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1.
Based on the conventional interconnect La 0.7Ca 0.3CrO 3−δ, a novel ceramic interconnect for intermediate temperature solid oxide fuel cells was developed. In the air, the electrical conductivities of La 0.7Ca 0.3CrO 3−δ + 5%Ce 0.8Sm 0.2O 1.9 at 600, 700 and 800 °C were 96.7, 146.3 and 687.8 S cm −1, respectively, which increased significantly as compared with La 0.7Ca 0.3CrO 3−δ under the same conditions. Similarly, in pure hydrogen, La 0.7Ca 0.3CrO 3−δ + 3%Ce 0.8Sm 0.2O 1.9 possessed the maximal electrical conductivities which were 4.2, 5.3 and 7.1 S cm −1, respectively at 600, 700 and 800 °C. The crystal structures of La 0.7Ca 0.3CrO 3−δ, La 0.7Ca 0.3CrO 3−δ + 5%Ce 0.8Sm 0.2O 1.9 and La 0.7Ca 0.3CrO 3−δ + 10%Ce 0.8Sm 0.2O 1.9 were single phase with hexagonal symmetry, cubic phase plus some doped ceria impurity and orthorhombic phase plus some doped ceria impurity, respectively. The difference between the crystal structures may account for the difference between the electrical conductivities. The electrical conductivities and sinterability of La 0.7Ca 0.3CrO 3−δ were increased by introducing Ce 0.8Sm 0.2O 1.9, whereas the other properties were not influenced. 相似文献
2.
In this paper, an interconnecting ceramic for solid oxide fuel cells was developed, based on the modification from La 0.7Ca 0.3CrO 3−δ by addition of Ce 0.8Sm 0.2O 1.9. It is found that addition of small amount Ce 0.8Sm 0.2O 1.9 into La 0.7Ca 0.3CrO 3−δ dramatically increased the electrical conductivity. For the best system, La 0.7Ca 0.3CrO 3−δ + 5 wt.% Ce 0.8Sm 0.2O 1.9, the electrical conductivity reached 687.8 S cm −1 at 800 °C in air. In H 2 at 800 °C, the specimen with 3 wt.% Ce 0.8Sm 0.2O 1.9 had the maximal electrical conductivity of 7.1 S cm −1. With the increase of Ce 0.8Sm 0.2O 1.9 content the relative density increased, reaching 98.7% when the Ce 0.8Sm 0.2O 1.9 content was 10 wt.%. The average coefficient of thermal expansion at 30-1000 °C in air increased with Ce 0.8Sm 0.2O 1.9 content, ranging from 11.12 × 10 −6 to 12.46 × 10 −6 K −1. The oxygen permeation measurement illustrated a negligible oxygen ionic conduction, indicating it is still an electronically conducting ceramic. Therefore, this material system will be a very promising interconnect for solid oxide fuel cells. 相似文献
3.
Structures and thermal expansion properties of Ln 2−xCr xMo 3O 12 (Ln = Er and Y) have been investigated by X-ray powder diffraction. Rietveld analysis results of Ln 2−xCr xMo 3O 12 indicate that compounds Er 2−xCr xMo 3O 12 (0 ≤ x ≤ 0.3) and Y 2−xCr xMo 3O 12 (0 ≤ x ≤ 0.2) crystallize in orthorhombic structure and exhibit negative thermal expansion, while both monoclinic and orthorhombic compounds Er 2−xCr xMo 3O 12 (1.7 ≤ x ≤ 2.0) and Y 2−xCr xMo 3O 12 (1.8 ≤ x ≤ 2.0) possess positive coefficient of thermal expansion. The coefficients of linear thermal expansion of orthorhombic Ln 2−xCr xMo 3O 12 change from negative to positive with increasing chromium content. Thermogravimetric and differential scanning calorimetry have been used to study the hygroscopicity and the phase transition temperature. 相似文献
4.
LaMnO 3+δ and La 0.7Ca 0.3MnO 3 were synthesized from La 2O 3(La(OH) 3), CaCO 3 and MnO 2 powder mixture with solid-state reaction technique. X-ray diffraction and thermal analysis were employed in the present study on the process of synthesizing of the two compound powders. The kinetic study on solid-state reaction between La 2O 3 and MnO 2 in the powder mixture was isothermally carried out for LaMnO 3+δ formation. The result showed that the reaction process was controlled by three-dimensional solid-ionic diffusion. Both Jander and Ginstling-Brounstein model can be used to describe the reaction kinetics satisfactorily. The relevant apparent activation energy values obtained were as great as 205 ± 11 and 189 ± 8 kJ/mol. The reaction process of La 0.7Ca 0.3MnO 3 preparation from La 2O 3, SrCO 3 and MnO 2 powder mixture was also studied using X-ray diffraction and thermal analysis. The result indicated that the following steps composed the overall reaction: the decomposition of the reactant; the formation of La 1−xCa xMnO 3+δ; La 2O 3 and Mn 3O 4 reacted with La 1−xCa xMnO 3 to form final La 0.7Ca 0.3MnO 3 phase. The latest step was the most time-consuming one among others in the overall reaction. 相似文献
5.
The magnetic properties and magnetocaloric effect near the critical phase transition temperatures of La 1.4−x
Ce
x
Ca 1.6Mn 2O 7 ( x = 0, 0.2) double layered manganites are analyzed. Polycrystalline nanopowders of La 1.4Ca 1.6Mn 2O 7 and La 1.2Ce 0.2Ca 1.6Mn2O 7 were successfully synthesized by a sol–gel method. The magnetic measurements suggest an antiferromagnetic alignment of the
Ce and Mn moments in La 1.2Ce 0.2Ca 1.6Mn 2O 7. Both Ce 3+ and Ce 4+ ions are present in the doped sample, as indicated by the XPS spectra. A moderate magnetocaloric effect was found for both
samples, with the maximum entropy change located at temperatures near the magnetic transition ones. The high RCP(S) values
together with the broadened magnetic entropy curves suggest the possibility to use these materials for magnetic refrigeration
devices. 相似文献
6.
In this paper, Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ– xSm 0.2Ce 0.8O 1.9 (BSCF– xSDC, x = 0–60 wt.%) composite cathodes were prepared by soft chemical methods, and then examined for potential applications in lower temperature solid oxide fuel cells. Both DC polarization and AC impedance spectroscopy measurements indicated that the addition of SDC electrolyte into BSCF remarkably improved the electrochemical properties. The optimum composition was found to be BSCF–30SDC, which exhibited 5.5 times higher polarization current density and 15.1% polarization resistance, compared with the pure-phase BSCF cathode at 550 °C. 相似文献
7.
Solid oxide fuel cells (SOFC) require an interconnect for fabrication into stacked cells. This is typically La(Sr, Ca)CrO 3, 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. La 1–x
Sr
x
Cr 1–y
Co
y
O 3 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 La 0.7Sr 0.3Cr 1–yCo yO 3 ( 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
8.
Li 1.2+x[Ni 0.25Mn 0.75] 0.8−xO 2 (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li + content on electrochemistry of Li 1.2Ni 0.2Mn 0.6O 2 ( x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO 2 structure (space group R-3 m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li + is possibly incorporated in structure of layered Li 1.2Ni 0.2Mn 0.6O 2 ( x = 0), accompanying oxidization of Ni 2+ to Ni 3+ to form Li 1.2+x[Ni 0.25Mn 0.75] 0.8−xO 2 (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni 3+ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li 1.2+x[Ni 0.25Mn 0.75] 0.8−xO 2 (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li 1.2Ni 0.2Mn 0.6O 2 ( x = 0) in this work delivered the highest discharge capacity of 219 mAh g −1 between 4.8 and 2.0 V. Increasing Li content ( x value in Li 1.2+x[Ni 0.25Mn 0.75] 0.8−xO 2) reduced charge–discharge capacities, but significantly enhancing cycleability. 相似文献
9.
This work is focused on nanocrystalline solid oxide fuel cell synthesis and characterization (SOFC) anodes of La 0.7Sr 0.3Cr 0.4Mn 0.6O 3−δ (perovskite-type) with Nickel. Perovskite-type oxide chemical reactivity, nucleation kinetics and phase composition related with La 0.7Sr 0.3Cr 0.4Mn 0.6O 3−δ–NiO to La 0.7Sr 0.3Cr 0.4Mn 0.6O 3−δ–Ni transformation have been analyzed. SOFC anode powders were obtained by sol–gel synthesis, using polyvinyl alcohol as an organic precursor to get a porous cermet electrode after sintering at 1365 °C and oxide reduction by hydrogen at 800 °C/1050 °C for 8 h in a horizontal tubular reactor furnace under 10% H 2/N 2 atmosphere. Composite powders were compressed into 10-mm diameter discs with 25–75 wt% Ni. 相似文献
10.
Calcium-doped lanthanum chromites, (La 1–x
Ca
x
) (Cr 1–
y Ca y O 3, have been synthesized to investigate effects of calcium doping on sinterability and electrical conductivity. X-ray diffractometric results have revealed that in addition to normal perovskites (La 1–
xCa
x
CrO 3), chromium-deficient perovskites can exist as a single phase in the composition region 0.1 < x < 0.3, although the deficit of chromium is small. These chromium-deficient perovskites show a good sinterability even in air at 1873 K. Electrical conductivity of these perovskites has been measured as functions of temperature and oxygen potential. It has been found that electrical conductivity of the chromium-deficient perovskites increases almost linearly with total calcium content. The magnitudes of electrical conductivity are comparable to those of strontium-doped lanthanum chromites. 相似文献
11.
We have taken advantage of congruent melting behavior of the nonlinear rare-earth oxoborate Ca 4REO(BO 3) 3 family to perfect a process of collective fabrication of self-frequency doubling microchip laser based on Nd:GdCOB (Ca 4Gd 1−xNd xO(BO 3) 3) crystals. The process goes from Czochralski boule to 1 × 3 mm 2 chips perfectly oriented (better than 0.1°) to the phase matching direction (θ=90°, φ=46°) in the XY principal plane, with dielectric mirrors directly deposited on both faces of the chips. 20 mW of self-frequency doubling output power at 530 nm was performed under 800 mW of diode laser as incident pump power at 812 nm. In addition, new compositions from the solid solution Ca 4Gd 1−xY xO(BO 3) 3 (Gd 1−xY xCOB) ( x=0.13, 0.16, 0.44) have been grown by the Czochralski pulling method, in order to achieve noncritical phase matching (NCPM) second harmonic generation of 4F 3/2 → 4I 9/2 Nd 3+ doped laser hosts. Three types of laser wavelengths have been chosen: Nd:YAP (YAlO 3) at 930 nm, Nd:YAG (Y 3Al 5O 12) at 946 nm, and Nd:ASL (Nd ySr 1−x La x−yMg x Al 12−xO 19) at 900 nm. Angular acceptance measurements of these three types of compositions present very large values, compared to pure GdCOB or YCOB oriented in critical phase matching configurations. 相似文献
12.
Perovskite-type oxides BaCe 0.90Sm 0.10O 3−δ (BCS) and BaCe 0.80Gd 0.10Sm 0.10O 3−δ (BCGS) were synthesized by the sol–gel method and characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Using the sintered samples as solid electrolytes and silver–palladium alloy as electrodes, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in a solid-state proton-conducting cell reactor. The maximum rate of production of ammonia was 5.82×10 −9 mol s −1 cm −2. 相似文献
13.
Methane catalytic combustion was carried out over the Ce 0.9–xNi 0.1Ca xO δ (0 < x ≤ 0.3) catalysts prepared by a citric acid complexation–combustion method. When x ≤ 0.1, the presence of Ca can enhance
the surface area and reduce the crystalline size, and improve the reduction of the dispersed NiO species in catalyst, resulting
in an improvement of the catalytic activity of Ce 0.9–xNi 0.1Ca xO δ. The XRD and Raman results show that Ce 0.9–xNi 0.1Ca xO δ (x ≤ 0.1) solid solution can form by Ni and Ca incorporation in the CeO 2 lattices. TEM and etching results reveal that part of Ni disperses well on the surface of Ca-doped sample. FT-IR testing
shows that with an increase in Ca amount (x > 0.1), more carbonate species (mainly carbonate calcium) can form on the catalyst
surface, which would severely debase the catalytic activity of Ce 0.9–xNi 0.1Ca xO δ. 相似文献
14.
La 1.6Sr 0.4NiO 4+δ-Ce 0.8Sm 0.2O 1.9 composite cathodes were prepared successfully using combustion synthesis method for intermediate temperature solid oxide fuel cells. The chemical compatibility, thermal expansion behavior, electrical conductivity and electrode performance were studied. The X-ray diffraction of La 1.6Sr 0.4NiO 4+δ-Ce 0.8Sm 0.2O 1.9 composite result proved a slight reaction between La 1.6Sr 0.4NiO 4+δ and Ce 0.8Sm 0.2O 1.9. Both the thermal expansion coefficient and the electrical conductivity of La 1.6Sr 0.4NiO 4+δ-Ce 0.8Sm 0.2O 1.9 decreased with increasing Ce 0.8Sm 0.2O 1.9 content. AC impedance spectroscopy measurements indicated that the addition of 30 wt% Ce 0.8Sm 0.2O 1.9 to La 1.6Sr 0.4NiO 4+δ exhibited the lowest polarization resistance (0.238 Ωcm 2) at 800 °C in air, which was only one fourth of the La 1.6Sr 0.4NiO 4+δ electrode measured at the same temperature. 相似文献
15.
Hierarchically porous metal oxides are prepared using a novel self-rising approach. The method is ‘hard-template’ free and relatively easy to perform, utilizes inexpensive precursors and processing conditions, and is versatile, thus offering tremendous opportunities with a wide variety of conditions to explore to synthesize single or mixed metal oxides with hierarchically porous structures. Fe 2O 3, Sm 0.2Ce 0.8O 1.9, LaFeO 3, LaCoO 3, and La 0.5Sr 0.5Co 0.5Fe 0.5O 3 have been successfully synthesized while Fe 2O 3 and La 0.5Sr 0.5Co 0.5Fe 0.5O 3 as examples for single and mixed metal oxides have been studied in detail. Sm 0.2Ce 0.8O 1.9 has been applied as electrolyte for solid oxide fuel cells, showing good sinterability and high conductivity. A tentative scheme is provided to illustrate the pore formation mechanism using the self-rising approach. 相似文献
16.
The phase equilibria and crystal structures of mixed oxides in the ternary system La 2O 3-Mn 3O 4-NiO are studied at 1100°C in air. The projection of the La-Mn-Ni-O phase diagram at 1100°C and
= 0.21 × 10 5 Pa onto the metal-composition triangle is found to comprise 12 phase fields. The lattice parameters of La 2NiO 4 (sp. gr. I4/ mmm), La 3Ni 2O 7 (sp. gr. Cmcm), La 4Ni 3O 10 (sp. gr. Cmca), and La 1 + x
Mn 1 − x − y
Ni yO 3 solid solutions (sp. gr. Pnma, −0.04 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.4) are determined. The composition stability limits of La 4Ni 3 − y
Mn yO 10 solid solutions are 0 < y ≤ 0.05. With increasing Ni concentration in La 1 + x
Mn 1 − x − y
Ni yO 3, the metal nonstoichiometry decreases from −0.04 ≤ x ≤ 0.05 at y = 0 to x = 0 at y = 0.4.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 841–848.Original Russian Text Copyright © 2005 by Demina, Cherepanov, Petrov, Klokova. 相似文献
17.
Oxygen non-stoichiometry, electrical conductivity and thermal expansion of La 2−xSr xNiO 4−δ phases with high levels of strontium-substitution (1 ≤ x ≤ 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20–1050 °C. These phases retain the K 2NiF 4-type structure of La 2NiO 4 (tetragonal, space group I4/ mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La 2NiO 4±δ in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni 3+/Ni 4+ to a Ni 2+/Ni 3+ equilibrium on heating. 相似文献
18.
A-site-substituted cerium orthovanadates, Ce 1−x
Ca
x
VO 4, were synthesised by solid-state reactions. At room temperature, the solid solution limit in Ce 1−x
Ca
x
VO 4 series is at x = 0.4125. The crystal structure was analysed by X-ray diffraction and it exhibits a tetragonal zircon structure of space
group I4 1/ amd with a = 7.4004 (1) and c = 6.4983 (6) ? for CeVO 4. The UV–Visible absorption spectra indicated that the compounds have band gaps at room temperature in the range of 4.2–4.5 eV.
Conductivity measurements were performed for the first time up to the calcium solid solution limit in both air and dry 5%
H 2/Ar with conductivity values at 600 °C ranging from 0.3 to 20 mS cm −1 in air to 3 to 30 mS cm −1 in reducing atmosphere. In general, the conductivity of Ca-doped CeVO 4 is higher in air but lower in a reducing atmosphere comparing to pure CeVO 4. The H 2/air electrochemical cell measurement indicates that the conduction of sample Ce 0.7Ca 0.3VO 4 is electronic dominant. Samples Ce 0.9Ca 0.1VO 4 and Ce 0.8Ca 0.2VO 4 are redox stable at a temperature below 600 °C although the conductivity is not high enough to be used as an electrode for
solid oxide fuel cells. 相似文献
19.
Polycrystalline powders of rare-earth doped La1?xGdxB3O6 (0?≤?x?≤?0.2) and La1?xSmxB3O6 (0.0?≤?x?≤?0.1) phosphors were successfully prepared by a B2O3 flux method. All the phosphor samples are well characterized by powder X-ray diffraction (XRD), infrared (IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) methods and fluorescence lifetime of Sm3+ ion. The XRD patterns show that La1?xMxB3O6 (M?=?Gd and Sm) adopt monoclinic with the I2/a space group. The SEM–EDS results confirmed the doping of Gd and Sm into LaB3O6 lattice. The IR and Raman spectra of these solid solutions gave distinctive bands corresponding to planar BO3 and tetrahedral BO4 groups. The photoluminescence (PL) spectra of La1?xGdxB3O6 gave a strong emission band, 6PJ?→?8S7/2, at 310 nm. The PL spectra of La1?xSmxB3O6 phosphor showed orange-red emission at 598 nm when excited using light of wavelength of 402 nm. The results were obtained by the transition 4G5/2?→?6H7/2 of Sm3+ ions. The influence of dopant concentration on the emission profiles was studied. The ESR spectra of La1?xGdxB3O6 (x?=?0.02) gave a typical U-spectrum and spin-Hamiltonian parameters are deduced. 相似文献
20.
The single phase of LiCo 0.3−xGa xNi 0.7O 2 ( x = 0, 0.05) was synthesized by a sol–gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The powders are homogeneous and have a good-layered structure. The synthesized LiCo 0.25Ga 0.05Ni 0.7O 2 exhibits better electrochemical performance with an initial discharge capacity of 180.0 mAh g −1 and a capacity retention of 95.2% after 50 cycles between 2.8 and 4.4 V at 0.2 C rate. The study on the structural evolution of the material during the cycling shows that Ga-doping improves the structure stability of LiCo 0.3Ni 0.7O 2 at ambient temperature and 55 °C. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo 0.3Ni 0.7O 2 but also promotes the Li + diffusion in LiCo 0.3Ni 0.7O 2. Furthermore, thermal stability of the charged LiCo 0.25Ga 0.05Ni 0.7O 2 is improved, which may be attributed to the retard of O 2 evolution in LiCo 0.3Ni 0.7O 2 and the suppression of electrolyte oxidation during cycling by Ga-doping . 相似文献
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