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1.
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
2.
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
3.
The influence of Nd2 O3 doping on the reaction process and sintering behavior of BaCeO3 is investigated. Formation of BaCeO3 is initiated at 800°C and completed at 1000°C. When Nd2 O3 is added to the starting materials, the formation of BaCe1–x Ndx O3–δ is delayed and the temperature for complete reaction is increased to 1100°C. Only a BaCe1-x Ndx O3–δ solid solution with an orthorhombic crystal structure is present in the specimens for x ≤ 0.1. A secondary phase rich in Ce and Nd is formed within grains and at grain boundaries, when the Nd2 O3 content is greater than the solubility limit (x ≥ 0.2). Pure BaCeO3 is difficult to sinter, even at 1500°C, and only a porous microstructure could be obtained. However, doping BaCeO3 with Nd2 O3 markedly enhances its sinterability. The enhancement of the sinterability of Nd2 O3 -doped specimens at x ≤ 0.1 is attributed to the increase in the concentration of oxygen ion vacancies, which increases the diffusion rate. At x ≥ 0.2, the grain size is abnormally coarsened, which is caused by the formation of a liquid phase. While this liquid phase accelerates sintering, its beneficial effect on densification is counteracted by the segregation of the secondary grain-boundary phase which inhibits sintering. 相似文献
4.
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
5.
Karen M. Cruickshank Xiping Jing Graeme Wood Eric E. Lachowski Anthony R. West 《Journal of the American Ceramic Society》1996,79(6):1605-1610
A solid-solution phase with the general formula Ba6-3x Nd8+2x Ti18 O54 , where 0.25(5) ≤×≤ 0.75(5), has been characterized at 1250°C; this phase has been variously described as BaNd2 Ti4 O12 and BaNd2 Ti5 O14 in the literature. Variation in its stoichiometry is accommodated via the cation substitution mechanism, 3Ba2 ⇆2Nd3+ . The location and extent of the solid solution were demonstrated by a combination of phase diagram studies and X-ray diffraction techniques, including lattice parameter measurements and electron microscopy. A combination of techniques was employed due to the insensitivity of secondary phase detection by X-ray diffraction in this system. Using this approach, a second possible solid-solution mechanism, Ba2+ 2Nd3+ ⇆2Ti4+ , is discounted. 相似文献
6.
Yangyang Ji Jingkui Liang Zhan Chen Sishen Xie 《Journal of the American Ceramic Society》1991,74(2):444-446
The phase relations at a temperature below "subsolidus" in the system Al2 O3 –B2 O3 –Nd2 O3 are reported. Specimens were prepared from various compositions of Al2 O3 , B2 O3 , and Nd2 O3 of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100°C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl3 (BO3 )4 (NAB), has a phase transition at 950°C ± 15°C. The high-temperature form of NAB has a second harmonic generation (SHG) efficiency of KH2 PO4 (KDP) of the order of magnitude of the form which has been used as a good self-activated laser material, and the low-temperature form of NAB has no SHG efficiency. 相似文献
7.
Shuigen Huang Omer Van der Biest Jef Vleugels Lin Li 《Journal of the American Ceramic Society》2006,89(8):2596-2601
The phase relations in the Nd2 O3 –Y2 O3 system were experimentally studied in the 1300°–1600°C range. X-ray diffraction, scanning electron microscopy, and electron probe microanalysis were applied to analyze the phase composition of annealed Nd2 O3 –Y2 O3 mixtures with varying Y2 O3 content. A thermodynamic assessment was conducted using the experimental data obtained. The excess Gibbs energies of the solution phases were described based on a simple substitutional solution model. A consistent set of optimized interaction parameters was derived for the Gibbs energy of the constituent phases, resulting in a good match between calculated and experimental data. 相似文献
8.
Robert S. Roth Nong M. Hwang Claudia J. Rawn Benjamin P. Burton Joseph J. Ritter 《Journal of the American Ceramic Society》1991,74(9):2148-2151
New data are presented on the phase equilibria of the binary systems CaO-CuO and CaO-Bi2 O3 . Corrected compositions are reported for Ca.Bi6 O13 and Ca2 Bi2 O5 and a new metastable high-temperature phase is reported for a composition near Ca6 Bi7 O16.5 . The composition and decomposition temperatures for Ca1–x .CuO2 are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively. 相似文献
9.
Yoshihiro Kusano Takeyuki Kikuchi Jun Takada Minoru Fukuhara Yasunori Ikeda Zenji Hiroi 《Journal of the American Ceramic Society》1999,82(5):1329-1332
The phase diagram of the BaO(BaCO3 )-CaO-CuO system, especially in the barium-rich region at 900°C in air, was studied. Two new different oxycarbonates were observed: Ba8 Ca16/15 Cu64/15 O11.20 (CO3 )2.66 and a solid-solution series with a chemical composition of Ba2 Ca x + y Cu1+( x /2)- y O2+delta (CO3 )1- z (where 0 ≤ to x ≤ to 2/39 and 0 ≤ to y ≤ to 16 x /5). The oxycarbonate solid solution was formed in a region of the compositional triangle Ba:Ca:Cu (in moles) = (2:0:1)-(39:1:20)-(65:7:28). The solid-solution structure had P 4/ mmm symmetry, with lattice parameters a similar/congruent a p and c similar/congruent 2 a p , where a p represents the perovskite cell. The Ba8 Ca16/15 Cu64/15 O11.20 (CO3 )2.66 compound, which had Pm 3 m symmetry with a lattice parameter a = 0.8116(2) nm, had no chemical-solubility range. 相似文献
10.
Girish Harshé Dinesh Agrawal Santosh Limaye 《Journal of the American Ceramic Society》1994,77(7):1965-1968
The NaZr2 P3 O12 (NZP) family of materials is attracting increasing attention due to its low-thermal-expansion behavior. The system Ba1+x Zr4 P6–2x Si2x O24 (0 ≤ x ≤ 1), belonging to the NZP family, shows ultralow thermal expansion over a wide temperature range. It also shows anisotropy in its lattice thermal expansion. This causes microcracking as the sintered specimens are cooled, which results in degradation of the mechanical properties. In this work, the chemical stability, strength, and Young's modulus of Ba1+x Zr4 P6–2x O24 ( X = 0.25 and 0.5) ceramics at high temperatures have been determined. An attempt has been made to correlate the mechanical properties to the thermal expansion anisotropy. 相似文献
11.
The thermodynamic data for the YO1.5 –BaO, BaO-CuOx , and YO1.5 –CuOx quasi-binary systems were optimized from experimental phase diagrams. They were used to calculate tentative phase diagrams for the YO1.5 –BaO—CuOx quasi-ternary system. The equilibrim liquidus surface and the isothermal sections of the ternary system at 900°, 925°, 950°, 975°, and 1000°C were calculated. The isopleths containing YBa2 Cu3 O7-δ were also calculated. 相似文献
12.
The dependence of the degree of nonstoichiometry of YBa2 Cu3 07–x (123) on temperature and oxygen pressure has been determined by thermogravimetric analysis (TGA) in the temperature range 400° to 950°C and the oxygen pressure range 10–6 to 1 atm (1 atm = 105 Pa). The nature of the decomposition of 123 in the temperature range 750° to 950°C and the oxygen pressure range 10–6 to 10–2 atm has been determined by TGA and X-ray diffractometry (XRD). As the oxygen pressure decreases, the decomposition of 123 follows the sequence 123→ Y2 BaCuo5 (211) + BaCuO2 ° Cu2 O→ 211 ° BaCuO2 ° BaCu2 O2 → 211 ° YBa3 Cu2 Ox (132) ° BaCu2 O2 → 211 ° BaCu2 O2 °BaO. The incongruent melting temperatures have been determined in the oxygen pressure range 10–6 to 1 atm by differential thermal analysis, and the phases formed on solidification have been identified by XRD. The stability diagram for the composition 123 has been constructed. 相似文献
13.
In the synthesis of the superconducting compound Ba2 YCu3 O7-x from a stoichiometric mixture containing BaCO3 , Y2 O3 , and CuO In air, a low-melting liquid phase is formed at about 890°C. The liquid phase was identified as a ternary eutectic located within the compatibility triangle Ba2 YCu3 O7-x –BaCuO2 –CuO. The implication of this finding for the processing of Ba2 YCu3 O7-x is discussed. 相似文献
14.
Lijie Zhang Jie Chen Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1989,72(10):1997-2000
In situ annealing studies of YBa2 Cu3 O6+x performed in an optical hot stage revealed that, at temperatures ∧450°, localized melting occurred. On subsequent cooling, a discrete second phase was observed at the YBa2 Cu3 O6+x grain boundaries. Quantitative chemical analysis using X-ray wavelength dispersive spectroscopy indicated that the second phase was composed of a barium oxycarbonate. The source of the carbon in the second phase was identified to be CO2 in the atmosphere. 相似文献
15.
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
16.
Subsolidus phase relationships in the Ga2 O3 –In2 O3 –SnO2 system were studied by X-ray diffraction over the temperature range 1250–1400°C. At 1250°C, several phases are stable in the ternary system, including Ga2 O3 ( ss ), In2 O3 ( ss ), SnO2 , Ga3− x In5+ x Sn2 O16 , and several intergrowth phases that can be expressed as Ga4−4 x In4 x Sn n −4 O2 n −2 where n is an integer. An In2 O3 –SnO2 phase and Ga4 SnO8 form at 1375°C but are not stable at 1250°C. GaInO3 did not form over the temperature range 1000–1400°C. 相似文献
17.
pela Kunej Sreo D. kapin Danilo Suvorov 《Journal of the American Ceramic Society》2009,92(10):2373-2377
In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi2 O3 −TiO2 −Nd2 O3 system at 1100°C. The samples were analyzed using X-ray powder diffraction and scanning electron microscopy with energy- and wavelength-dispersive spectroscopy. A single-phase pyrochlore ceramic was obtained with the addition of 4.5 mol% of Nd2 O3 . We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi(1.6–1.08 x ) Nd x Ti2 O(6.4+0.3 x ) , where 0.25< x <0.96; (ii) the solid solution Bi4− x Nd x Ti3 O12 , where 0< x <2.6; and (iii) the Nd2− x Bi x Ti2 O7 solid solution, where 0< x <0.35. The determined phase relations in the pyrochlore-rich part are presented in a partial phase diagram of the Bi2 O3 −TiO2 −Nd2 O3 system in air at 1100°C. 相似文献
18.
Stefanie Kaesche Peter Majewski Fritz Aldinger 《Journal of the American Ceramic Society》1999,82(1):197-202
Phase equilibria of the quasi-quaternary system BiO1.5 –SrO-YO1.5 –CuO have been studied at a temperature of 950°C in air, with special regard to the 1212 phase. The 1212 phase reveals only very small changes in the cation ratio. Single-phase samples exist for (Bi0.24–0.36 Cu0.42-0.55 )–Sr2 Y1.27 Cu2 O y compositions. The bismuth-rich composition of the 1212 phase is in thermodynamic equilibrium with a liquid and the 2212 phase, whereas the copper-rich composition is in equilibrium with five other phases. The influence of combined calcium and lead doping also has been studied. Exceeding the calcium saturation of the 1212 phase increases the amount of 2212 as a secondary phase. Single-phase 1212 samples do not show any superconductivity in either the as-prepared or the post-annealed state. The only compositions with bulk superconductivity are those with calcium and lead doping after annealing at a temperature of 980°C. The superconductivity is attributed to the 2212 phase crystallizing from the melt during slow cooling. 相似文献
19.
Asha Mary John Rajan Jose Jose Kurian Poo Koodan Sajith Jacob Koshy 《Journal of the American Ceramic Society》1999,82(6):1421-1424
A new group of complex perovskites Ba2 REHfO5.5 (where RE = La, Pr, Nd, and Eu) has been synthesized and sintered as single-phase materials with high sintered density and stability using a solid-state reaction method for the first time. The structure of Ba2 REHfO5.5 has been studied by X-ray diffactometry (XRD) and all of the perovskites are isostructural and have a cubic structure. The dielectric constant and loss factor values of these materials are in a range suitable for their use as substrates for YBa2 Cu3 O7-delta superconductors. XRD and resistivity measurements show that there is no detectable reaction between YBa2 Cu3 O7-delta and Ba2 REHfO5.5 , even when the two substances are mixed thoroughly and sintered at 950°C for 15 h. The addition of Ba2 REHfO5.5 up to 20 vol% in YBa2 Cu3 O7-delta -Ba2 REHfO5.5 composite shows no detrimental effect on the superconducting transition temperature of YBa2 Cu3 O7-delta . Thick films of YBa2 Cu3 O7-delta fabricated on polycrystalline Ba2 REHfO5.5 substrate have a superconducting zero resistivity transition of 92 K, indicating the suitability of these new materials as substrates for YBa2 Cu3 O7-delta films. 相似文献
20.
Thommy Ekström Harald Herbertsson Matthew James Ian Fleck 《Journal of the American Ceramic Society》1994,77(12):3087-3092
β-sialon and Nd2 O3 -doped α-sialon materials of varying composition were prepared by sintering at 1775° and 1825°C and by glass-encapsulated hot isostatic pressing at 1700°C. Composites were also prepared by adding 2–20 wt% ZrO2 (3 mol% Nd2 O3 ) or 2–20 wt% ZrN to the β-sialon and α-sialon matrix, respectively. Neodymium was found to be a fairly poor α-sialon stabilizer even within the α-phase solid solution area, and addition of ZrN further inhibited the formation of the α-sialon phase. A decrease in Vickers hardness and an increase in toughness with increasing content of ZrO2 (Nd2 O3 ) or ZrN were seen in both the HIPed β-sialon/ZrO2 (Nd2 O3 ) composites and the HIPed Nd2 O3 -stabiIized α-sialons with ZrN additions. 相似文献