Doped Bi Sr Ca Research Articles

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.

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.

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.

Mechanical processing of highjcbscco superconductors

Abstract High J c superconducting oxides can be obtained by processing polycrystalline powders to achieve high degrees of densification and sharp crystallographic textures characterized by the conducting crystallographic planes lying parallel to the direction of the current flow (i.e., in the plane of a conducting tape or parallel to the axis of a wire). In the present study, we investigate the densification and texture evolution in a Pb doped Bi—Sr—Ca—Cu oxide (BSCCO) under axisymmetric and plane strain (channel die) compression. Experimental measurements of the microstructural evolution, including crystallographic texture and grain morphology, are presented as a function of the degree of deformation and densification. The orientations of the conducting planes (c planes) are shown by measured X-ray pole figures and analyses of these orientations are given for both tests. A model based on crystal plasticity theory is proposed to simulate the inelastic deformation and texturing of the BSCCO oxide. Predicte...

Elastic and plastic behavior of lead and silver doped BiSrCaCuO superconductors

Bi 1.7Pb 0.3Ag x Sr 2Ca 2Cu 3O y ( x = 0.0, 0.1, 0.2, 0.3 and 0.4) superconducting samples have been synthesized by the matrix method. From X-ray diffraction and d.c. electrical resistivity results, it has been confirmed that silver doping does not poison the superconductivity and T c (0) varied between 95 K and 105 K. The ultrasonic compressional ( V 1 ) and shear ( V S ) velocities at room temperature were determined for all the samples by the ultrasonic pulse transmission technique. The Young's modulus and rigidity modulus values were calculated and were found to decrease with increasing silver doping. Microhardness measurements were performed using the indentation method. The hardness decreased with increase in lead concentration and further decreased with addition of silver. The hardness values were calculated for all the samples from the elastic data and these values are in good agreement with the experimental data.

Elasticity study on lattice instability in BiSrCaCuO

The frequency dependences of heights and positions of the attenuation peaks at 95K and 250K for Bi 2Sr 2CaCu 2O 8 single crystal (T c=84K) show the characters of phase transitions. The pseudo-static ferroelastic σ-ϵ loops of Pb doped BiSrCaCuO polycrystal (T c=107K) always appear around 130K and 250K. The energy loss (loop area) is independent of the strain rate and increases with the strain amplitude, which also exhibits the characteristics of static hysteresis loss related to phase transitions instead of the Debye relaxation mechanism. Some discrepancies in elasticity measurements so far observed for high Tc superconductors have been analyzed.

A NEW PHASE IN Pb AND Sb DOPED Bi–Sr–Ca–Cu–O SYSTEM

In this paper, a new phase in the Pb and Sb doped Bi–Sr–Ca–Cu–O system with T c about 140 K is identified by electron diffraction. The transition temperature is determined by the susceptibility measurement. There may exist some connections between the new phase and the 110 K phase. The connections are considered to be the key to the improvement of T c .

Preparation and properties of superconducting (T c = 114 K) Pbdoped BiSrCaCu oxide

Nominal substitution of Pb for Bi in ceramic BiSrCaCu oxide leads to a phase with a superconducting transition at T c= 114 K. This new phase has lattice parameters a ≈ b= 0.54 nm, c= 3.78 nm and a structural modulation with wave vector parallel to the [010] direction (q −1= 4.7 nm). Defect free zones of this phase are larger, i.e. a few hundred nanometers, than in undoped Bi 2Sr 2Ca 2Cu 3O 10+δ. Preliminary results about electrical properties, chemical composition and structure of this new phase are presented.