Bi Sr Ca Research Articles

Thermodynamic stabilities of ternary oxides in BiCuO system by solid electrolyte EMF method

There are four high T c compounds in the BiSrCaCuO system, the thermodynamic characterization of which may require precise Gibbs energy data on ternary compounds in different subsystems. Hence, phase equilibrium studies have been carried out on the less known Bi 2O 3Cu 2OCuO system and a partial isothermal phase diagram has been determined at 973 K. Based on these equilibrium studies, three galvanic cells based on stabilized zirconia as the electrolyte and one galvanic cell based on single crystal CaF 2 as the electrolyte have been studied in the temperature range 650–950 K. From the EMF results, the following least-squares expressions for the standard Gibbs energy of formation of ternary oxides, ΔG f, ox o , from their constituent binary oxides have been derived. ▪ The expressions for log PP o2 and log a CuO over the relevant mixture of phases have also been derived and reported.

Growth of high quality BiSrCaCuO single crystals by the self-flux method with a temperature-holding process

We prepared the BiSrCaCuO(Bi-based) single crystals by the self-flux method with a temperature-holding process. The plate-like Bi-based single crystals with the size of about 2 x 2mm 2 were prepared at the holding temperature of 840°C. From the X-ray diffraction patterns, we found that the c-axis unit cell length of the crystal ( C 0=39 A ̊ ) was longer than that of an 80K phase Bi-based single crystal.

Effects of a various Pb-oxides doping on the superconductivity of BiSrCaCuO ceramics

The 110K-phase BiSrCaCuO (Bi-based) superconductors were prepared using a variety of Pb-oxides (PbO, PbO 2 and Pb 2O 3), and their superconducting properties were investigated. From the results, we found that the doping of Pb 2O 3 into Bi-based superconductors was effective in forming a 110K-phase. The XRD results showed that the volume fraction of a 110K-phase in the prepared samples increased by doping Pb 2O 3.

Evaluation of the degree of texturing and relative phase content in hot-pressed Bi(Pb)SrCaCuO superconductors

Peak intensities from (001) planes of the 2223 phase was measured to receive information on the c-axis orientation, while the ratio of (0 0 10) and (0 0 14) peaks intensities of the high- T c 2223 phase to the (0 0 8) and (0 0 12) peaks of the low- T c phase gave information on the relative content of the high- T c phase. Sintering prior to hot press3ng has shown strong effect on the resulting structure and physical properties with the optimum for 26MPa and 850°C between 96h and 120h. the highest value of J c for the uniaxially hot pressed pellet was ∼11,500Acm −2 at 77K and OT.

Formation of sub-micron SrZrO 3 particles in Bi 2Sr 2CaCu 2O 8+x superconductor

Composite superconducting materials of the BiSrCaCuO (2212) system with fine precipitates of SrZrO 3 have been prepared from co-precipitated oxalates using melt including procedures in air and in oxygen. SrZrO 3 phase formation and microstructure of the materials at different steps of processing, as well as magnetic properties of the superconductors prepared have been studied.

Oriented Bulk Consolidation of Bi–Sr–Ca–Cu–O by Shock-Loading Method

Shock compaction experiments were carried out for Bi2Sr2CaCu2Oy particles sorted to 46–74 µ m and packing density of 50–82% at a shock pressure of 8 GPa. Bulk density reached 95% by shock compaction independent of the porosity. The most effective orientation was achieved by shock loading for the packing density of 67% and with post annealing at 870°C. The texture of the shocked plus postannealed specimen showed crystal growth not only within the c-plane but also along the c-axis. The Meissner volume fraction of the shock compacted specimen decreased with decreasing packing density but the onset temperature did not change. The magnetic torque of shock plus annealed specimen showed the alignment of particles.

Microstructure of BiSrCaCuO thin films on YAG substrate

We have succeeded in fabricating the superconducting BiSrCaCuO thin films on Y 3Al 5O 12(YAG) single crystal substrate, which had very smooth surface. The origin of the smooth film surface was examined by HREM observation of the microstructure. We proposed that the long-range lattice matching with the YAG substrate has a important role for fabricating the smooth surface film.

Cu 2p Photoelectron and 2p 3/2-Valence-Valence Auger Electron Spectra of Cuprate Superconductors

We have observed many-body effects in both the Cu 2p photoelectron and 2p3/2-valence-valence (L3VV) Auger electron spectra for thin films of Bi2Sr2Cax Cu1+x O6+2x (x=0, 1, 2), La2-x Srx CuO4 (x=0, 0.13), and ErBa2Cu3O7-x ,y (x<y). We reviewed the relationship between the many-body effects and high-T c superconductivity of cuprate superconductors. Enlargements of both intensity ratio and energy separation of the |cd10L> to |cd9> lines in the 2p spectra corresponded with an increase of the mixing of |d8L> and |d7> states in the L3VV spectra. Enlargement of the parameters of many-body effects resulted from an increase in covalency of the Cu–O bond. An enlargement of the transfer integral is required for realization of high-T c superconductivity of Bi–Sr–Ca–Cu–O and La–Sr–Cu–O systems. The 90 K superconductivity in Er–Ba–Cu–O and Y–Ba–Cu–O systems was realized by increasing the charge transfer energy.

Formation of high quality thin 2212-phase films from BiO 1.5SrOCaOCuO multilayers

Highly c-axes oriented 2212-phase films have been synthesized from the BiO 1.5CuO(SrO,CaO) multilayers and uniform magnetron sputtered amorphous BiSrCaCuO precursors using postannealing in air at (700÷850)°C. In situ high temperature XRD studies have been carried out to elucidate mechanisms and kinetics of the two-layer phase formation. High crystalline quality of the 2212-phase films formed from the multilayers we associate with accelerated two-layer phase growth in presence of fugitive liquid and intermediate Bi and Sr oxyde based solid solution [1].

Study of superconducting and physical properties of 110 K (Bi, Pb)SrCaCuO superconductors from glass precursor

High quality samples of 110 K(Bi 1.6Pb 0.4) Sr 1.7 Ca 2.3Cu 3 O y were prepared in the form of long-length rods by rapid quenching of the melt, which showed a glass transition temperature of 379.77°C, crystallization temperature of 463.4°C and melting temperature of 861.5°C. We also prepared glasses of Bi 1-xR xSrCaCuO y (R = Al and x = 0.5) system at various melting temperatures which on further heat treatment under appropriate conditions, crystallized into superconducting phase(s). It was found that copper ions in the glasses exists mainly in the Cu(I) ionic state and the Cu(I)/Cu(total) ratio increases with glass melting temperature. The control of the Cu(I)/Cu(total) ratio leads to the successful continuous drawing of BiCaSrCuO glass fibers.

Half-Unit Cell Growth of Bi–Sr–Ca–Cu–O Thin Films

The growth units of superconducting Bi–Sr–Ca–Cu–O thin films were examined. The films were prepared on Y3Al5O12 (YAG) single-crystal substrates by metalorganic chemical vapor deposition (MOCVD). The growth process of the films at the initial stage was investigated by cross-sectional high-resolution transmission electron microscopy (HREM) and atomic force microscopy (AFM). We found evidence of half-unit cell growth, and the top layer of the half-unit was determined to be a Bi–O layer by angular-resolved measurement using X-ray photoelectron spectroscopy (XPS).

Effect of additional elements in the glass precursor on the growth of the Bi2Sr2Ca2Cu2Ox whiskers

The effect of the doping on the growth and superconducting properties of whiskers in the Bi–Sr–Ca–Cu–X–O system (where X = Na, B, Ga, and Pb, respectively), prepared by heating a glassy melt-quenched plate in flowing oxygen, is reported. The thermal behavior of the glassy samples (studied by DTA, XRD, and SEM techniques) was found to be dependent on the dopant as well as on its concentration. The Bi2Sr2CaCu2Ox (2212 phase) whiskers were grown only from the Ga-doped system annealed at 855 °C. The dependence of the mechanism of the whiskers' growth on the dopant is also discussed.

Effects of oxygen partial pressure on the crystallization of amorphous Bi–Sr–Ca–Cu–O and Bi–Sr–Ca–Cu–O + Ag

The temperatures and pathways of crystallization for amorphous Bi–Sr–Ca–Cu–O are strongly dependent on oxygen partial pressure (Po2), the oxidation state of the glass, and the presence of Ag. Reducing the Po2 from 1 to 0 bar lowers the onset of melting 100 °C, but does not change the onset of crystallization. Decreasing Po2 does inhibit the formation of (CaSr)CuO3 (011). Although Ag appears to be immiscible in Bi–Sr–Ca–Cu–O, finely distributed Ag lowers the onset of melting by 20 to 35 °C, depending on Po2. In oxygen-deficient glass, two exotherms are observed upon heating. The first exotherm at 460 °C is independent of Po2, and Ag and corresponds with the formation of Bi2Sr2CuO6 (Bi-2201). The second exotherm occurs at 486 °C with Ag or 500 °C without Ag. The onset temperature of the second exotherm does not change with Po2, but the exotherm decreases in intensity with decreasing Po2. EXAFS indicates that in the as-quenched amorphous material, Cu is in a reduced state. Annealing the amorphous material in oxygen below the first exotherm (i.e., glass relaxation) increases the oxidation state of the Cu to that necessary for the formation of the Bi2Sr2CaCu2O8 (Bi-2212) without additional oxygen diffusion. This relaxation of the glass increases the crystallization temperature of the Bi-2201 to 500 °C. The crystallization sequence of Bi-2201 to Bi-2212 occurs at all Po2 ≥ 0.1 bar, but the composition of the secondary phases changes in the unrelaxed glass. Relaxing the glass eliminates liquid formation at low temperatures, allowing for rapid formation of the Bi-2212 phase with minimal formation of secondary phases for 0.1 ⋚ Po2 ⋚ 0.2 bar.

Formation of Bi-2212 superconducting whiskers from melt-quenched BSCCO containing alumina

Bi–Sr–Ca–Cu–O (BSCCO) superconducting whiskers (2212 phase) were prepared by heating in air the compacted specimens of the mixtures of melt-quenched Bi2SryCa2Cu4Al1Ox powders and alumina powders. Formation of the whiskers depends on the composition and the applied pressure of the compacts. The optimum composition of the melt-quenched products for preparing the long whiskers is Bi2Sr2Ca2Cu4Al1Ox. Superconducting whiskers &lt;1 mm in length (2212 phase) containing an excess amount of copper were grown numerously from the specimen compacted at 20 MPa; long whiskers (2212 phase) of 1–5 mm in length were obtained from that compacted at 180 MPa. These whiskers showed diamagnetic signals below Tc ≃ 80 K.

Statistical mechanics of flux lines in oxide superconductors

The structure of the unpinned vortex liquid in strongly anisotropic layered high- T c oxide superconductors in a magnetic field B perpendicular to the layer plane is investigated by using appropriate classical liquid-state theories. The direct correlation function so obtained is used as input for a parameter-free, first-principles calculation of the liquid-to-Abrikosov-lattice transition boundary T f( B) within the framework of the density functional formalism. This transition boundary is found to have a shape and location similar to that observed in experiments on strongly anisotropic materials, e.g. BiSrCaCuO. The effects of random pinning disorder on the equilibrium density correlations of the vortex liquid and its freezing transition are investigated by combining the methods mentioned above with the replica formalism.

Structural characterization and properties of superconducting thin films produced by pulsed laser deposition

This work deals with the production and characterization of superconducting BiSrCaCuO thin films realized by using the pulsed laser deposition technique. The effect of annealing parameters on the structure and quality of the as-deposited and annealed thin films of BiSrCaCuO are reported and discussed, as well as of the sintered pellets used as targets. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction have been utilized to characterize both the sintered pellets and the thin film.

A Model Analysis of the Thermal Conductivity of Ag-doped Bi–Sr–Ca–Cu–O Superconducting Oxide

A phenomenological model to analyze the transport phenomena in inhomogeneous materials is proposed and applied to the measured thermal conductivity of Ag-doped Bi–Sr–Ca–Cu–O (Bi2212) superconducting oxide. Based on the model, the effective ratios of the doped Ag amount in the grain boundary to that inside of the grain are determined to be 0.75:1.0 for a Bi2212+15 wt%Ag specimen and 0.85:1.0 for a Bi2212+10 wt%Ag specimen. The model analyses indicate that doped Ag particles preferentially occupy the grain boundaries, contributing to the formation of the linked Ag heat path in the oxides.

High-temperature deformation and fracture of Bi–Sr–Ca–Cu–O superconductors

Dense polycrystalline Bi2Sr2Cu2Ox (2201), Bi2Sr2CaCu2Ox (2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (2223) specimens were compressed in air at 730–835 °C. All of the materials exhibited an apparent steady-state creep response. Strain rate was proportional to stress to the 3.1–3.8 power. Apparent activation energies for the deformation processes were 520 ± 50 kJ/mole for the 2201, 630 ± 210 kJ/mole for the 2212, and 960 ± 210 kJ/mole for the 2223. Transmission electron microscopy revealed substantial generation and propagation of basal-plane dislocations during deformation. Few nonbasal-plane dislocations were observed. Intergranular fracture was evident in all deformed samples, and intragianular fracture was evident along the basal planes of some grains. It is suggested that the kinetics of fracture were determined by dislocation motion within the grains.

Relation of starting precursors to the resulting high-Tc phases in the Pb and Sb doped Bi—Sr—Ca—Cu—O system

The introduction of more reactive precursors for Pb and Sr (oxalates), as well as Ca (citrate) and the use of a Bi nitrate decomposition route, has increased the percentage of the high-Tc (2223) phase in the Bi—Sr—Ca—Cu—O (BSCCO) system. Partial substitution of Bi(Pb) with Sb gives an almost single (2223) phase sample. In addition, a single (2212) phase sample is obtained when high purity Bi2O3 is used as a precursor, whereas Bi acetate leads to semiconducting behavior. The morphology of the samples is studied with a scanning electron microscope (SEM), the stoichiometry with energy-dispersive x-ray analysis (EDAX), and the structure with x-ray diffraction (XRD), while the superconducting properties are investigated by dc-resistivity, ac-susceptibility, and SQUID magnetometry techniques.

Thermodynamic fluctuation in doped BiSrCaCuO superconductors with 110K phase

The resistivity has been carefully measured for four sintered samples of Pb and Pb/Sb doped BiSrCaCuO superconductors with the 110 K phase from zero resistance temperature up to 300 K. The thermodynamical fluctuation have been fitted on the form Δσ∝ε x ( ε=( T− T c )/ T c ) in the regions -4 < ln ε < -2. By choosing T c in different ways, it is shown that consistent results only could be obtained when T c is defined according to the Lawrence-Doniach theory.