Compositional range of the Bi2Sr2CaCu2OxHTc-superconductor and its surrounding phases (original) (raw)
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Physica C: Superconductivity, 1992
The phase relationships and solid-solution region of the Bi2Sr2CatCu2Oy (2212) superconductor were investigated for compositions around the ideal 2212 stoichiometry at 8650C in one bar of oxygen. Changes in the starting composition were accommodated by changes in the types and composition of the secondary phases present, the number ofintergrowths within the 2212 phase, and the solid solution composition of the 2212 phase. Compositional analysis of the superconducting phase was carried out in the transmission electron microscope (TEM) in order to separate the effects of solid-solution changes and the presence of intergrowths upon measured compositions. The actual solid-solution region determined from TEM measurements showed most of the solid solution substitution to occur between Sr and Ca. The highest superconducting transition temperatures (To) were found in annealed samples for which the measured Sr+Ca content of the 2212 phase was closest to the ideal stoichiometric ratio of 3 (42.86 at.%). No correlation was found between the transition temperature and lattice parameters of the superconducting phase. 0921-4534/92/$05.00
The extent of the single phase fields of boLh superconductors, Bi 2 Sr 2 CaCu 2 0 8 • 0 , "2212", and Bi 2 .,Sr 2 _.Cu0 0 • 6 , "11905", at 830°C in air were determined. The extension of the "2212" solid solution wi thin the compositional tetrahedron is a trigonal bipyramid with a length of 13.7 mo!% parallel lo the SrO-CaO edge, and 9 mol% perpendicular lo it. This phase only exists in the quaternary system. The tolerance of the phase Lo CuO variation is smaller than ±1.2 mo!%. The single phase field of the "11905" phase extends into the tetrahedron. The Ca
Single-phase region of the 2212-BiSrCaCuO superconductor
Physica C: Superconductivity, 1993
The phase relationships and solid-solution region of the Bi2Sr2CaCu208+6 (22 12 ) superconductor were investigated at 850°C under air atmosphere in a cross-section of the system Bi-Sr-Ca-Cu-(0) defined by the formula Bi2+,SrS_y_xCaxCu10s+6. The system was studied by means of XRD and EMA and an approximate position of the 22 12 single-phase region is delimited by the values of y=O.l and 0.8SxS 1.3. The single-phase region determined may be divided into two subregions, %-rich in the range 0.8 SxS 1 .O and Ca-rich in the range 1.1 SX< 1.3, these differing in the number and character of intergrowths. The highest superconducting transition temperature (r,) was found for x=0.8.
Bulletin of Materials Science, 1991
Single crystals of Bi2Sr2CaCu2Os (2212) have been grown by self-flux technique using stoichiometric and non-stoichiometric melts of excess CuO and Bi20 3. Single-crystal and powder X-ray diffraction studies have been made on the grown crystals to confirm their single crystallinity and structure respectively. Resistivity and susceptibility measurements provide information on the superconducting nature of the crystals. The effects of fluxing agents and starting composition on surface morphology and superconductin~ properties have been discussed.
Superconductivity up to 110 K in Bi2Sr2Ca2Cu3O10 compounds
Revue de Physique Appliquée, 1989
2014 Nous avons étudié dans le système Bi-Si-Ca-Cu-O le composé responsable de la supraconductivité jusqu'à 110 K, de formule idéale Bi2Sr2Ca2Cu3O10. Les mesures d'aimantation montrent la présence de deux phases dans les échantillons, avec des transitions à 80 K et 110 K. En faisant varier la composition et les traitements thermiques de ces échantillons, nous avons réussi à augmenter la proportion de la phase supraconductrice jusqu'à 110 K. L'effet Meissner atteint 30 % de -3/8 03C0 à 90 K pour les échantillons non dopés et 50 % pour ceux dopés au plomb. La grande réversibilité des courbes d'aimantation en fonction du champ au voisinage de Tc nous a permis d'évaluer le champ critique thermodynamique. Celui-ci conduit à un coefficient de chaleur spécifique électronique similaire à celui des composés YBaCuO. Abstract. 2014 In the Bi-Sr-Ca-Cu-O system, we have studied the compound with the ideal formula Bi2Sr2Ca2Cu3O10, responsible for the superconductivity up to 110 K. The magnetic measurements reveal the presence of two phases in the samples with superconducting transitions up to 80 K and 110 K. By varying the composition and the thermal treatment of those samples, we have succeeded in increasing the amount of the superconducting phase with Tc up to 110 K. The Meissner effect reaches 30 % of -3/8 03C0 at 90 K for the undoped samples and more than 50 % for the samples doped with Pb. Because of the high reversibility of the magnetization versus magnetic field around Tc, we have evaluated the critical thermodynamic field. This one gives an electronic specific heat coefficient similar to the one of YBaCuO compounds. Revue Phys. Appl. 24 (1989) 485-488 MAI 1989, Classification Physics Abstracts 74.70 Introduction.
Physica C: Superconductivity, 1988
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1998
Local structure of CuO 2 plane of the superconducting Bi 2 Sr 2 CaCu 2 O 8ϩ␦ ͑Bi2212͒ crystal at the optimum doping has been investigated by in-plane polarized Cu K-edge x-ray-absorption spectroscopy. We have determined the quadrupole character of the 1s→3d x 2 Ϫy 2 transition in the x-ray-absorption near-edge spectra by rotation of the in-plane polarization geometry by 45°from the Cu-O-Cu direction. The nonzero intensity of this transition in the polarization vector parallel to the Cu-O-Cu direction indicates local structural distortion of the CuO 4 square plane. The statistical distribution of the instantaneous Cu-O bonds is determined by polarized extended x-ray-absorption fine structure and discussed. ͓S0163-1829͑98͒05037-1͔
The confirmation of superconductivity in the Bi_Sr_Ca_Cu_O system
Solid State Communications, 1988
By exploring more than 30 compositions in a quaternary oxide system BiSrCaCuO, we have (1) confirmed the existance of superconductivity up to 114K and (2) located the composition range for the superconducting phase. Several compositions in the proximity of the BiSrCaCu compositions 6:5:3:6 and 2:2:1:2 revealed identical diffraction patterns, indicating a broad homogeneity range for the superconducting phase. The equilibrium phase exhibits a TC ∼ 86K. Depending upon the heat treatment conditions, multiple superconducting transitions at temperatures above and below 86K have been observed.
Physica C: Superconductivity, 1997
conductor with high current ability is believed to possess a certain microstructure with good junctions between grains, high texture, and a fine distribution of second phases and crystal defects in the superconductor matrix [1,2]. The defect structure is essential for flux pinning enhancement, which is in particular the most important problem for Bi-containing HTSC [3,4]. Elaboration of processing conditions allowed to obtain superconducting Bi-2212 tapes with critical current densities above lo5 A/cm2 at 4.2 K and lo4
Journal of Physics: Condensed Matter, 1989
We have made four-probe conductivity, AC susceptibility and x-ray diffraction measurements on the following compounds: nine compositions of BiCa,-,Sr,Cu,O, with 0.1 s x < 1, four samples of BiCaSrCuzOz with variations in the ambient and in heat treatment, and the samples with the starting compositions BiCal zjSro 7jCuzOp, Bi,CaSrCu20, and Bi2Caz,,,Sro 7sCuz0,. Many of these Bi-containing compounds exhibit superconductivity around 80 K. Sharp drops in resistivity near 120 K have also been observed in a few cases. The dependence of T, on starting stoichiometry, synthesis conditions and structural parameters are discussed.