共查询到20条相似文献,搜索用时 46 毫秒
1.
Yasuro Ikuma Eriko Shimada Nobuko Okamura 《Journal of the American Ceramic Society》2005,88(2):419-423
An extensive X-ray study of CeO2 –Nd2 O3 solid solutions was performed, and the densities of solid solutions containing various concentrations of NdO1.5 were measured using several techniques. Solid solutions containing 0–80 mol% NdO1.5 were synthesized by coprecipitation from Ce(NO3 )3 and Nd(NO3 )3 aqueous solutions, and the coprecipitated samples were sintered at 1400°C. A fluorite structure was observed for CeO2 –NdO1.5 solid solutions with 0–40 mol% NdO1.5 , which changed to a rare earth C-type structure at 45–75 mol% NdO1.5 . The change in the lattice parameters of CeO2 –NdO1.5 solid solutions, when plotted with respect to the NdO1.5 concentration, showed that the lattice parameters followed Vegard's law in both the fluorite and rare earth C-type regions. The maximum solubility limit for NdO1.5 in CeO2 solid solution was approximately 75 mol%. The relationship between the density and the Nd concentration indicated that the defect structure followed the anion vacancy model over the entire range (0–70 mol% NdO1.5 ) of solid solution. 相似文献
2.
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
3.
Makoto Kambara Takateru Umeda Minoru Tagami Xin Yao Eugene A. Goodilin Yuh Shiohara 《Journal of the American Ceramic Society》1998,81(8):2116-2124
Quasi-ternary phase diagrams of the NdO1.5 -BaO-CuO x system near the CuO x corner have been constructed near the peritectic temperature in air of the Nd1+ x Ba2− x Cu3 O6+delta (Nd123) solid-solution phase. Liquidus curves were determined by measuring the temperature dependences of the neodymium, barium, and copper solubilities in Nd-Ba-Cu-O solutions with different BaO:CuO ratios. Solidus line compositions and equilibrium tie lines were determined by analyzing the compositions of the Nd123 solid solution equilibrated with the melt by quenching samples held isothermally. Based on the tie-line features in the Nd123-and- liquid two-phase field, the Nd123 solid solution with the smaller substitution content was observed to be equilibrated with the solution melt with a higher BaO:CuO ratio, even in an air atmosphere. Nd123 crystal with a substitution content of ∼0.02 could be formed from the solution with the BaO:CuO ratio of greaterthan equal to0.75, which resulted in higher critical superconducting transition temperatures. 相似文献
4.
EIJI TANI MASAHIRO YOSHIMURA SHIGEYUKI SOMIYA 《Journal of the American Ceramic Society》1983,66(7):506-510
The phase diagram of the system ZrO2 -CeO2 was rein-vestigated using hydrothermal techniques. Cubic, tetragonal, and monoclinic solid solutions are present in this system. The tetragonal solid solution decomposes to monoclinic and cubic solid solutions by a eutectoid reaction at 1050°50°C. The solubility limits of the tetragonal and cubic solid solutions are about 18 and 70 mol% CeO2 , respectively, at 1400°C, and about 16 and 80 mol% CeO2 , respectively, at 1200°C. Solubility limits of the monoclinic and cubic solid solutions are about 1.5 and 88 mol% CeO2 at 1000°C, and 1.5 and 98 mol% CeO2 at 800°C, respectively. The compound Ce2 Zr3 O10 is not found in this system. 相似文献
5.
Yttria-ceria-doped tetragonal zirconia (Y,Ce)-TZP)/alumina (Al2 O3 ) composites were fabricated by hot isostatic pressing at 1400° to 1450°C and 196 MPa in an Ar–O2 atmosphere using the fine powders prepared by hydrolysis of ZrOCl2 solution. The composites consisting of 25 wt% Al2 O3 and tetragonal zirconia with compositions 4 mol% YO1.5 –4 mol% CeO2 –ZrO2 and 2.5 mol% YO1.5 –5.5 mol% CeO2 –ZrO2 exhibited mean fracture strength as high as 2000 MPa and were resistant to phase transformation under saturated water vapor pressure at 180°C (1 MPa). Postsintering hot isostatic pressing of (4Y, 4Ce)-TZP/Al2 O3 and (2.5Y, 5.5Ce)-TZP/Al2 O3 composites was useful to enhance the phase stability under hydrothermal conditions and strength. 相似文献
6.
Masatomo Yashima Hiroyuki Takashina Masato Kakihana Masahiro Yoshimura 《Journal of the American Ceramic Society》1994,77(7):1869-1874
Low-temperature phase equilibria ranging from 1000° to 1200°C in the ZrO2 –CeO2 system were investigated by annealing compositionally homogeneous ZrO2 –CeO2 solid solutions in a Na2 B2 O7 .1 NaF flux. The 5 mol% CeO2 samples decomposed into monoclinic ( m ) and tetragonal ( t ) phases during annealing at 1100°2 and 1120°C, and the t -phase transformed diffusionlessly into monoclinic ( m ') symmetry during quenching. A eutectoid reaction, t → ( m + c ), was confirmed to occur at 1055°± 10°C, where the equilibrium compositions of the t -, m -, and c -phases were 11.2 ± 2.8, 0.9 ± 0.9, and 84 ± 1 mol% CeO2 , respectively. The equilibrium phase boundaries were almost independent of the annealing time and/or the flux:sample ratio, which indicates that the flux accelerates the reaction rate withouts affecting the equilibration. The previous data are discussed using metastable–stable phase diagrams. The discrepancies of the low-temperature phase diagram in the literature are attributable to either regarding the metastable phase boundaries as stable ones or ignoring the sluggish kinetics. 相似文献
7.
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
8.
The oxygen storage capacity (OSC) of CeO2 –ZrO2 solid solutions that were directly formed as nanocrystals by thermal hydrolysis of acidic aqueous solutions of (NH4 )2 Ce(NO3 )6 and ZrOCl2 at 150°C increased from 94 μmol of O2 /g for pure CeO2 to >400 μmol of O2 /g for compositions of CeO2 /ZrO2 with molar ratios (C/Z) from 74.1/25.9 to 41.7/58.3 (maximum value of 431 μmol O2 /g was reached at the composition C/Z = 51.7/48.3) and then decreased with increased ZrO2 content in the solid solutions. As compared with pure CeO2 , the CeO2 –ZrO2 solid solutions that contained <84.8 mol% ZrO2 maintained high specific surface area and large pore volume with nanosized pores (pore size at maximum pore volume) <10 nm in diameter after heat treatment at 700°C. 相似文献
9.
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
10.
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
11.
Petra A. Langjahr Rainer Oberacker Michael J. Hoffmann 《Journal of the American Ceramic Society》2001,84(6):1301-1308
Investigations of changes in phase composition, mechanical properties, and microstructure of ZrO2 -based plasma-sprayed thermal barrier coatings (TBCs) with 8 mol% CeO2 , 19.5 mol% CeO2 /1.5 mol% Y2 O3 , 35 mol% CeO2 , and 4.5 mol% Y2 O3 after long-term heat treatments at typical operation temperatures (1000°–1400°C) are presented. Experimental studies include X-ray diffractometry, mechanical testing, and scanning electron microscopy. Thermal cycling experiments also have been performed. TBCs with 8 mol% CeO2 contain mainly the tetragonal equilibrium phase and, therefore, show rapid failure because of the high amount of tetragonal → monoclinic phase transformation, even after relatively short heat treatments (1250°C/1 h). In the case of the other systems that consist mainly of the tetragonal or cubic nonequilibrium phases, TBCs with 19.5 mol% CeO2 /1.5 mol% Y2 O3 or 35 mol% CeO2 reveal a smaller amount of monoclinic phase after long-term heat treatments (1250°C/1000 h) compared with TBCs containing 4.5 mol% Y2 O3 . TBCs containing 35 mol% CeO2 show a higher degree of sintering than the TBCs with 19.5 mol% CeO2 /1.5 mol% Y2 O3 and, therefore, a greater increase of the elastic modulus. Among the systems investigated, TBCs containing 4.5 mol% Y2 O3 exhibit the highest resistance to failure in thermal-cycling experiments. 相似文献
12.
Daniel R. Kammler Bryan J. Harder Nikolas W. Hrabe Nikkia M. McDonald Gabriela B. González David A. Penake Thomas O. Mason 《Journal of the American Ceramic Society》2002,85(9):2345-2352
Subsolidus phase relations have been determined in the CdO–InO1.5 –SnO2 system at 1175°C. A cubic-bixbyite solution In2−2 x (Cd,Sn)2 x O3 (0 < x < 0.34), a cubic spinel solution (1− x )CdIn2 O4 – x Cd2 SnO4 (0 < x < 0.75), and an orthorhombic-perovskite solution Cd1− x Sn1− x In2 x O3 (0 < x < 0.045) having the GdFeO3 structure have been discovered. The CdO phase field exists over a small range of InO1.5 (<3%) and SnO2 (<1%). Orthorhombic Cd2 SnO4 (Sr2 PbO4 structure) and rutile SnO2 appear to be point compounds with negligible solubility. The vertical section between spinel CdIn2 O4 and orthorhombic Cd2 SnO4 was determined between 900° and 1175°C. The spinel phase field (1− x )CdIn2 O4 – x Cd2 SnO4 was found to extend between x = 0 and x = 0.75 at 1175°C or x = 0.78 at 900°C. All of the phases in this system appear to allow small excess quantities of the donors In and/or Sn (vs cation stoichiometry) which may be the source of the electrons that give these oxides their n-type character. The electrical and optical properties of bulk and thin-film specimens in this system are compared and contrasted with each other and the relative merits of each are assessed. 相似文献
13.
Toshiyuki Mori Hiroshi Yamamura Syoshichi Saito 《Journal of the American Ceramic Society》1996,79(12):3309-3312
The ionic conductivity of the ceria-samaria (CeO2 -Sm2 O3 ) system is higher than that of yttria-stabilized zirconia and other CeO2 -based oxides. In this study, a small amount of alkali-element-doped CeO2 -Sm2 O3 solid solution was prepared. This solid solution was characterized by measuring the powder density and the chemical composition. Moreover, its electrochemical properties were investigated in the temperature range from 700° to 1000°C. It was found that a small amount of alkali-element-doped CeO2 solid solution enhanced the ionic conductivity. The power density of an oxygen-hydrogen fuel cell for alkali-element-doped CeO2 -Sm2 O3 ceramics exhibited high values at low temperatures such as 700° to 800°C. It is concluded that the improved fuel cell performance can be attributed to the high stability of this composition in the fuel atmosphere. 相似文献
14.
Geoffrey A. Tompsett Nigel M. Sammes Osamu Yamamoto 《Journal of the American Ceramic Society》1997,80(12):3181-3186
Ceramic samples of Ce1− x Gd x O2− y and yttria-stabilized zirconia (YSZ) were prepared using solid-state methods. Polished faces of disks of these materials were held in intimate contact in a reaction cell at temperatures ranging from 1000° to 1300°C for durations up to 72 h. XRD, SEM, and microprobe Raman techniques were used to analyze the resulting reactions and ion diffusion. No reaction was observed at 1000°C after 72 h between the 10-mol%- and 20-mol%-Gd-doped CeO2 and the YSZ. However, at 1300°C, a mixing region 25 μ m wide occurred, resulting in a cubic phase, where Zr4+ ions diffused into the CeO2 . 相似文献
15.
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
16.
The effect of rare-earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N2 at 1800° to 2000°C was studied. When a single-component oxide, such as CeO2 , Nd2 O3 , La2 O3 , Sm2 O3 , or Y2 O3 , was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y2 O3 –Ln2 O3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare-earth oxides is discussed in relation to the additive compositions. 相似文献
17.
Two cubic pyrochlore phases exist in the system ZnO–Bi2 O3 –Sb2 O5 . Neither has the supposed "ideal" stoichiometry, Zn2 Bi3 Sb3 O14 . One, P 1 , is a solid solution phase, Zn2+ x Bi2.96−( x − y ) Sb3.04− y O14.04+δ where 0< x <0.13(1), 0< y <0.017(2) and a =10.4285(9)−10.451(1) Å. The other, P 2 , is a line phase, Zn2 Bi3.08 Sb2.92 O13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P 1 and P 2 in the ZnO–Bi2 O3 –Sb2 O5 phase diagram have been determined. 相似文献
18.
Tsugio Sato Kenji Dosaka Toshiaki Yoshioka Akitsugu Okuwaki Kazuo Torii Yoshiro Onodera 《Journal of the American Ceramic Society》1992,75(3):552-556
Amorphous CeO2 –ZrO2 gels were prepared by coprecipitation in ammonia solutions. The onset of crystallization of the gels, from calcining in air, was 420°C, while 200° to 250°C in the presence of water and organic solvents such as methanol and ethanol. The sintering behaviors of CeO2 –ZrO2 powders were sensitive to the crystallizing conditions, since hard agglomerates formed when the precipitated gels were crystallized by normal calcination in air, whereas soft agglomerates formed when they were crystallized in water or organic solvents. CeO2 –ZrO2 powders crystallized in methanol and water at 250°C were sintered to full theoretical density at 1150° and 1400°C, respectively, whereas that crystallized by calcination in air at 450°C was sintered to only 95.2% of theoretical density, even at 1500°C. 相似文献
19.
Yoshio Sakka Yasumichi Oishi Ken Ando Shoji Morita 《Journal of the American Ceramic Society》1991,74(10):2610-2614
Zr–Hf interdiffusions were carried out at 1350° to 1520°C for polycrystalline tetragonal solid solutions of 14CeO2 ·86(Zr1- x Hf x )O2 with X = 0.02 and 0.10. Lattice and grain-boundary interdiffusion parameters were calculated from the concentration distributions by using Oishi and Ichimura's equation. Lattice interdiffusion coefficients were described by D = 3.0 × 103 exp[-623 (kJ/mol)/ RT ] cm2 /s and grain-boundary interdiffusion parameters by δ D ' = 0.29 exp[-506 (kJ/mol)/ RT ] cm3 /s. The cation diffusivity was lower than the anion diffusivity. The results were compared with diffusivities in the fluorite-cubic solid solution. The critical grain radii for stabilization of the tetragonal phase in CeO2 -doped ZrO2 were 11 and 6 μm for the solutions with 2 and 10 mol% HfO2 substitution, respectively, both of which are much greater than in the Y2 O3 -doped ZrO2 solid solution. 相似文献
20.
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