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1.
A Bi-Pb-Sr-Ca-Cu oxide superconducting thick film, exhibiting Tc(onset) = 120 K and Tc(zero) = 100 K, can be obtained by spray pyrolysis of oxalate suspension on the (100) MgO substrate, using the partial-melting state at 860°C for 15 h, a rapid-quenching process to 500°C, and a postannealing treatment for 1 h at 835°C. These processes are believed to enhance the volume fraction of 2223 phase and increase the Tc(zero) . The films show preferred orientation and adhere well to the substrate. 相似文献
2.
Atomistic lattice simulations are reported of the normalstate crystal properties of high- T c oxides. Nonstoichiometry in La2 CuO4 and Nd2 CuO4 associated with oxygen interstitial defects is examined in some detail. The lattice structure and defect chemistry of Ca2 CuO3 , Sr2 CuO3 , La2 SrCu2 O6 , and Sr2 CuO4 are also considered. Finally, Jahn-Teller effects and bipolaron formation are addressed in relation to high- T c behavior. 相似文献
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4.
The high-Tc superconducting oxide Yba2 Cu3 O7–y has been prepared by the amorphous citrate process. A citrate-nitrate solution was prepared at room temperature and dehydrated at around 80°C to yield a solid precursor material. The precursor was fired to high temperature to form the desired compound. The decomposition mechanism was studied with thermogravimetric analysis and X-ray diffraction. Intermediate products were formed during the decomposition reactions. Nearly phase-pure Yba2 Cu3 O7-y powders were obtained by firing the precursor in air to 900°Cfor2 h. Sintered samples were typically over 90% dense and exhibited good superconducting properties. 相似文献
5.
Keiji Kobayashi 《Journal of the American Ceramic Society》1990,73(1):146-147
Experimental data for maximum T c , up to 125 K with temperature cycling, are reported with regard to Y-Ba-Cu-O.OH systems. This increase in T c is presumably associated with structural transition or phase equilibrium for [CuO6 ] local octahedra, occupied by hydroxyl or fluorine ions in the oxygen vacancy sites. Possible improvement in T c using hydroxide ceramic compounds is described briefly. 相似文献
6.
A superconducting line should be essentially lossless and dispersionless and have a purely resistive impedance up to at least 10 GHz. In fact we expect that a long (>1 km) line could carry nanosecond rise time pulses with zero distortion and low loss (<1 dB/km). We have measured the losses in some short sections of coaxial line containing ceramic high-Tc superconducting-center conductors over the frequency range from 5 to 50 MHz. There is only a slight improvement over a completely copper coaxial line. 相似文献
7.
Microstructure and properties of high- T c Ba2 YCu3 O7- x ceramics were studied as a function of purity of raw materials and processing conditions. Technical-grade (TG) and reagent-grade (RG) raw materials were used to prepare the precursor superconducting powders, the characteristics of which were monitored by XRD, chemical analysis, and SEM. Bulk specimens were then prepared with the two master batches. XRD microphase analysis and SEM-EDS investigation did not show phase differences. J c and normal-state resistivity measurements indicated that the TG specimens had more resistive grain boundaries than did RG specimens. 相似文献
8.
High-Tc superconductor wire and sheet were fabricated by electrophoretic deposition of superconductor powders on silver-metal substrates followed by an appropriate sintering schedule. The technique has some promise for technological applications. 相似文献
9.
Chan Joong Kim Suk-Joong L. Kang Dong-Yeon Won 《Journal of the American Ceramic Society》1992,75(3):570-574
Compact swelling in Pb-doped Bi-Sr-Ca-Cu-O superconductor has been studied by observing the effects of the size of calcined powders, volatilization of materials, and sintering of high- T c (2223) powders. The bulk density increases at the early stage of sintering, for about 20 h, and then decreases. Densification occurs when the low- T c (2212) phase and a liquid phase exist, whereas dedensification occurs with the formation of the 2223 phase regardless of the presence of the liquid. Gas evolution from specimens does not appear to be responsible for compact swelling. Compact swelling is explained by anisotropic growth of thin, platelike 2223 grains in random orientation. When 2223 grains grow in a preferred direction, compact swelling is suppressed. 相似文献
10.
Kevin J. Leary Howard W. Jacobson Thomas R. Askew Richard B. Flippen 《Journal of the American Ceramic Society》1990,73(4):904-908
The elemental homogeneity of YBa2 Cu3 O7 powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950°C), followed by annealing in oxygen above 750°C, and slow cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO2 -treated powder, as measured by ac susceptibility. Moreover, the NO2 -processed powder exhibits a slablike morphology which should be more suitable for grain alignment. A substantial advantage of the NO2 process is that this process is easily scaled to larger batches and the results are highly reproducible. This is not the case for solid-state reaction processes requiring repeated heating and grinding. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO3 )2 which acts as a flux that dissolves the constituents and reprecipitates them as highpurity YBa2 Cu3 O7 . The effects of the various process variables on the properties of the treated powder, and the reproducibility of the process, are discussed. 相似文献
11.
Ying-Chung Chen Kwok-Keung Chong Teen-Hang Meen Long Wu Mau-Phon Houng 《Journal of the American Ceramic Society》1991,74(7):1710-1714
The effect of humidity on the bismuth superconductor is investigated under 90% humidity at 30°C for 250 h. Nearly none of the peaks of high- T c phase (2223) can be observed in the X-ray pattern after the test. The silver contact resistance of the sample also increases prominently in the time interval from 60 h to 100 h. When the humidity-tested sample is heated again under sintering conditions (845°C for 50 h in air), the high- T c phase appears again. 相似文献
12.
Metal Dopants in Bi-Pb-Ca-Sr-Cu-O High-Tc Superconductor Thick Films Prepared by Melt Solidification
Masahiro Tatsumisago Hisashi Chigusa Noboru Tohge Tsutomu Minami 《Journal of the American Ceramic Society》1992,75(1):231-233
Metal-doped superconductor thick films Bi1.6 Pb0.4 M0.1 Ca2 -Sr2 Cu3 Ox (M = V, Nb, Mo, In, Sn, Sb, and W) were prepared using a melt–solidification procedure. The optimum heat-treatment temperature T opt was observed in all the films with different dopants; T opt was related to the temperature at which a partial melting of the films occurred as determined by differential thermal analysis. The dopants in the melt-solidified films lower the partial melting temperature and thus lower T opt for the formation of the 110 K phase. 相似文献
13.
The decomposition products of YBa2 Cu3 O7-x depend on the composition of the molten chloride salt for exposure at 1173 K in air. The presence of dichloride salts such as CuCl2 , CaCl2 , or MgCl2 promote formation of CuO, Cu2 Y2 O5 , and loss of barium to the chloride salt as BaCl2 . Salts based on BaCl2 or containing LiCl result in YBa2 Cu3 O7-x decomposition products of Y2 BaCuO5 , CuO, and BaCl2 . High barium activity in the salt supports formation of the Y2 BaCuO5 phase and reaction of CO2 with the salt producing BaCO3 . Decomposition is most sluggish in binary NaCl-KCl salts where minimal amounts of reaction or decomposition products are observed. 相似文献
14.
Takahiro Wada Nobuo Suzuki Hisao Yamauchi Shoji Tanaka Atsutaka Maeda Kunimitsu Uchinokura 《Journal of the American Ceramic Society》1989,72(10):2000-2003
The relationship between the preparation procedure and superconducting properties of La1 Ba2 Cu3 Oy was studied. A series of samples was sintered in an N2 -gas atmosphere for various lengths of time ranging from 1 to 40 h, followed by a fixed annealing procedure in O2 . It was found that the shorter the sintering period, the higher was the oxygen content. The samples sintered for a period of less than 15 h contained excess oxygen compared with La1 Ba2 Cu3 O7 and exhibited poor superconducting properties. The sample sintered for 40 h had an oxygen content y equal to 6.95, and had excellent superconducting properties. The mechanism for preparing high-quality La1 Ba2 Cu3 Oy is discussed. 相似文献
15.
Sintering YBa2 Cu3 O7- x bulk forms at 1050°C followed by annealing at 980°C causes the development of a thick oriented surface layer (Lotgering factor = 0.7). The thickness of the layer depends on the thermal treatment, which is a two-step sintering process. Firing at 1050°C for 2.5 h followed by 30 h at 980°C leads to the development of a 0.1-mm-thick surface layer, with clear indication that longer annealing would result in a thicker film. Some orientation develops during un-axial compaction of the powders. Lotgering orientation factor calculation from X-ray diffraction analysis. SEM, and TEM were used to characterize the microstructure of these samples. T c was similar to that of conventionally processed high-density samples, between 83 and 87 K. Some thermal treatments resulted in samples that displayed high resistivity above T c , possibly caused by segregation of Cu to the grain boundaries. 相似文献
16.
Lorraine Falter Francis David A. Payne 《Journal of the American Ceramic Society》1991,74(12):3000-3010
Thin layers of Pb[(Mg1/3 Nb2/3 )1– x Ti x ]O3 (PMNT) were prepared by spin casting alkoxide-based solutions on platinized Si. The effects of additives, heat treatment, and composition ( x = 0 to 0.9) on perovskite phase development, ceramic microstructure, and dielectric properties are reported. Depending upon the processing conditions, ceramic thin layers could be formed in a nonferroelectric pyrochlore phase (A2 B2 O6 ) or in a ferroelectric perovskite phase (ABO3 ). The dimensions of the pyrochlore and perovskite units cells were related and increased with Mg and Nb contents. To minmize pyrochlore formation, the most effective processing method involved rapid heat treatment between successive solution depositions. Phase development and microstructure were also affected by solution additives. Additions of benzoic acid were found to affect the structure in solution and the later organic pyrolysis behavior from thin layers. The effect of composition on the dielectric and ferroelectric properties is also reported. 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.
David W. Johnson Jr. Warren W. Rhodes 《Journal of the American Ceramic Society》1989,72(12):2346-2350
Bi2 Sr2 CaCu2 O8 was prepared using the mixed oxide-carbonate method and sintered at temperatures ranging from 850° to 911°C. The samples were characterized for density, mechanical strength, phase composition, microstructure, and superconducting transition temperatures. A unique retrograde densification characteristic is demonstrated in the temperature range 850° to 890°C whereby the material first becomes less dense as the sintering temperature is raised, and only in a narrow temperature range from 900° to 905°C does the material densify then with the formation of a liquid phase. The retrograde densification mechanism is shown to be that of the formation of thin platelike crystallites which grow in a randomly oriented fashion, thus pushing the structure apart. This retrograde densification, coupled with a narrow sintering range overlapping the melting temperature, makes this compound a difficult one to process. 相似文献
19.
Joseph R. Spann Isabel K. Lloyd † Manfred Kahn Mark T. Chase ‡ 《Journal of the American Ceramic Society》1990,73(2):435-438
A single calcination step, solid-state process that provides orthohombic Ba2 YCu3 O7 powder is described. BaCO3 , Y2 O3 , and CuO are used as precursor materials. The only phase identifiable by X-ray diffraction is the orthorhombic Ba2 YCu3 O7 . The use of a vacuum during the inital stages of the calcining process promotes complete decomposition of the carbonate, and no residual carbonate is observed. An oxygen atmosphere during the later stages of calcining ensures proper oxidation to Ba2 YCu3 O7 . The use of a similar combination vacuum-oxygen calcining schedule should also be beneficial in the preparation of chemically derived powders. 相似文献
20.
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