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1.
The stability of the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound has been evaluated under conditions of elevated temperature (500°-860°C) and elevated oxygen fugacity (i.e., in O2 /Ar gas mixtures containing ≤120% O2 , at total pressures of 5207 MPa). At sufficiently high oxygen fugacities and temperatures, the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound transformed into a mixture of a strontium-rich (Bi,Pb)1 -(Sr,Ca,Cu)2 Oy -type compound, a calcium-rich (Bi,Pb)2 -(Sr,Ca,Cu)2 Oy -type compound, CuO, and a small amount of (Sr,Ca)O. The decomposition of the (Bi,Pb)2 Sr2 Ca2 -Cu3 O10±δ -type compound was accompanied by a 2%-3% weight gain, which was consistent with an oxidation reaction. The conditions of oxygen fugacity and temperature leading to decomposition, and the resulting decomposition products, are compared for the (Bi,Pb)2 Sr2 Ca2 Cu2 O10±δ -type and Bi2 Sr2 Ca1 Cu2 O8±Ψ -type compounds. 相似文献
2.
Sara Bals Jo Verbeeck Gustaaf Van Tendeloo Yi-Lin Liu Jean-Claude Grivel 《Journal of the American Ceramic Society》2005,88(2):431-436
The microstructural and compositional evolution during initial annealing of a superconducting (Bi,Pb)2 Sr2 Ca2 Cu3 O10+δ /Ag tape is studied using quantitative transmission electron microscopy. Special attention is devoted to the occurrence of Pb-rich liquids, which are crucial for the Bi2 Sr2 CaCu2 O8+δ to (Bi,Pb)2 Sr2 Ca2 Cu3 O10+δ transformation. Ca and/or Pb-rich (Bi,Pb)2 Sr2 CaCu2 O8+δ grains dissolve into a liquid, which reacts with Ca-rich phases to increase the liquid's Ca-content. This leads to (Bi,Pb)2 Sr2 Ca2 Cu3 O10+δ formation. Apparently, a Ca/Sr ratio of around 1 is sufficient to keep (Bi,Pb)2 Sr2 Ca2 Cu3 O10+δ nucleation going. It is confirmed that Ag particles are transported from the Ag-sheath into the oxide core by the liquid and not by mechanical treatment of the tape. 相似文献
3.
Won-Hyuk Lee Yoshihiro Abe Eikichi Inukai 《Journal of the American Ceramic Society》1993,76(4):849-856
Ag2 O-doped superconducting Bi2 Sr2 Ca1 Cu2 O x ceramics were prepared by a melt-quenching–reheating method. It is found that the Ag2 O-doped, as-cast specimens exhibit superconductivity ( T c = around 80 K) by heat treatment at temperatures around 800°C even in an evacuated and sealed silica glass tube, while the undoped specimens do not and vaporize by the corresponding heat treatment. Conversion of the Ag2 O-doped, as-cast specimens into superconducting ceramics when heated in an evacuated vessel is explained in terms of the oxygen donor of Ag2 O in the specimen. This finding enables us to fabricate a desired shape of superconducting Bi2 Sr2 Ca1 Cu2 O x ceramics sealed in metals or glasses. The addition of Ag2 O to Bi2 Sr2 Ca1 Cu2 O x melt, however, had deleterious influences on the superconducting properties ( T c and J c ) of the resultant ceramics when obtained by heat treatment in air. 相似文献
4.
Suguru Suzuki Shinji Asada Minoru Takahashi Yasuo Hikichi 《Journal of the American Ceramic Society》1991,74(4):714-717
The effect of extrusion on improving the critical current density ( J c ) of Bi1.4 Pb0.6 Sr2 Ca2 Cu3 O x superconducting wires is investigated. Calcined powders (Bi1.4 Pb0.6 Sr2 Ca2 Cu3 O x ) are first mixed with a forming aid—a thermoplastic polymer (polyethylene)—for workability, and then extruded, using a capillary rheometer, to form wires 2 mm in diameter. The J c value, measured by the four-probe method in liquid nitrogen at 77 K, is improved substantially by the following process: (1) the superconducting precursors are extruded at high viscosity with a forming aid, to align the platelike particles unidirectionally; (2) the forming aid alone is carefully burned out, without destroying the extruded configuration; and (3) the extruded wires are annealed at 850°C in air for more than 96 h. 相似文献
5.
Peter J. Majewski Stefanie Kaesche Fritz Aldinger 《Journal of the American Ceramic Society》1997,80(5):1174-1180
Phase equilibria of the quasi-quinary system Bi3 O3 -PbO-SrO-CaO-CuO were studied between 650° and 900°C in air with emphasis on the high-temperature superconducting phase (Bi,Pb)2+ x Sr2 Ca2 Cu3 O10+ d (2223). The 2223 phase lies in equilibrium with a number of nonsuperconducting phases and also with the superconducting phase (Bi,Pb)2 Sr2 CaCu2 O8+ d (2212). The single-phase region was found to be very limited. The Pb solubility of the 2223 phase is strongly temperature dependent. The phase relations are very sensitive to variations of the cation concentration and temperature. This effect significantly influences the preparation of 2223 ceramics. 相似文献
6.
Retrograde densification of pelletized calcines and glasses having an approximate (Bi,Pb)2 Sr2 Ca2 Cu3 O10 starting stoichiometry and sintered at ∼850°C can be described by first-order rate equations. Retrograde densification in the calcine precursors was largely due to the development of open pores, and was approximately proportional to the concentration of the (Bi,Pb)2 Sr2 CaCu3 O10 phase. In the glasses, retrograde densification is mainly caused by porosity accompanying the growth of a needlelike Sr─Ca─Cu─O phase, together with (Bi,Pb)2 Sr2 Ca2 Cu3 O10 and (Bi,Pb)2 Sr2 CaCu2 O8 . 相似文献
7.
Takayuki Komatsu Michiko Ueta Tomohiro Ohki Ryuji Sato Kazumasa Matusita 《Journal of the American Ceramic Society》1992,75(7):1864-1869
The Ba-doped superconducting (Bi,Pb)2 Sr2- x Ba x Ca2 Cu3 O y and (Bi,Pb)2 Sr2 Ca2- x Ba x Cu3 O y (0 ≦ x ≦ 1.0) were prepared by using a melt-quenching method, and the effect of Ba additions on the glass-forming ability and the crystalline phase was examined. The glass-forming ability was not improved by substitution of Ba for Sr or Ca, and particularly BaPbO3 as well as CaO was observed in the melt-quenched sample of (Bi,Pb)2 SrBaCa2 Cu3 O y . BaPbO3 crystals were precipitated in all glass-ceramics with Ba substituted for Sr or Ca. The partial substitution of Ba substituted for Sr was effective for the formation of the high- T c phase, and (Bi,Pb)2 Sr1.4 Ba0.6 Ca2 Cu3 O y glass-ceramics obtained by annealing at 830°C for 100 h exhibited superconductivity with a T c of 103 K, although BaPbO3 and the low- T c phase were still largely present. 相似文献
8.
Al2 O3 addition to the melt of a BiSrCaCu2 O x composition was found by TEM observation to cause the liquid-liquid phase separation of the melt-quenched glass, and to result in preferential precipitation of superconducting Bi2 Sr2 Ca1 Cu2 O x crystals from the melt during the cooling process. 相似文献
9.
Phase equilibria of the La2 O3 –SrO–CuO system have been determined at 950°C at 30 kbar (3 GPa). Stable phases at the apexes of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 , CuO4 and La2 Cu2 O5 in the LaO1.5 –CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO–SrO binary. The La2– x Sr x -CuO4–δ solid solution is stable for 0.00 is ≤ x ≤ 1.29, the La2– x Sr1+ x Cu2 O6+δ solid solution is stable for 0.03 ≤ x ≤0.20, the La2– x Sr x Cu2 O5–δ solid solution is stable for 0.00 ≤ x ≤1.08, and the La x Sr14– x Cu24 O41 solid solution is stable for 0.00 ≤ x ≤ 6.15. The 30 kbar phase diagram differs from the 1 atm (0.1 MPa) and 10 kbar (1 GPa) results principally in the absence of La1– x Sr2+ x Cu2 O5.5+δ as a stable phase and the extended range of the La2– x Sr x Cu2 O5–δ solid solution at 30 kbar. 相似文献
10.
The phase diagram for the CuO-rich part of the La2 O3 ─CuO join was redetermined. La2 Cu2 O5 was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu7 O19 had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La2 O3 ─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La1.9 Ca1.1 Cu2 O5.9 and LaCa2 Cu3 O8.6 , were stable at these temperatures, with three binary phases, Ca2 CuO3 , CaCu2 O3 , and La2 CuO4 . La2 Cu2 O5 and La8 Cu7 O19 were stable only at 1020°C, and did not support solid-solution formation. 相似文献
11.
Phase equilibria of the La2 O3 -SrO-CuO system have been determined at 950°C and 10 kbar (1 GPa). Stable phases at the apices of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 CuO4 in the LaO1.5 -CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO-SrO binary. The La2-x Sr x CuO4-δ solid solution is stable where 0.0 ≤ x ≤ 1.3, the La2-x Sr1+x Cu2 O6+δ solid solution is stable where 0.0 ≤ x ≤ 0.2, the La8-x Sr x Cu8 O20-δ solid solution is stable where 1.3 ≤ x ≤ 2.7, the La x Sr14-x -Cu24 O41 solid solution is stable where 0 ≤ x ≤ 6, and the La1+x Sr2-x Cu2 O5.5+δ phase is stable where 0.04 ≤ x ≤ 0.16. The La2 O3 -SrO-CuO phase diagram at 950°C and 10 kbar is almost identical to that determined by other authors at 950°C and 1 atm, in terms of phase stability and solid-solution ranges. 相似文献
12.
Winnie Wong-Ng Robert S. Roth Claudia J. Rawn 《Journal of the American Ceramic Society》1997,80(2):324-328
Single-crystal X-ray diffraction was used to investigate the structure of the ternary oxide of approximate formula Bi14 (Sr,Ca)12 O33 . The crystal examined was found to have a composition Bi2 Sr0.68 Ca1.07 O4.75 or Bi16 Sr5.44 Ca8.56 O38 as a result of refinement. It crystallizes in the monoclinic space group (C2/m), with cell parameters a = 21.764 (4) A, b = 4.3850 (13)° A, c = 12.905 (3) A, β= 102.72 (2)°, and V 1201.2 (5) A3 . Strontium and calcium ions were found to substitute for each other. The structure consists of a network of alkaline-earth oxide polyhedra with broad channels parallel to the b axis, in which the bismuth ions reside. Two out of four crystallographically distinct Bi ions form infinite Bi—O zigzag ribbons of edge-linked Bi—O units, while each of the other two form oxygen corner-shared Bi—O chains along b . The lone pair electrons of the Bi ions point toward each other in the channels. 相似文献
13.
The Bi2 O3 –Nb2 O5 –NiO phase diagram at 1100°C was determined by means of solid-state synthesis, X-ray diffraction, and scanning electron microscopy. A ternary eutectic with a melting point below 1100°C was found to exist in the field between NiO, Bi2 O3 , and the end-member of the δBi2 O3 –Nb2 O5 solid solution. The existence of the previously reported Bi3 Ni2 NbO9 phase was disproved. A pyrochlore homogeneity range around Bi1.5 Ni0.67 Nb1.33 O6.25 was determined together with all the phase relations in this phase diagram. 相似文献
14.
Thin films of Baz Ca2 Cu3 O7 a precursor of TIBa2 , Ca2 -Cu3 O9-y , were prepared by sol-gel synthesis from an all alkoxide solution. The barium and calcium precursors were the respective metals reacted with 2-methoxyethanol, and the copper precursor was copper methoxide complexed by triethanolamine. Silver substrates were coated using the sol-gel solution by dip-coating. Subsequent processing included a low-temperature drying step (600°C), repeated coating to provide the desired thickness, heat treatment at 850°C in oxygen to remove carbon, and reaction at 860°C in a two-zone thallination furnace to produce a TIBa2 Ca2 -Cu3 O9-y , superconducting film. These films were strongly c-axis-aligned, had a zero-resistance temperature (T2 ) of 110 K, and a critical-current density (Jc ) of 1.9 × 104 A/cmZ at 77 K and zero magnetic field. 相似文献
15.
Solid-state reactions of equimolar mixtures of Bi2 O3 and Fe2 O3 from 625° to 830°C and their kinetics were investigated. The reaction rates were determined from the integrated X-ray diffraction intensities of the strongest peaks of the reactants and products. The activation energy for the formation of BiFeO3 was 96.6±9.0 kcal/mol; that for a second-phase compound, Bi2 Fe4 O9 , which formed above 675°C, was 99.4±9.0 kcal/mol. Specific rate constants for these simultaneous reactions were obtained. The preparation of single-phase BiFeO3 from the stoichiometric mixture of Bi2 O3 and Fe2 O3 is discussed. 相似文献
16.
Ag-sheathed (Bi,Pb)2 Sr2 Ca2 Cu3 O, (2223) tapes were made by the oxide-powder-in-tube method. Tapes were heat-treated isothermally at several different temperatures in 7.5% O2 /Ar, then quenched into oil to retain the phase assemblages at the reaction temperatures. 2223 formed between ∼810° and ∼837°C. The Avrami equation was applied to describe the kinetics of 2223 formation from a mixture of Bi2 Sr2 CaCu2 O x and nonsuperconducting phases, mainly Ca2 PbO4 and CuO. The calculated Avrami exponent, n ∼ 1, indicated that the kinetics in this system could be described as a diffusion-controlled, two-dimensional nucleation and growth process. The apparent activation energy for forming 2223 was ∼2900 kJ/mol from ∼817° to ∼825°C and ∼890 kj/mol from ∼825° to ∼837°C. A temperature-time-transformation diagram was constructed based on the kinetic data; it describes the transformational behavior of this particular system. 相似文献
17.
We report the enhancement of the zero resistivity T c(0) by 5.5 K i.e. from 104 to 109.5 K by substitution of gallium 1.34% of copper in the bismuth 2223 compound. A series of Ga-containing compounds Bi2 Pb0.4 Sr2 Ca2 Cu3− x Ga x O y ( x =0.00, 0.02, 0.04, 0.06, and 0.08) are synthesized by the solid-state reaction method. The samples are characterized by measurements of their dc electrical resistivity and ac magnetic susceptibility and by the powder X-ray diffraction analysis. It is noted that the high- T c (2223) phase increases from 57.55% in an undoped sample to 92.99% in samples containing a low concentration of gallium i.e. x ≤0.04. 相似文献
18.
Jacob Koshy Krishnan Sudarsana Kumar Jose Kurian Yogendra P. Yadava Alaatoor D. Damodaran 《Journal of the American Ceramic Society》1995,78(11):3088-3092
A new group of complex perovskites, REBa2 SnO5.5 (where RE = Pr, Sm, Eu, and Gd) have been synthesized and sintered as single-phase materials with high sintered density and stability by the solid-state reaction method. The structure of REBa2 SnO5.5 was studied by the X-ray diffraction technique, and all of them were found to be isostructural and have a cubic perovskite structure. The dielectric constant and loss factor values of these materials are in a range suitable for substrate applications. The X-ray diffraction and resistivity measurements have shown that there is no detectable reaction between YBa2 Cu3 O7-δ and REBa2 SnO5.5 , even when the substances are mixed thoroughly and sintered at 950°C for 15 h. Thick films of YBa2 Cu3 O7-δ fabricated on polycrystalline REBa2 SnO5.5 substrates gave superconducting zero resistivity transition T C(0) = 92 K, indicating the suitability of these new materials as substrates for YBa2 Cu3 O7-δ films. 相似文献
19.
The thermodynamic data for the Y2 O3 –BaO–Cu2 O–CuO quaternary system were optimized from measured thermodynamic data. A two-sublattice model for ionic solution was used to express the Gibbs free energy of the liquid phase, and a two-sublattice regular solution model was used for the nonstoichiometric YBa2 Cu3 O6+δ superconducting compound. The optimized thermodynamic data were used to calculate the phase diagrams of the Cu2 O–CuO binary system and the CuO x –Y2 Cu2 O5 and CuO x –BaCuO2 quasi-binary systems. The results were in good agreement with reported measured data. The liquidus projection and isothermal and vertical sections of the Y2 O3 –BaO-CuO x quasi-ternary system were calculated. The effect of oxygen pressure on some reaction temperatures was predicted by calculating them at various oxygen pressures, and the oxygen contents (6 +δ) in YBa2 Cu3 O6+δ were calculated at various temperatures and oxygen pressures. The results were compared with experimental data. 相似文献
20.
Hilde Lea Lein Kjell Wiik Mari-ann Einarsrud Tor Grande Edgar Lara-curzio 《Journal of the American Ceramic Society》2006,89(9):2895-2898
Steady-state compressive creep rate of La0.5 Sr0.5 Fe0.5 Co0.5 O3−δ (LSFC) and La0.5 Sr0.5 CoO3−δ (LSC) is reported in the temperature region 900°–1050°C and stress range 5–28 MPa. The stress exponents for the two materials were 1.71±0.18 and 1.24±0.15, respectively. The activation energy for creep was considerably higher for LSC (619±56 kJ/mol) than for LSFC (392±28 kJ/mol). The grain size exponent for LSC was 1.28±0.14. Considerably higher creep rates were observed for both materials in N2 compared with air. Relaxation by creep of chemical-induced stresses in oxygen-permeable membranes is addressed, especially at low partial pressure of oxygen. 相似文献