESrAlO 4 (RE=Nd and La): a new type of perovskite ceramic substrate for Bi–Sr–Ca–Cu–O superconducting thick films

A suitable new type of substrate RESrAlO 4 (RE=Nd and La) for making Bi2212 thick films has been synthesized by solid state reaction. X-ray diffraction indicated that both compounds are single phase when synthesized at 1350–1500°C. The compounds are both of tetragonal structure and have high melting points together with low dielectric constants and energy loss. They are chemically compatible with Bi2212. Strongly c-axis oriented Bi2212 thick films with a T co of 85 K were successfully grown on the polycrystalline substrates. RESrAlO 4 is suitable for use as a substrate material for growing Bi–Sr–Ca–Cu–O (BSCCO) thick films for microwave devices.

Studies on Photoinduced Effects in Ag/Bi-Sr-Ca-CuO Heterojunctions

Polycrystalline films of Bi–Sr–Ca–CuO are deposited on silver substrate using the pulse electrodeposition technique and then electrochemically oxidized at room temperature in 1N KOH solution. Films thus prepared show a resistanceless state below 103 K. Photoinduced effects in heterostructures formed with Bi-based superconducting thin films and Ag (Ag/BSCCO) are studied and reported for the first time. Photovoltages generated across the junction with visible light excitation are found to vary with level of excitation and temperature. The magnitude of the photovoltage is found to decrease linearly with decrease in temperature and dropped down suddenly at 104 K, the superconducting transition temperature of BSCCO present in the junction.