共查询到20条相似文献,搜索用时 15 毫秒
1.
A novel preparation route to the perovskite materials Ca0.3La0.7CrO3, Sr0.16La0.84CrO3, and Sr0.2La0.8MnO3 is described. The method produces the phase pure perovskite phases after calcination at 700°C for 2 hours. The powders produced are unagglomerated, and consist of hollow spherical particles 0.15 m in diameter. EDX has shown that the careful control of reaction conditions is vital to control the phase composition, and that small changes in stoichiometry result in the production of unsinterable powder. 相似文献
2.
The sintering behavior of (La0.7Sr0.3)xCrO3 (0.95 x 1.05) is investigated to compare liquid phase sintering phenomena occuring in stoichiometric and non-stoichiometric compositions. Shrinkage analysis revealed marked contrast between the densification characteristics of the A-site enriched (x > 1.00) and A-site depleted (x < 1.00) materials. A-site depleted samples typically exhibited a single liquid phase sintering event at 1250 °C attributed to the melting of an exsoluted SrCrO4 phase. A-site enriched samples indicated two rapid shrinkage events due to the melting of SrCrO4, and a Sr2.67(CrO4)2 phase with a melting temperature of 1450 °C. Sr2.67(CrO4)2 was shown to evolve from a decomposition reaction between SrCrO4 and La2CrO6, detected together in A-site enriched samples from 800–1000 °C. Maximum densities (93% theoretical density) were achieved for (La0.7Sr0.3)xCrO3 x = 1.00 after sintering at 1700 °C for two hours. 相似文献
3.
The perovskite powders Ca0.3La0.7CrO3 and Sr0.16La0.84CrO3 have been prepared using hydrothermal processing. The solid solutions were not formed directly in the autoclave, but the hydrothermally produced powders required calcination at a greatly reduced temperature to form the perovskite phase, reducing the tendency to produce hard agglomerates. Pellets with densities in excess of 95% TD were produced. 相似文献
4.
Phase relationships in the La1?xSrxCrO3 (0.25 ≤ x ≤ 0) system have been investigated. Substitution of Sr into LaCrO3 leads to a phase region with rhombohedral symmetry at room temperature which is oxygen-deficient under strongly reducing conditions. The orthorhombic structure of LaCrO3 and the rhombohedral structure of La0.75Sr0.25CrO3 have been refined by profile fitting of neutron powder diffraction data. 相似文献
5.
In order to identify new cathode compositions for the high temperature solid oxide fuel cell, we have investigated the effect of the trivalent cations Al and Ga at the Mn site of the well-studied cathode composition La0.84Sr0.16MnO3. All the compositions have been prepared by the low temperature citrate-nitrate auto-ignition process and sintered within the temperature range of 1150-1350 °C for 4 h. In order to understand the compatibility of the prepared samples as alternative cathode materials, we compared their electrical conductivity and thermal expansion coefficient with those of La0.84Sr0.16MnO3 and yttria-stabilized zirconia. A 10 mol% Al doped La0.84Sr0.16MnO3 composition exhibited a conductivity of around 122 S cm−1 at 950 °C and a thermal expansion coefficient of 11.04 × 10−6 K with a minimum reactivity towards yttria-stabilized zirconia. Though the conductivity of the new composition is lower than that of La0.84Sr0.16MnO3 (169 S cm−1 at 950 °C), it is still high enough for use as a cathode material. 相似文献
6.
Solid oxide fuel cell (SOFC) interconnect materials, strontium and calcium doped lanthanum chromite, were synthesized to investigate the effect of dopant content and sintering temperature on their sinterability. The results show that approximately 96% of the theoretical density could be achieved when LaCrO3, doped with 30 mol% Ca, was sintered in air at 1400°C. However, to get the same sintered density for the strontia doped material, a 1700°C sintering temperature had to be used. The effect of sintering temperature on the fracture strength was also investigated. A maximum fracture strength of 234 MPa for La0.7Sr0.3CrO3– and 256 MPa for La0.7Ca0.3CrO3–were obtained for both samples sintered at 1700°C. 相似文献
7.
Perovskite-type lanthanum chromium-based oxide films prepared by ultrasonic spray pyrolysis 总被引:1,自引:0,他引:1
Ultrasonic spray pyrolysis was used to form 2–8 m thick LaCrO3 films on different substrates from La(CrO4)(NO3)·nH2O precursor films. There was an optimum substrate temperature for the formation of uniform precursor films by the spray pyrolysis. When the substrate temperature was lower than 250 °C, dry precursor films were not formed, while above 250 °C the deposition rate decreased with substrate temperature. The precursor films were converted to perovskite-type oxide films by heat treatment at 800 °C in a nitrogen atmosphere. Both A-site substituted (La0.8Ca0.2) CrO3 and B-site substituted La(Cr0.5Mn0.5)O3 oxide films were formed in a similar manner. Electronic conductivity of the oxide films was improved by repetitions of the spray pyrolysis and heat treatment in nitrogen. 相似文献
8.
The mechanical, electrical and thermal properties of alkaline earth metal (Mg, Ca and Sr)-doped LaCrO3 have been examined as separators in planar-type high-temperature solid oxide fuel cells. The maximum three-point bending
strength at 1000°C in air was measured and found to be 186 MPa for LaCr0.9Mg0.1O3, 36 MPa for La0.9Ca0.1CrO3 and 77 MPa for La0.9Sr0.1CrO3. The La0.8Sr0.2CrO3 separator placed in both an oxidizing and a reducing environment at 1000°C showed almost the same electrical conductivities
of the H2 atmosphere, and the conductivity was independent of sample thickness in the range 0.5–3.0 mm. For all the doped LaCrO3 perovskites, a difference between the thermal expansion behaviours of air and the H2 atmosphere was observed. In particular, the thermal expansion slope for the first heating cycle under the H2 atmosphere showed a marked change. The volume changes were due to the formation of oxygen defects in the perovskite structure.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
9.
Lanthanum chromate (LaCrO4) was synthesized as a low temperature ( < 700 °C) intermediate to perovskite-type, lanthanum chromite (LaCrO3). The lattice parameters, atom positions and bond lengths determined from X-ray powder diffraction show that LaCrO4 forms a monazite-type crystal structure. Lanthanum chromate forms a solid solution with Ca, having a solubility between 10 and 20 at%. Thermal analysis shows that at ambient oxygen pressure, LaCrO4 transforms to LaCrO3 at a temperature near 700 °C. It also indicates that (La,Ca)CrO4 initially transforms to LaCrO3 and CaCrO4 with the subsequent formation of a (La,Ca)CrO3 solid solution. Evidence of Ca segregation to the surface of (La,Ca) CrO3 particles is given by Auger electron spectroscopy and scanning electron microscopy.[/p] 相似文献
10.
Byoung I. Lee 《Materials Research Bulletin》2008,43(2):207-221
Effects of solvent and chelating agent on synthesis of La0.8Sr0.2CrO3−δ perovskite are reported. Samples are synthesized using a solvent (ethylene glycol or 2-methoxyethanol) and a chelating agent (acetylacetone, citric acid or ethylene diamine tetraacetic acid) by polymeric-gel method, and characterized by X-ray diffractometry and Fourier-transform infrared spectroscopy. Citric acid to metal cations molar ratio (Rc) is varied for ethylene glycol-citric acid system. Samples are mainly orthorhombic perovskite. SrCrO4 is appeared as a secondary phase and found to be the lowest for ethylene glycol-citric acid combination with Rc equal to 7. Crystallographic parameters of perovskite phase are determined and compared with those of LaCrO3. A mechanism employing a partial-charge model, chelating effect and solvent-cage effect is proposed to explain the results. Effect of sintering temperature on phase, relative density and morphology of samples prepared using ethylene glycol and citric acid (Rc = 7) is also reported. 相似文献
11.
E. M. Dedlovskaya N. P. Kuz'mina A. B. Antipov A. N. Grigor'ev L. I. Martynenko 《Inorganic Materials》2002,38(12):1277-1283
Ultrafine La0.7Sr0.3MnO3 powders were prepared via homogenization in chelate solutions, followed by microwave dehydration, using polynuclear heterometallic diethylenetriaminepentaacetates as precursors. To assess the effect of the dehydration procedure on the phase composition and grain size of La0.7Sr0.3MnO3 ceramics, three routes were tested: concentration of chelate solutions by evaporation until the formation of a glassy precursor, microwave dehydration of chelate solutions, and a combination of gelation and microwave dehydration. Phase-pure La0.7Sr0.3MnO3 with a crystallite size of 30–40 nm (as determined by transmission electron microscopy) could be obtained via microwave dehydration of heterobimetallic precursor solutions, followed by calcination at a temperature as low as 800°C. 相似文献
12.
Solid solution of (1−x)LaCrO3–xBiCrO3 (x = 0, 0.10, 0.15, 0.20 and 0.25) was prepared via the citrate–nitrate combustion synthesis. Pure perovskite phase was obtained
at 800 °C, a much lower synthesis temperature than that needed in the solid-state reactions. The thermodynamics of phase formation
and the ceramic sintering mechanism were investigated. The substitution of Bi3+ for La3+ was found to give a separate exothermic decomposition event in the gels and the precursor did not produce a transient liquid
phase while heating to 1200 °C, as was found in ceramics prepared by solid state reaction. This finding shows that the role
of Bi2O3 in the sintering of the La1−x
Bi
x
CrO3 ceramics depends on the processing method. 相似文献
13.
A novel approach to synthesize a single-phase orthorhombic perovskite lanthanum chromite LaCrO3 clusters doped with Sm3+ and Sr2+ ions via gel combustion route was reported. The producing materials were synthesized using metal nitrates as oxidizers and triethanol amine (TEA), N-butyl amine (NBA) or ethylene diamine (EDA) as a fuel. The effect of the annealing temperature, type of organic fuel and the variation of the samarium and/or strontium substitution and its impact on crystal structure, crystallite size, microstructure and magnetic properties of the LaCrO3 powders formed was systematically studied. The results revealed that a well crystalline single phase of pure LaCrO3 can be achieved at annealing temperature from 800 to 1000 °C for 2 h. Moreover, each organic carrier materials exhibited a different degree of effectiveness in the synthesis of the mixed oxide powders. The crystal structure was influenced by doped Sm3+ and/or Sr2+ ions. The crystallite size of the produced powders was increased with the increase the annealing temperature, increasing the Sm3+ ion and the decrease of Sr2+ ion substitution. The microstructures of the produced powders were found to be nanoclusters octahedra-like shaped. The saturation magnetization of the LaCrO3 powders increased continuously with an increase in the Sm3+ ion concentration and it decreased with an increase in the Sr2+ ion up to 0.3 at annealing temperature of 1000 °C for 2 h. The maximum saturation magnetization (0.279 emu/g) was achieved at the Sm3+ ion molar ratio 0.3 and annealing temperature 1000 °C. Moreover, wide coercivities can be obtained at different synthesis conditions (49.25 to 522 Oe). 相似文献
14.
《Materials Letters》2004,58(12-13):1964-1970
The effects of Co and Fe dopants with the amount of 20 and 40 mol% on the properties of La0.84Sr0.16MnO3 were investigated. All compositions were prepared by conventional mixed oxide process and sintered at 1450 °C. The structure of undoped and Co-doped compositions was found to be monoclinic. In addition, the second phase was observed in these sintered compositions. The conductivity of doped materials decreased as compared to that of La0.84Sr0.16MnO3. The SEM microstructure showed the decrease of grain size as Co content increased. The thermal expansion coefficient (TEC) tended to increase as Co content increased. In contrast, the monoclinic and orthorhombic structures were found in 20 and 40 mol% Fe-doped La0.84Sr0.16MnO3. The amount of second phase in sintered composition depends on the amount of Fe content. The conductivity at 1000 °C decreased, but the grain size increased as Fe content increased. The thermal expansion coefficient slightly changed with Fe addition. 相似文献
15.
For the preparation of precursors for fine perovskite-type (0.05 mol) materials, the metal nitrates were completely dissolved in a water solution (total 100 ml) with organic solvent of ethylene glycol (EG), diethylene glycol (DEG), or glycerin (GL), and then dried at 120 °C. In the case of a La–Fe precursor without organic solvent, LaFeO3 was not the main phase for the calcined materials even at 1000 °C. However, the LaFeO3 single phase was obtained by mixing a small amount of organic solvent EG (≥10 ml), DEG(≥5 ml), and GL(≥5 ml) into the solution. In the case of EG, clear XRD peaks of the LaFeO3 single phase were obtained by calcination even at 350 °C. A higher calcination temperature for the formation of the LaFeO3 phase was needed with an increase in the amount of the mixed organic solvent. The oxygen in these organic molecules would act to coordinate to the metal ions instead of nitric acid ions to form a quasi-polymer containing metal ions in a random position, because the nitrogen elemental ratio in the precursor decreased with the amount of added organic solvent. The elemental distribution of La and Fe was highly homogeneous for the decomposed sample. The La1−XSrXMnO3 system was also examined by this method using GL. A single perovskite-type phase formed even for calcination at 700 °C. 相似文献
16.
Solid oxide fuel cells (SOFC) require an interconnect for fabrication into stacked cells. This is typically La(Sr, Ca)CrO3, of which much data on the electrical and physical properties already exists. However, very little information exists on the high temperature mechanical properties of the material, which is a necessity for future design improvements. La1–x
Sr
x
Cr1–y
Co
y
O3 samples were fabricated into green dry-pressed bars and pellets, and sintered under various heating and cooling regimes. The sinterability and high temperature mechanical properties of the material was then investigated as a function of the dopant concentration. It was observed, for example, that the modulus of rupture of the dry pressed La0.7Sr0.3Cr1–yCoyO3 (y 0.3) gave a value of over 110 MPa at 1000 °C. This paper will provide data on the high temperature mechanical properties of the material and its application to the SOFC system. 相似文献
17.
In this study, ultrafine powder of mixed Sr- and Ca-doped lanthanum chromite with two different compositions (La0.7Sr0.1Ca0.2CrO3 and La0.7Sr0.2Ca0.1CrO3) and average particle size of 150 nm was successfully synthesized by the simple process of glycine nitrate. The samples were characterized by thermal analysis, X-ray diffraction, and nitrogen adsorption–desorption, scanning and transmission electron microscopy. The synthesized ultrafine powders with perovskite type crystal structure and some SrCrO4 or CaCrO4 phases were cold isostatically pressed at 200 MPa, and then sintered in air at 1400 °C for several time periods (1–10 h). Relative density measurements were conducted by Archimedes method. The maximum relative density for both samples obtained after sintering in air at 1400 °C for 10 h was 98.2 % of the theoretical density and the average grain size of the sintered pellets was about 2 μm. In addition, the effects of composition on phase transition behavior and electrical properties were studied. 相似文献
18.
A mild hydrothermal method has been adopted to prepare La0.5Sr0.5MnO3 and La0.5Ba0.5MnO3, which is of interest for a number of possible applications. The results from X-ray diffraction (XRD) indicate that in the present work the temperature of 200 and 240 °C are sufficient to prepare phase pure La0.5Sr0.5MnO3 and La0.5Ba0.5MnO3 crystals. At 200 °C, La0.5Sr0.5MnO3 nanowires are obtained. The average width and length of the nanowires are 40 nm and 4 μm, respectively. At 240 °C, La0.5Ba0.5MnO3 powders obtained have a cubic structure with the average size of 3-5 μm. 相似文献
19.
Preparation of Barium Strontium Titanate Ceramic by Sol-Gel Method and Microwave Sintering 总被引:1,自引:0,他引:1
Wen Yang Aimin Chang Bangchao Yang 《Journal of Materials Synthesis and Processing》2002,10(6):303-309
The (Ba,Sr)TiO3 amorphous gel was prepared by sol-gel process and calcined in the 2.45-GHz multimode microwave furnace to synthesize (Ba,Sr)TiO3 nanopowder. The calcination temperature of the (Ba,Sr)TiO3 ceramic powders that convert the material into prevoskite phase can be reduced from 1100°C to 900°C, the nanopowder displays the highest sinterability. Using a new kind of insulator materials made of MgAl2O4–LaCrO3, the crack-free and dense (Ba0.80Sr0.20)TiO3 ceramics with fine grain size (<1 µm) were prepared by microwave sintering at 1310°C for 15 min. The fine (Ba,Sr)TiO3 ceramics sintered by microwave sintering technique display lower dielectric loss than that of conventional samples, indicating a reduction of the influence of defects with the microwave process. 相似文献
20.
La0.7Sr0.3FeO3 nanoparticles assembled nanowires were synthesized by a hydrothermal method assisted with cetyltrimethylammonium bromide (CTAB). The hydrothermal temperature was 180 °C and the annealed temperature was 700 °C. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, composition and structural properties of the materials. The results showed that the La0.7Sr0.3FeO3 nanoparticles assembled nanowires had a high aspect ratio (the largest aspect ratio >100); the size of the nanoparticles was about 20 nm and the diameter of the nanowires was about 100–150 nm. The growth mechanism of La0.7Sr0.3FeO3 nanowires was discussed. Gas sensors were fabricated by using La0.7Sr0.3FeO3 nanowires. Formaldehyde gas sensing properties were carried out in the concentration range of 0.1–100 ppm at the optimum operating temperature of 280 °C. The response and recovery times to 20 ppm formaldehyde of the sensor were 110 s and 50 s, respectively. The gas sensing mechanism of La0.7Sr0.3FeO3 nanowires was investigated. 相似文献