共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Horng-Show Koo George C. Tu Tseung-Yuen Tseng 《Journal of the American Ceramic Society》1994,77(1):27-32
The present work reports that highly c -axis-oriented Tl-Ba-Ca-Cu-O superconducting films with zero-resistance temperature up to 112 K were successfully prepared using the spray pyrolysis technique with a subsequent Tl-diffusion treatment. The insalating Ba-Ca-Cu-O precursor films (Ba:Ca:Cu = 2:2:3) were made by spray deposition of the related metal nitrate solution on a preheated (300°–400°C) MgO(001) single-crystal substrate. The presence of the superconducting phases of the resultant films depended strongly on the types of Tl sources used. The results showed that the formation of the super conducting phases could be achieved more readily by using the bulk Tl-Ba-Ca-du-O rather than Tl2 O3 as a Tl source. In other words, the low Tl content in the TlBaCaCuO bulk source with a resulting low Tl-vapor pressure is favorable for the formation of a higher T c superconducting phase. The dominant phases in the prepared films were mainly TlBa2 Ca2 Cu3 O/(1223 phase) and Tl2 Ba2 CaCu2 Oy (2212 phase). The critical current density of a film with a nearly single-phase(1223) structure was measured to be 1.2 × 104 A/cm2 at 77 K under zero magnetic field. 相似文献
3.
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
4.
The cation solubility limits of the n = 2 and n = 3 superconducting phases in the Bi2 (Sr x Ca1 − x ) n +1 Cu n O y system were established along tie lines with compatible phases via electron probe microanalysis on bi- (or poly-) phasic samples prepared at 860°C. Pb additions (15 mol% of the Bi content) were used to facilitate formation of the n = 3 phase. In each case football-shaped volumes in composition space were established as the solubility limits which bordered on the nominal compositions 2212 or 2223 (Bi:Sr:Ca:Cu) with the long axis parallel to the Sr-Ca side of the quaternary (i.e., Sr-to-Ca intersolubility) but also extending toward Bi and Cu. This means that, for the most part, the superconducting phases are alkaline-earth deficient relative to the ideal 2212 and 2223 compositions. The Pb content in the 2223 phase is typically 10% of the Bi content. T c variations could be correlated with variations in Sr or (Sr + Bi) content and the length of the c -axis parameter. 相似文献
5.
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
6.
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
7.
The phase equilibria near (Bi,Pb)2 Sr2 Ca2 Cu3 O10+delta ((Bi,Pb)-2223) was studied in the temperature range of 750°-820°C in air and in reducing atmospheres. In air, (Bi,Pb)-2223 was in equilibrium with one or more of the following phases: (Bi,Pb)2 Sr2 CaCu2 O8+delta ((Bi,Pb)-2212), (Sr,Ca)14 Cu24 O41 (14:24), (Ca,Sr)2 CuO3 , (Bi,Pb)4 (Sr,Ca)5 -CuO x (451), Ca2 PbO4 , and CuO. Ca2 PbO4 and the 451 phase were not in equilibrium with (Bi,Pb)-2223 at an oxygen partial pressure ( p O2 ) of 10-3 atm, which is indicative of higher lead solubility in (Bi,Pb)-2223 under more-reducing conditions. In a second set of experiments, the lead content in both (Bi,Pb)-2212 single crystals and (Bi,Pb)-2223 powders was investigated as a function of p O2 at a constant temperature of 750°C. Lead solubility in (Bi,Pb)-2212 and (Bi,Pb)-2223 increased as p O2 decreased. 相似文献
8.
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
9.
The formation of superconducting phases in the Bi(Pb)─Sr─Ca─Cu─O system has been systematically investigated using DTA/TG, XRD, SEM/EDAX, TEM, EPMA, ICP-AES, fourprobe dc resistance, and ac susceptibility. Starting compositions, firing temperature, and the duration of heat treatment, together with the atmosphere, were found to be critical in determining the preferred formation of the 2223 phase. This paper reports the effect of the initial chemical composition, emphasizing the importance of compositional control in the synthesis of the single 2223 phase. It has been shown that, with a correct starting composition and predetermined synthesis conditions, single 2223 phase can be obtained without intergrowth by the 2212 and other impurity crystalline phases. The optimum starting composition for the preferred growth of the 2223 phase was identified as being Bi1.7 Pb0.3+ y Sr2 Ca2 Cu3 O x ( y = 0.1), with excess Pb added in order to compensate for its loss at high temperatures. The effect of Pb doping and excess Cu on the phase formation in the Bi oxide based superconducting system is discussed. 相似文献
10.
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
11.
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
12.
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
13.
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
14.
Winnie Wong-Ng Lawrence P. Cook Boris Paretzkin Michael D. Hill Judith K. Stalick 《Journal of the American Ceramic Society》1994,77(9):2354-2362
Crystal chemistry and subsolidus phase equilibrium studies of the Ba-Nd-Cu-O system near the CuO and Nd2 O3 corners have been carried cut at 950°C in air. Two solid-solution series have been identified in the Ba-Nd-Cu-O system. The first series involves the high- T c superconductor phase, and has the formula Ba2–x Nd1+x Cu3 O6+z , where × < ≅ 0.7. At the ideal compound stoichiometry of Ba2 NdCu3 O6+z , the transformation from the high- T c orthorhombic to tetragonal phase occurs at 550°–575°C in air. This temperature varies as a function of composition, and at x ≅ 0.2 to 0.3 it occurs at 950°C. The second solid solution is the non-superconducting "brown phase" represented by Ba2+2x -Nd4–2x Cu2–x O10–2z 0 ≤ x ≤ 0.1. Preliminary phase diagrams of the BaO–Nd2 O3 and Nd2 O3 –CuOx systems are also presented. Standard X-ray diffraction patterns of BaNd2 –CuO5 and (Nd1.9 Ca0.1 )CuO4–z are provided. 相似文献
15.
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
16.
Ji-Ping Zhou Charles C. Sorrell Shi-Xue Dou Miles H. Apperley 《Journal of the American Ceramic Society》1991,74(7):1541-1546
The present work describes a new technique to synthesize aligned YBa2 Cu3 O7- x and Ag─YBa2 Cu3 O7- x superconducting composites from Ba- and Cu-deficient compositions (relative to YBa2 Cu3 O7- x ) plus BaCuO2 . For YBa2 Cu3 O7- x , high transition temperature midpoint Tc (91 K), temperature of zero resistivity T 0 (90 K), and critical current density Jc (>3000 A°Cm−2 at 77 K) were achieved by using this technique. This procedure provides the potential for using a reliable and reproducible densification and alignment technique alternative to partial or full melting. The composite is highly aligned, with an average grain size of ∼1 to 2 mm and domains of width greater than 5 mm. The initial phase assemblage consists of YBa2 Cu3 O7- x (123) as the major phase plus YBa2 CuO5 (211) CuO as minor phases. The BaCuO2 is added to the Ba- and Cu-deficient starting composition in order to assist in the formation of a CuO-rich liquid as well as to compensate for the Ba and Cu deficiences in 123. Since the liquid forms at ∼900°C and is compatible with 123, it can be used to facilitate alignment of 123 at ∼930°C. The addition of Ag to the system results in eutectic formation with the (solidified) liquid, substantial filling of the pores during sintering, and improved alignment. 相似文献
17.
Solid-state sintering was used to make YBa2 Cu3 O7−δ superconducting bulk materials. Corrosion of the YBa2 Cu3 O7−δ superconductor material was investigated in a humid environment. The superconducting materials exhibited significant corrosion after 4 h at 80° and 100% relative humidity. A grain-boundary phase was formed, and the percent superconducting phase in the material decreased by approximately 60%. The transition temperature (Tc ) decreased with corrosion time. After 2 h of corrosion, Tc decreased from 87 to 81 K. 相似文献
18.
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
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.
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