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1.
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
2.
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
3.
Krzysztof Borowiec Jan Przyluski Krystyna Kolbrecka 《Journal of the American Ceramic Society》1991,74(8):2007-2010
The intrinsic kinetics, unaffected by diffusional and masstransfer effects, of the CO2 degradation of superconducting particles have been determined using a nonisothermal technique. Below 900°C, the carbonization of YBa2 Cu3 O7- x leads to formation of BaCO3 , Y2 Cu2 O5 , CuO, and Cu2 O. A further increase in temperature results in formation of BaCuO2 from BaCO3 and CuO. The carbonization rate shows the 1.5th-order dependence on the amount of unreacted YBa2 Cu3 O7- x for the temperature range of 550° to 815°C. The activation energy of carbonization was determined to be 95.1 kJ · mol−1 . 相似文献
4.
Phase equilibria in the CaO-CuO system have been determined at 1 atm pressure in oxygen over the temperature range 800° to 1300deg; C. CaO is the stable phase at the calcium-rich end of the system. Two intermediate crystalline phases, namely Ca2 CuO3 and Ca3 Cu7 O10 , form. Caz CuO3 is stable up to 1085°± 3deg; C, where it melts incongruently to CaO + liquid (peritectic liquid has ε82% CuO). Ca3 Cu7 O10 becomes stable at 977°± 3deg; C by reaction between Ca2 CuO3 and CuO. Ca3 Cu7 O10 melts incongruently at 1046°± 3deg; C to Ca2 CuO3 + liquid (peritectic liquid has ε83% CuO). CuO is the stable copper oxide phase up to 1061°± 3deg; C at the copper-rich end of the system; at higher temperatures, Cu2 O is stable until the liquidus is reached at 1121deg; C. The binary eutectic is at 1045°± 5deg; C, in which a liquid with 83% CuO coexists with Ca3 Cu7 O10 and CuO. 相似文献
5.
Jean-Pierre Lawanier James K. Meen Don Elthon 《Journal of the American Ceramic Society》1996,79(2):533-535
Phase equilibria in the YO1.5 BaO-CuO system have been determined at 950°C at 10 kbar using a piston-cylinder apparatus. The oxide phases stable under these conditions are Y2 O3 , Y2 Cu2 O5 , CuO, Y2 BaCuO5 , YBa2 Cu3 O6.5 , BaCuO2 , Y2 BaO4 , Y2 Ba3 O6 , and YBa4 Cu2 O7.5 . The phase stabilities observed at 950°C at 10 kbar are identical to those observed at 950°C in air or oxygen at 1 atm for compositions with <40% Ba of the cations. In more Ba-rich portions of the phase diagram, carbonates and oxycarbonates are stabilized and a systematic determination of the phase equilibria has not been successful. 相似文献
6.
Teen-Hang Meen Ying-Chung Chen Ken-Whie Liaw Hung-Duen Yang 《Journal of the American Ceramic Society》1993,76(8):1948-1952
X-ray diffraction patterns show that most samples of Y1-x Prx Ba2 Cu4 O8 examined in the present study contained a single YBa2 Cu4 O8 (1-2-4) superconductive phase for x<0.7.Lattice parameters a and b increased with Pr concentration, suggesting that most of the Pr is trivalent in Y1-x Prx- Ba2 Cu4 O8 . The zero-resistance temperature, T co , decreases monotonically from 80 K at x=0 to 12 K at x=0.65, and superconducting transition widths tend to broaden for x>0. The room-temperature resistivity changes linearly until x=0.7 and increases abruptly at x=-0.75. The critical concentration, xcr , thus was estimated to be 0.7. The effective magnetic moments of Pr in Y 1-x Prx Ba2 Cu4 O8 were 3.63., 3.35, and 3.23, μB for x=0.2, 0.4 and 0.6, respectively. In the R0.8 Pr0.2 Ba2 Cu4 O8 system, the depression of Tc weakly depends on the ionic radius of rare-earth elements. Similarities and differences between Y 1-x Prx Ba2 Cu4 O8 and Y1-x Prx- Ba2 Cu3 O7-y also were noted and are discussed in this paper. 相似文献
7.
Eric L. Brosha Fernando H. Garzon Ian D. Raistrick Peter K. Davies 《Journal of the American Ceramic Society》1994,77(5):1139-1142
The low-temperature phase relations in the Y-Cu-O system were examined using ultrasonically prepared, freeze-dried nitrate precursors. Under 1 atm of oxygen, Y2 Cu2 O5 was found to be stable above 955 ± 5 K; below this temperature, the component binary oxides CuO and Y2 O3 are the only stable phases in the system. The entropy of formation of Y2 Cu2 O5 , with respect to the component oxides, was calculated to be 5.3 ± 2.3 J/(mol.K) at 955 K. Bond valence analyses indicate that the entropy stabilization of this compound is most likely caused by the underbonded character of the copper ions. 相似文献
8.
Janine C. Borofka Bryan C. Hendrix Abbas I. Attarwala John K. Tien 《Journal of the American Ceramic Society》1993,76(4):1011-1016
Hot isostatic pressing (HIP) can be used to produce fully dense shapes of high-temperature ceramic superconductors. Densification modeling of monolithic YBa2 Cu3 O7-δ and the composite YBa2 Cu3 O7-δ /Ag systems allows an understanding of the HIP process and has led to the development of successful protocols for HIP of these materials. Ag metal is the best encapsulation material found for both systems. HIP of monolithic YBa2 Cu3 O7-δ requires a slow ramp of pressure in order to prevent decomposition into more basic oxides such as Y2 BaCuO5 and CuO. HIP of composite YBa2 Cu3 O7-δ /Ag requires careful powder processing to obtain dense material with a fine dispersion of Ag. 相似文献
9.
The standard Gibbs free energies of formation of CuAlO2 and CuAl2 O4 were determined in the range 700° to 1100°C, using emf measurements on the galvanic cells (1) Pt,CuO +] Cu2 O/CaO-ZrO2 /O2 ,Pt; (2) Pt,Cu +] CuAlO2 +] Al2 O3 /CaO-ZrO2 / Cu +] Cu2 O,Pt; and (3) Pt,CuAl2 O4 +] CuAlO2 +]Al2 O3 /CaO-ZrO2 /O2 ,Pt. The results are compared with published information on the stability of these compounds. The entropy of transformation of CuO from tenorite to the rock-salt structure is evaluated from the present results and from earlier studies on the entropy of formation of spinels from oxides of the rock-salt and corundum structures. The temperatures corresponding to 3-phase equilibria in the system Cu2 O-CuO-Al2 O3 at specified O2 pressures calculated from the present results are discussed in reference to available phase diagrams. 相似文献
10.
Eric L. Brosha † Fernando H. Garzon Ian D. Raistrick Peter K. Davies 《Journal of the American Ceramic Society》1995,78(7):1745-1752
Ultrasonically prepared freeze-dried nitrate precursors and high-precision solution calorimetry were used to investigate the low-temperature thermodynamic stabilities of compounds in the Y-Cu-O, Ba-Cu-O, Y-Ba-O, and Y-Ba-Cu-O pseudobinary and pseudoternary systems at 1 atm of oxygen. Y2 Cu2 O5 , Y2 BaCuOs , and BaCuO2 were found to be metastable below 682°, 728°, and 710°± 5°C, respectively. The only stable phases in the Y-Ba-Cu-O system at 298 K and 1 atm of oxygen are Ba2 Cu3 O6 , CuO, BaO2 , and Y2 O3 . By compiling the calorimetric and phase equilibria data, a series of Y-Ba-Cu-O isothermal phase diagrams were constructed between 25° and 900°C at 1 atm of oxygen. 相似文献
11.
Oxygen potentials for the coexistence of Cu2 O + Gd2 O3 + CuGd2 O4 , Cu2 O + CuO + CuGd2 O4 , and Cu + Cu2 O + Gd2 O3 three-phase equilibrium have been measured by employing the solid-state galvanic cells
between 960 and 1290 K, respectively. The results obtained in this study indicate that the ternary phase, CuGd2 O4 , is nearly stoichiometric. The measured oxygen potentials for the coexistence of various three-phase assemblages are given by the expressions
between 960 and 1290 K, respectively. Combining the oxygen potentials for the coexistence of Cu2 O + Gd2 O3 + CuGd2 O4 with that of Cu2 O + CuO gives for the reaction
The results obtained in the present investigation suggest that the formation of CuGd2 O4 from component oxides is slightly endothermic and the phase CuGd2 O4 is an entropystabilized compound. The enthalpy and entropy of formation of CuGd2 O4 from component oxides obtained in this study are in excellent agreement with the recent calorimetric data. Phase relations and oxygen-potential diagram for the Cu-Gd-O ternary system have been constructed at 1273 K by combining the results obtained in this study and the auxiliary thermodynamic data available in the literature. 相似文献
between 960 and 1290 K, respectively. The results obtained in this study indicate that the ternary phase, CuGd
between 960 and 1290 K, respectively. Combining the oxygen potentials for the coexistence of Cu
The results obtained in the present investigation suggest that the formation of CuGd
12.
Ho-Yong Lee Chan-Joong Kim Gye-Won Hong 《Journal of the American Ceramic Society》1996,79(11):2912-2916
The formation of spherical pores and regions free of Y2 BaCuO5 (2-1-1) has been studied by melt processing Y1.6 Ba2.3 Cu3.3 O x: in two different atmospheres (air and oxygen). When the sintered Y1.6 Ba2.3 Cu3.3 O x specimens are melted at 1050°C, many spherical pores form in the melted specimens. During the subsequent cooling, the pores are filled by liquid flow and finally solidified to Y2 BaCuO5 -free regions. Melt processing in an oxygen atmosphere produces more pores and regions free of 2-1-1 than in air. Because peritectic melting of YBa2 Cu3 O7-y in an oxygen atmosphere produces more oxygen gas than that in air, the formation of the pores and Y2 BaCuO5 -free regions is suggested to be attributed to the oxygen evolution during the peritectic melting of YBa2 Cu3 O7−y 相似文献
13.
Robert S. Roth Claudia J. Rawn John D. Whitler C. K. Chiang Winnie K. Wong-Ng 《Journal of the American Ceramic Society》1989,72(3):395-399
Studies in the Sr-Y-Cu-O and Ba-Sr-Y-Cu-O systems have revealed that Sr will substitute for Ba in (Ba,Sr)2 YCu3 O6+ x up to about 60%. There are no ternary compounds in the Sr-Y-Cu-O system equivalent to the three ternary phases in the Ba system. A new binary phase, "Sr14 Cu24 O41 "(CuO ∼ 63.158 mol%), was found which forms a solid solution with Y2 O3 to a Sr:Y ratio of approximately 2:1. This phase can also incorporate considerable amounts of Ba and Ca and many other large ions. 相似文献
14.
Jong J. Rha Kyung J. Yoon Suk-Joong L. Kang Duk N. Yoon 《Journal of the American Ceramic Society》1988,71(7):328-C
The rates of forming the superconducting YBa2 Cu3 Ox phase during the calcination of the Y2 O3 , BaCO3 , and CuO powder mixture at 790° and 850°C are considerably enhanced when an inert atmosphere of N2 or He is used instead of O2 . Sintering in an inert atmosphere also produces higher density and larger grain size than in O2 . These results are consistent with the possibility of rapid atomic diffusion in tetragonal YBa2 Cu3 Ox due to either high oxygen vacancy concentration or expanded lattice in an inert atmosphere. 相似文献
15.
Francesca G. Licci Longmei Wang Tullo Besagni 《Journal of the American Ceramic Society》1997,80(7):1821-1830
The reactions of stoichiometric Y2 O3 , CuO, and different barium salts (BaCO3 , Ba(NO3 )2 , BaO2 , BaCuO2 ) for forming various compounds in the yttrium-barium-copper-oxygen system (i.e., YBa2 Cu3 O7–δ , BaCuO2 , Y2 BaCuO5 , and Y2 Cu2 O5 ) were systematically investigated by thermal analysis and X-ray diffractometry. In a few cases, the relevant activation energies were calculated. The reaction pathway and kinetics were significantly dependent on the physicochemical and thermal stability of the barium precursors, as well as on the crystalline size of the reagent. Binary BaO-CuO phases formed at low temperature (650°–700°C) when in the presence of easy-to-decompose barium precursors, and then slowly transformed to ternary compounds; in contrast, when barium ions were released at temperatures of >900°C, ternary phases formed directly from the components. 相似文献
16.
BaCuO2 , Y2 Cu2 O5 , and Y2 BaCuO5 as well as YBa2 Cu3 Ox were synthesized and nonlinear calibration curves for mole fraction versus integrated intensity ratio of X-ray diffraction peaks were obtained for BaCuO2- , Y2 Cu2 O5- , and Y2 BaCuO5- YBa2 Cu3 Ox systems. It is shown that the amount of BaCuO2 contained in orthorhombic YBa2 Cu3 Ox is not negligible, even if the relative intensity of the strongest diffraction peak of BaCuO2 is negligibly weak. 相似文献
17.
W. Y. Ching 《Journal of the American Ceramic Society》1990,73(11):3135-3160
The first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method for electronic structure studies has been applied to a variety of complex inorganic crystals. The theory and the practice of the OLCAO method in the local density approximation are discussed in detail. Recent progress in the study of electronic and optical properties of a large list of ceramic systems are summarized. Eight selected topics on different ceramic crystals focusing on specific points of interest are presented as examples. The materials discussed are AIN, Cu2 O, β-Si3 N4 , Y2 O3 , LiB3 O5 , ferroelectric crystals, Fe-B compounds, and the YBa2 Cu3 O7 superconductor. The results include the band structure, density of states, charge density distribution, spin density distribution, effective charges, total energy and totalenergy-derived results, optical absorption, positron annihilation spectra, and more. Extension of the band theoretical approach to the study of other areas of fundamental ceramic science is also discussed. 相似文献
18.
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
19.
Effect of Ta2 O5 , Nb2 O5 , and HfO2 Alloying on the Transformability of Y2 O3 -Stabilized Tetragonal ZrO2
Dae-Joon Kim 《Journal of the American Ceramic Society》1990,73(1):115-120
The addition of Ta2 O5 , Nb2 O5 , and HfO2 enhanced the transformability of Y2 O3 -stabilized tetragonal ZrO2 polycrystal (Y-TZP), which was indicated by an increase in phase transformation temperatures and fracture toughness of Y-TZP. Comparison of the alloying effects of these oxides on the transformability and crystal structure of Y-TZP suggested that an alloying oxide which increases the c/a axial ratio (tetragonality) of TZP also increases the transformability. Empirical equations to predict the tetragonality are proposed. Calculated tetragonalities showed good agreement with measured values in the systems ZrO2 -Y2 O3 -Ta2 O5 , -Nb2 O5 , and -HfO2 . 相似文献
20.
A Simple Way to Synthesize Yttrium Aluminum Garnet by Dissolving Yttria Powder in Alumina Sol 总被引:4,自引:0,他引:4
Kyoung R. Han Hee Jin Koo Chang Sup Lim 《Journal of the American Ceramic Society》1999,82(6):1598-1600
A precursor for Y3 Al5 O12 was synthesized as a YAG sol by simply dissolving Y2 O3 powder in an alumina sol. Phase-pure Y3 Al5 O12 powder was obtained by precipitating the YAG sol with an aqueous dilute ammonia solution followed by calcination at 1100°C. TG/DTA analysis showed an exotherm at 938°C attributed to formation of YAG phase and weight loss of 44% at 1000°C. XRD and FT-IR analysis showed that phase-pure YAG can be formed through noncrystalline and metastable hexagonal YAlO3 without forming either yttrium or aluminum formate intermediate. 相似文献