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1.
Danjela Kuer Darko Hanel Janez Holc Marko Hrovat Drago Kolar 《Journal of the American Ceramic Society》2001,84(5):1148-1154
La1− y Sr y Fe1− x Al x O3−δ perovskites were studied as potential materials for solid-oxide fuel cell (SOFC) cathodes. The phase relations in the LaFeO3 –SrFeO3−δ –LaAlO3 system were investigated by X-ray powder diffraction analysis. The defect structure of the La1− y Sr y Fe1− x Al x O3−δ perovskites was investigated by Mössbauer spectroscopy and weight-loss analysis. Relations between the nonstoichiometry and the conductivity of the La1− y Sr y Fe1− x Al x O3−δ perovskites were investigated. The incorporation of aluminum ( x ) into LaFe1− x Alx O3 was found to have no influence on the defect structure but to decrease the conductivity. The incorporation of strontium ( y ) into La1− y Sr y Fe1− x Al x O3−δ promotes the formation of anion vacancies and Fe4+ that lead to higher conductivity. 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.
Near-field scanning microwave microscopy was applied to investigate the dielectric properties and microstructure in a polycrystalline LaAlO3 –TiO2 diffusion couple, which included three regions containing different phases and microstructures. Relatively low (La2 Ti4 Al18 O38 ), high (α-La2/3 TiO3 ), and intermediate (La4 Ti9 O24 ) dielectric constant phases were distinguished at the inter-diffusion interface in optical, backscattered electron scanning electron microscopy, and scanning microwave microscopy (SMM) images. The relative ranking of dielectric constants based on SMM examination was as follows: TiO2 >α-La2/3 TiO3 >La4 Ti9 O24 >LaAlO3 >La2 Ti4 Al18 O38 . La2/3 TiO3 and LaAlO3 will form solid solutions in the LaAlO3 -rich region. The reaction paths leading to phase development are discussed. 相似文献
4.
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
5.
Subsolidus phase relations in the La2 O3 –BaO–CuO system were studied at 950°C. Three previously reported binary compounds exist (La2 CuO4 , BaLa2 O4 , and BaCuO2 ) and five previously reported ternary phases occur (La2-x Bax CuO4-(x/2)+δ , La4-2x Ba2+2x Cu2-x O10-2x , La2-x Ba1+x Cu2 O6-(x-2) , La3-x Ba3+x Cu6 O14±δ , and La4 BaCu5 O13+δ ). Of the seven phases in the diagram, all but BaLa2 O4 , BaCuO2 , and La4 BaCu5 O13+δ were shown to exhibit significant ranges of solubility. The diagram is important in that both >30 K (La2-x Bax CuO4-(x/2)+δ ) and >90 K (La3-x Ba3+x Cu6 O14+δ , x=1) superconductors occur. 相似文献
6.
Santanu Basu Amitava Chakraborty Parukuttyamma Sujatha Devi Himadri Sekhar Maiti 《Journal of the American Ceramic Society》2005,88(8):2110-2113
Nanocrystalline La0.9 Sr0.1 Al0.85 Co0.05 Mg0.1 O3 oxide powder was synthesized by a citrate–nitrate auto-ignition process and characterized by thermal analysis, X-ray diffraction, and impedance spectroscopy measurements. Nanocrystalline (50–100 nm) powder with perovskite structure could be produced at 900°C by this process. The powder could be sintered to a density more than 96% of the theoretical density at 1550°C. Impedance measurements on the sintered samples unequivocally established the potential of this process in developing nanostructured lanthanum aluminate-based oxides. The sintered La0.9 Sr0.1 Al0.85 Co0.05 Mg0.1 O3 sample exhibited a conductivity of 2.40 × 10−2 S/cm in air at 1000°C compared with 4.9 × 10−3 S/cm exhibited by La0.9 Sr0.1 Al0.85 Mg0.15 O3 . 相似文献
7.
Masashi Mori Yoshiko Hiei Tohru Yamamoto 《Journal of the American Ceramic Society》2001,84(4):781-786
The thermal expansion of La0.9 Sr0.1 Cr1- x M x O3 (M = Mg, Al, Ti, Mn, Fe, Co, Ni; 0 ≤ x ≤ 0.1) perovskites has been studied in oxidizing and reducing atmospheres in the temperature range from 50° to 1000°C. Cobalt doping of La0.9 Sr0.1 CrO3 was an effective way of increasing the average linear thermal expansion coefficient (TEC), whereas titanium doping showed a negative effect. No effect on the TECs was observed for the B-site dopants in perovskites with the remaining dopants. Linear thermal expansion behavior was observed in the La0.9 Sr0.1 Cr1- x M x O3 perovskites with doping of ≥1 mol% aluminum or 10 mol% cobalt. TECs of La0.9 Sr0.1 Cr0.96 Co0.02 Al0.02 O3 were 10.5 × 10− 6 /°C in air, 10.7 × 10−6 /°C under He–H2 atmosphere (oxygen partial pressure of 4 × 10− 15 atm at 1000°C), and 11.8 × 10− 6 /°C in H2 atmosphere. 相似文献
8.
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
9.
Reactions between Strontium-Substituted Lanthanum Manganite and Yttria-Stabilized Zirconia: II, Diffusion Couples 总被引:1,自引:0,他引:1
Kjersti Kleveland Mari-Ann Einarsrud Christian R. Schmidt Senem Shamsili Sonia Faaland Kjell Wiik Tor Grande 《Journal of the American Ceramic Society》1999,82(3):729-734
Formation of secondary phases and diffusion of cations in diffusion couples of yttria-stabilized zirconia and lanthanum manganite substituted with 0 to 60 mol% strontium have been studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Only the primary phases were observed after 120 h at 1200°C, while formation of secondary phases was identified already after 1 h heat treatment at 1350°C. The phase composition of the reaction layer altered from La2 Zr2 O7 to SrZrO3 at increasing Sr content in La x Sr1- x MnO3 . The thickness of the reaction layer was increasing with heat treatment time. In diffusion couples of La0.4 Sr0.6 MnO3 formation of manganese oxide was observed in the perovskite layer after 1 h heat treatment at 1350°C, while isolated grains of SrZrO3 relatively deep inside the zirconia were observed after longer heat treatment time. Diffusion of Mn into zirconia was observed preferenced along grain boundaries in the early stage of the interface reaction. 相似文献
10.
Synthesis and Preparation of Lanthanum Aluminate Target for Radio-Frequency Magnetron Sputtering 总被引:1,自引:0,他引:1
Gun Yong Sung Kwang Yong Kang Sin-Chong Park 《Journal of the American Ceramic Society》1991,74(2):437-439
A polycrystalline LaAlO3 target for the radio-frequency (rf) magnetron sputterings of LaAlO3 thin films has been prepared. These films serve as a buffer layer for high- T c YBa2 Cu3 O7– x superconducting thin films on Si. Synthesis of lanthanum aluminate powder from a mixture of La2 O3 and Al2 O3 powders was performed by calcining from 1000° to 1600°C in air. Characterization of the calcined powders by X-ray diffraction indicates that full development of LaAlO3 phase was evident in the sample calcined for 3 h at 1600°C in air. A polycrystalline LaAlO3 target was prepared by heat treatment at 1500°C for 2 h in air after pressureless sintering at 1750°C for 3 h in Ar. Thin films of the LaAlO3 on Si (100) were obtained by rf magnetron sputtering using the target and oxygen-annealing the as-deposited films. 相似文献
11.
The ternary phase diagram of Al2 O3 -La2 O3 -TiO2 at 1400°C was determined with 12 compatibility triangles. Al2 O3 stabilizes the A-site-deficient La2/3 TiO3 perovskite structure. According to XRD and microstructural investigations, the solid solution extends along the La2/3 TiO3 -LaAlO3 tie line from at least 4 mol% LaAlO3 to pure LaAlO3 . With increasing LaAlO3 content, the stabilized La2/3 TiO3 structure changes from orthorombic via tetragonal to cubic. 相似文献
12.
Keqin Huang Robin S. Tichy John B. Goodenough 《Journal of the American Ceramic Society》1998,81(10):2576-2580
Alternating current impedance spectroscopy and electron microscopy were used to investigate the effect of grain boundaries in LSGM-based materials. The impurity LaSrGa3 O7 existing in the samples La0.8 Sr0.2 Ga1- y Mg y -O3–0.5(0.2+ y ) ( y = 0.05–0.10) gives a contribution to a perfect or depressed grain-boundary semicircle in the impedance spectroscopy. The depressed semicircle represents a constant phase element (CPE) indicating LaSrGa3 O7 is an oxide-ion insulator. The grain-boundary semicircle vanishes if a hydrogen-containing atmosphere is applied. This fact may reflect proton conduction in LaSrGa3 O7 . In contrast, the impurity LaSrGaO4 existing, for example, in the samples x = 0.20, y = 0.25–0.30 gives no grain-boundary contribution to the impedance. 相似文献
13.
Subsolidus phase relationships in the Ga2 O3 –Al2 O3 –TiO2 system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO2 (rutile), Ga2−2 x Al2 x O3 ( x ≤0.78 β-gallia structure), Al2−2 y Ga2 y O3 ( y ≤0.12 corundum structure), Ga2−2 x Al2 x TiO5 (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga4−4 x Al4 x Ti n −4 O2 n −2 ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work. 相似文献
14.
Hwack Joo Lee Hyun Min Park Yang Koo Cho Sahn Nahm 《Journal of the American Ceramic Society》2003,86(8):1395-400
Microstructural characterizations on the (1− x )La2/3 TiO3 · x LaAlO3 (LTLA) system were conducted using transmission electron microscopy. The presence of La2 Ti2 O7 and La4 Ti9 O24 phases in pure La2/3 TiO3 is confirmed by the electron diffraction pattern. When x = 0.1, the ordering due to the A-site vacancies could be confirmed by the presence of antiphase boundaries (APBs) and return ½(100) superlattice reflection. As x increases, the ordering decreases and finally disappears when x = 0.6. The tilting of oxygen octahedra could be demonstrated by the presence of the ferroelastic domains in the matrix and return ½(111) and return ½(110) superlattice reflections in selected area electron diffraction patterns. In pure LaAlO3 , only the antiphase tilting of oxygen octahedra is present due to the presence of return ½(111) superlattice reflection. In the LTLA system of x = 0.1, both the antiphase and in-phase tiltings of the oxygen octahedra are involved; however, in the range of x from 0.3 to 0.9, the antiphase tilting of oxygen octahedra has appeared. The growth of the ferroelastic domains is influenced by the APBs in the matrix. 相似文献
15.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
16.
Jalajakumari Nair Padmakumar Nair Fujio Mizukami Jan G. Van Ommen Giel B. M. Doesburg Julian R. H. Ross Anthonie J. Burggraaf 《Journal of the American Ceramic Society》2000,83(8):1942-1946
Pure Al2 O3 and different compositions of La2 O3 –Al2 O3 samples have been prepared through coprecipitation. Even after heating at 1300°C, the compositions La2 O3 ·11Al2 O3 and La2 O3 ·13Al2 O3 had higher surface area compared to the pure Al2 O3 and the La2 O3 ·Al2 O3 composition. Ethanol washing is an effective way for improving the textural stability of pure Al2 O3 and La2 O3 –Al2 O3 samples. The effect of steam on the thermal stability of La2 O3 ·11Al2 O3 has also been studied. La2 O3 ·11Al2 O3 sample is found to be stable in steam. 相似文献
17.
Kjell Wiik Christian R. Schmidt Sonia Faaland Senem Shamsili Mari-Ann Einarsrud Tor Grande 《Journal of the American Ceramic Society》1999,82(3):721-728
Sintered submicrometer powder mixtures of strontium-substituted lanthanum manganite and yttria-stabilized zirconia have been studied in order to investigate the chemical stability of these materials as respectively electrode and electrolyte in solid oxide fuel cells. Formation of secondary phases was observed after 1 h heat treatment at 1350°C and more than 13 h at 1200°C. La2 Zr2 O7 was formed in mixtures with LaMnO3 at 1350°C, while SrZrO3 was formed in mixtures containing La0.6 Sr0.4 MnO3 or La0.4 Sr0.6 MnO3 . Only minor amounts of secondary phases were observed in mixtures with La0.7 Sr0.3 MnO3 . Chemical analysis revealed considerable interdiffusion between the primary phases as well as A-site deficiency of LaMnO3 and La0.7 Sr0.3 MnO3 when exposed to cubic zirconia. The oxidative/reductive nature of the chemical reaction between strontium-substituted lanthanum manganite and yttria-stabilized zirconia is discussed in relation to the Sr content in LSM. The lattice parameter of cubic zirconia was observed to be quite sensitive to the interdiffusion and is an excellent tool for investigating reactions on heterophase interfaces involving stabilized zirconia. 相似文献
18.
Michael Rozumek Peter Majewski Linda Sauter Fritz Aldinger 《Journal of the American Ceramic Society》2004,87(4):662-669
Ceramic samples of the melilite-type La1+ x Sr1– x Ga3 O7–δ ( x =−0.15 to 0.60) compound were prepared by conventional ceramic processing. Sintering characteristics and microstructural evolution were studied. A phase diagram study was performed to establish the solid solubility limits as a function of the La:Sr ratio. Structural investigations of the Dalton composition as well as strontium- and lanthanum-rich samples entailed X-ray, neutron, and electron diffraction techniques at ambient and elevated temperatures. The homogeneity region was remarkably broad ( x =−0.15 to 0.60) with no changes in space group observed. A small shrinkage of the unit cell was found with increased lanthanum content. Phase transitions at ambient and intermediate temperatures did not occur. 相似文献
19.
Michael Rozumek Peter Majewski Heike Schluckwerder Fritz Aldinger Klaus Künstler Gerhard Tomandl 《Journal of the American Ceramic Society》2004,87(9):1795-1798
Ceramics of the melilite-type compound La1+ x Sr1− x Ga3 O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x =−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four-point direct-current conductivity measurements and electromotive force measurements. La1+ x Sr1− x Ga3 O7−δ samples exhibited a p -type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C. 相似文献
20.
Riham Michelle Morcos Jean Tangeman Sergey Ushakov Alexandra Navrotsky 《Journal of the American Ceramic Society》2008,91(4):1088-1094
A series of La2 O3 –HfO2 –SiO2 glasses, approximately along the join 0.73SiO2 –0.27( x HfO2 –(1− x )La2 O3 ), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B2 O3 ) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO2 content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO2 content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO2 content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon. 相似文献