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1.
La1-xAxCoO3-δ (A = Sr, Ba) nanoparticles used as an inert anode in molten salts were characterized using phonon vibrations, and their compositions and morphologies were investigated. These nanoparticles were used for nanostructure fabrication of an inert anode to reduce oxide ion transportation. The singularity structure changes with increasing Sr ion content in La1-xSrxCoO3-δ nanoparticles showed a transient of spin state change from a low-spin state to intermediate- and/or high-spin states. The valencies of Co ion in La1-xSrxCoO3-δ were 3.2 and 3.3 for La0.8Sr0.2CoO3-δ and La0.6Sr0.4CoO3-δ, respectively, suggesting that oxygen defects were introduced by Sr ion doping in La1-xSrxCoO3-δ nanoparticles. In contrast, the valencies of Co ion in La1-xBaxCoO3-δ were 3.1 and 3.0 for La0.5Ba0.5CoO3-δ and La0.4Ba0.6CoO3-δ, respectively, suggesting that oxygen defects were introduced slightly by Ba ion doping in La1-xBaxCoO3-δ nanoparticles. The isotropic phonon vibrations of La1-xAxCoO3-δ nanoparticles were estimated using high-temperature synchrotron radiation X-ray diffraction measurements. Crystal anisotropy measurements of phonon vibrations indicated that the oxide ions diffused preferentially along the (a, b) plane in the La1-xSrxCoO3-δ crystal lattice and toward the c-axis direction in the La1-xBaxCoO3-δ crystal lattice. These results suggest that the oxide ion transportation was curtailed using layered nanoparticles to fabricate an inert anode. 相似文献
2.
Phase equilibria in the La–Sr–Co–Ni–O system were studied in air at 1100°. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La 1-xSr xCo 1-yNi yO 3- and (La 1-xSr x) 2Co 1-yNi yO 4 solid solutions were determined by Xray powder diffraction analysis. La 1-xSr xCo 1-yNi yO 3- solid solutions with 0 x 0.5 have a distorted rhombohedral perovskitelike structure ( R
c space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x < 0.5 have an ideal cubic structure ( Pm3 m space group). (La 1-xSr x) 2Co 1-yNi yO 4 crystals have a tetragonal K 2NiF 4 type unit cell ( I4/ mmm space group). The relationships between unit cell parameters and compositions were obtained for singlephase La 1-xSr xCo 1-yNi yO 3- and (La 1-xSr x) 2Co 1-yNi yO 4 samples. The existence regions of La 1-xSr xCo 1-yNi yO 3- and La 1-xSr x) 2Co 1-yNi yO 4 solid solutions were distinguished on P–T phase diagrams. 相似文献
3.
Powder X-ray diffraction measurements of La 1-xY xAlO 3 suggested that the space groups of x=0.3 and 0.9 samples are Pnma at room temperature and that a structural phase transition occurs from R-3c to Pnma above 200
K in x=0.1 sample. The unit cell volumes of x=0.1, 0.3, and 0.9 samples at 20 K are larger than the average one estimated from the volumes of LaAlO 3 and YAlO 3. The heat capacities of x=0.1 and 0.3 samples are larger than those of LaAlO 3 in the range 3-20 K. On the other hand, the volumes of Y 1-xLu xAlO 3 ( x=0.1, 0.3, and 0.5) at 20 K are close to the average one and the heat capacity increased as x is increased in the range 3-20 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
The oxidative coupling of methane over (Bi 2O 3) 1-x(WO 3) x (x=0.2, 0.3, 0.4) oxygen ion conductive oxide catalysts irradiated by microwave has been studied. Compared with a conventional
heating mode, the temperature of the catalytic bed is much lower with microwave irradiation and there is a change in selectivity
favoring the production of C 2 products. 相似文献
5.
DSC was used for heat capacity measurements of pure RuO 2 in the temperature range from 300 to 1170 K of solid solutions corresponding to the compositions of (Ti 1−x Ru x )O 2 ( x ≤0.15 and x ≥0.85) and in the temperature range from 300 to 1550 K of pure TiO2. The analysis of experimental data obtained within ±2%
of accuracy has shown that the characteristic temperatures representing the harmonic lattice vibrations do not strongly depend
on the chemical composition x . It was demonstrated that non-harmonic heat capacity is strongly correlated to x. The existence of additional excess heat
capacity was observed with the mixed oxide solid solution samples of low Ru content and explained by the defect formation
model.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
采用甘氨酸-硝酸盐法合成了中温固体氧化物燃料电池阴极材料La 1.6Sr 0.4Ni 1-xCu xO 4 (x=0.2, 0.4, 0.6,0.8), 利用X射线衍射(XRD)和扫描电子显微镜(SEM)对其结构和微观形貌进行了表征. 结果表明, 该阴极材料与固体电解质Ce 0.9Gd 0.1O 1.95(CGO)在1000 °C烧结时不发生化学反应, 且烧结4 h 后, 二者之间可形成良好的接触界面. 利用电化学交流阻抗谱技术对阴极材料的电化学性能进行研究, 结果显示, 当Cu离子掺杂量(x)为0.6 时, La 1.6Sr 0.4Ni 0.4Cu 0.6O 4阴极具有最小的极化电阻, 在空气中当测试温度为750 °C时, 极化电阻为0.35 Ω·cm 2. 在不同氧分压条件下电化学阻抗谱分析结果表明, 电极上的两个氧还原反应主要包含氧离子从三相界面向电解质CGO 转移的过程和电荷的迁移过程, 其中电荷的迁移过程为电极反应的速率控制步骤.La 1.6Sr 0.4Ni 0.4Cu 0.6O 4电极在空气中700 °C和阴极电流密度为45 mA·cm -2时, 阴极过电位为45 mV. 本研究的初步结果表明La 1.6Sr 0.4Ni 1-xCu xO 4材料是一种电化学性能较为优良的新型中温固体氧化物燃料电池(IT-SOFC)阴极材料. 相似文献
7.
Summary In the present study, the effect of the partial replacement of Pb 2+ by La 3+ in the lead magnesium niobate Pb(Mg 1/3Nb 2/3)O 3 (PMN) perovskite structure was examined, taking into account the Mg-source. Pure lead magnesium niobate (PMN) and lanthanum-modified lead magnesium niobate (PLMN) having composition (Pb 1-xLa x) (Mg 1+x/3Nb 2-x/3)O 3 with x=0.2 were elaborated. The phase formation was investigated by DTA/TG methods correlated with X-ray diffraction, performed on materials obtained in non-isothermal conditions. The diffraction data for the ceramics obtained by isothermal treatments emphasized the influence of the lanthanum on the crystal structure, inducing the doubling of the unit cell parameter. SEM investigations pointed out the lanthanum inhibitor effect on the grain growth process, leading to an uniform grain distribution. 相似文献
8.
采用燃烧法制备了Sr掺杂钙钛矿型氧化物La 1-xSr xFeO 3(x=0,0.3,0.5,0.9)载氧体,对载氧体分别进行X射线衍射、扫描电镜和H 2程序升温还原反应表征,在热重循环装置和固定床反应装置上考察甲烷与载氧体晶格氧的部分氧化反应.结果表明,La 1-xSr xFeO 3氧化物中的晶格氧适用于甲烷部分氧化制合成气,晶格氧的得失是一个可逆过程,Sr的掺杂提高了载氧体的供氧能力,5次循环后载氧体得失晶格氧的能力没有明显的衰减.从甲烷转化率、n(H 2)/n(CO)比以及H 2和CO的选择性等方面来考虑,x=0.3-0.5比较理想,甲烷转化率维持在70%左右,气体产物中n(H 2)/n(CO)约为2,CH 4没有发生明显的裂解. 相似文献
9.
Colossal negative thermal expansion (NTE) with a volume contraction of about 8 %, the largest value reported so far for NTE materials, was observed in an electron‐doped giant tetragonal perovskite compound Pb 1?xBi xVO 3 ( x=0.2 and 0.3). A polar tetragonal ( P4 mm) to non‐polar cubic structural transition took place upon heating. The coefficient of thermal expansion (CTE) and the working temperature could be tuned by changing the Bi content, and La substitution decreased the transition temperature to room temperature. Pb 0.76La 0.04Bi 0.20VO 3 exhibited a unit cell volume contraction of 6.7 % from 200 K to 420 K. Interestingly, further gigantic NTE of about 8.5 % was observed in a dilametric measurement of a Pb 0.76La 0.04Bi 0.20VO 3 polycrystalline sample. The pronounced NTE in the sintered body should be attributed to an anisotropic lattice parameter change. 相似文献
10.
The sample with in the general formula Bi 2-xPb xSrV 2O 9, where x = 0.0, 0.05, 0.1, 0.2, 0.3, and 0.6 mol were synthesized by the high temperature solid state reaction and firing method. The X-ray diffractograms confirmed the formation of single phased layered perovskite in all samples. TGA and DTA thermal analyses on the green samples included steps of thermal analysis of strontium carbonate, bismuth carbonate, ammonium vanadate, lead oxide and finally on the high temperature solid state formation. The effect of lead dopings on the sintering, structural and micro-structure, properties of 212BiSrV-ceramics were investigated. The infrared absorption spectra show a series of vibrational modes within the range of 400–1600 cm ?1. 相似文献
11.
Two mixed oxide systems La 2- xSr xCuO 4±
λ (0.0⩽x⩽1. 0) and La 2-xTh xCuO 4±
λ (O. O⩽x⩽ 0.4) with K 2NiF 4 structure were prepared by varying x values. Their crystal structures were studied by means of XRD and IR spectra. The average valence of Cu ion at B site, nonstoichiometric
oxygen (λ) and the chemical composition in the bulk and on the surface of the catalysts were measured by means of chemical
analysis and XPS. The catalytic behavior in reaction CO+NO was investigated under the regular change of average valence of
Cu ion at B site and nonstoichiometric oxygen (λ). Meanwhile, the adsorption and activation of the small molecules NO and
the mixture of NO+CO over the mixed oxide catalysts were studied by means of MS-TPD. The catalytic mechanism of reaction NO+CO
over these oxide catalysts were proposed; and it has been found that, at lower temperatures the activation of NO is the rate
determining step and the catalytic activity is related to the lower valent metallic ion and its concentration, while at higher
temperatures the adsorption of NO is the rate determining step and the catalytic activity is related to the oxygen vacancy
and its concentration.
Project supported by the National Natural Science Foundation of China. 相似文献
12.
Pb 1-xZn xS (x = 0 to 0.4 in steps of 0.1) ternary semiconductor material shave been prepared by co-precipitation method. The structural and electrical studies have been carried out to understand the influence of Zinc on activation energy. X-ray diffractograms showed that the Pb 1-xZn xS compounds are polycrystalline in nature with cubic phase. The temperature-dependent conductivity measured in the range 300–4 K showed a change in the conduction mechanism at 62 K and 31 K. The activation energies evaluated at low and very low temperature regions. Activation energy increases and conductivity decreases with the increase of Zn in Pb 1-xZn xS compounds. The samples are exhibiting low freezing temperature points indicating their capability to use in low temperature applications. 相似文献
13.
Crystals of Lu 1-xSc xBO 3:Ce (x = 0.2, 0.5, 0.7) are prepared by the Czochralski method and characterized by single crystal XRD, Raman spectroscopy, and vacuum UV excitation spectroscopy. 相似文献
14.
Polycrystalline samples of rare-earths molybdates and tungstates, i.e., CdRE 4Mo 3O 16 (RE = Eu, Gd, Y, Ho) and Pb 1–3x□ xEu 2xWO 4 (0 < x ≤ 0.1296 and □ denotes cationic vacancies) have been successfully prepared by high-temperature annealing of adequate CdMoO 4/RE 2MoO 6 and PbWO 4/Eu 2(WO 4) 3 mixtures, respectively. According to the X-ray diffraction analysis, the CdRE 4Mo 3O 16 compounds crystallize in a cubic, fluorite-related-type structure with space group \(Pn\bar{3}n\). In turn, new Pb 1–3x□ xEu 2xWO 4 phases crystallize in the scheelite-type, tetragonal symmetry, space group I4 1/ a. Cadmium and rare-earth molybdates decompose in the solid state and the solid products of their decomposition are two RE molybdates, i.e., RE 2MoO 6 and RE 2(MoO 4) 3. Thermal stability of CdRE 4Mo 3O 16 decreases with decreasing of RE 3+ radius. The melting point of each sample of Pb 1–3x□ xEu 2xWO 4 solid solution is lower than melting point of pure matrix, i.e., PbWO 4 (1116 °C), and it decreases with increasing in Eu content. Both CdRE 4Mo 3O 16 as well as Pb 1–3x□ xEu 2xWO 4 samples are insulators, and their optical band gap ( E g) is bigger than 3 eV. 相似文献
15.
利用X射线衍射、N 2吸附等温线、X射线光电子能谱、X射线吸收谱、H 2-程序升温还原、甲基橙选择化学吸附和等电点测定等方法研究了共沉淀方法制备的一系列Ce xTi 1-xO 2复合氧化物的结构. 成功发展了甲基橙选择化学吸附和等电点方法研究Ce xTi 1-xO 2复合氧化物的最外层表面结构, 并定义了“等价CeO 2表面覆盖度”来描述Ce xTi 1-xO 2复合氧化物的最外层表面结构. Ce xTi 1-xO 2复合氧化物 (x ≥ 0.7)形成立方萤石相固溶体, Ce 0.3Ti 0.7O 2表现出纯的单斜相, 而其它复合氧化物表现出混合相. Ce xTi 1-xO 2复合氧化物最外层表面结构的演变行为不同于其体相结构.Ce 0.7Ti 0.3O 2立方萤石相固溶体最外层表面已经部分形成了单斜相Ce 0.3Ti 0.7O 2, 随Ce含量的降低, 单斜相Ce 0.3Ti 0.7O 2从最外层表面向体相生长. Ce xTi 1-xO 2复合氧化物立方萤石相固溶体和单斜相Ce 0.3Ti 0.7O 2分别在相对较低和较高的温度表现出好的还原性能. 上述结果提供了全面和深层次的Ce xTi 1-xO 2复合氧化物结构信息. 相似文献
16.
Studies on the role of oxygen vacancy in structural change of nonstoichiometric perovskites and a property of oxygen-deficient perovskite-related K 2NiF 4 compounds are reviewed.The structural changes on which the authors focused are cation ordering and lattice distortion. The relationship between the distortion and oxygen vacancy was investigated by comparing the structures of Sr 2(Sr 1-xM x)TaO 6-d (M = Ca 2+ and Nd 3+) solid solutions. It was found that distortion of a perovskite-type lattice decreased with an increasing amount of oxygen vacancies. In order to investigate the relationship between the cation ordering on octahedral sites and oxygen vacancy, structures of stoichiometric Sr 2-xLa xCo 1-yTa 1+yO 6 and oxygen-deficient Sr 2-xLa xMg 1-yTa 1+yO 6-d solid solutions were compared. The authors' work reveals that the cation ordering affects the amount of oxygen vacancies in addition to cation charge and size. 相似文献
17.
A system consisting of a solid oxide electrolyte of the Ce 0.9Gd 0.1O 2 − x
(CGO) composition in contact with a two-layer cathode based on a nonstoichiometric composition (La 0.8Sr 0.2) 0.95MnO 3 ± δ (LSM1) and a stoichiometric perovskite La 0.8Sr 0.2MnO 3 ± δ (LSM2) is prepared by the tape-casting process. It was shown that the best electrochemical characteristics are achieved for
a three-layer system LSM2/{CGO-LSM1}/CGO sintered at 1410°C. The use of Ce-modified perovskites La 0.8Sr 0.2MnO 3 ± δ and La 0.6Sr 0.6CoO 3 ± δ as the collector layer of two-layer electrodes allows the electrochemical characteristics at moderately high temperatures
(600–750°C) to be improved. 相似文献
18.
Heat capacities of the Pb 2xSn 2(1-x)P 2Se 6 crystals ( x=0, 0.098, 0.251, 0.402 and 1.0) were measured using an adiabatic calorimeter at temperatures between 10 and 350 K. In the
crystal of x=0, two heat capacity anomalies corresponding to the ferroelectric commensurate - intermediate incommensurate(C-IC) phase
transition temperature T
i, and the incommensurate - paraelectric (IC-N) phase transition temperature T
c, were observed at 193.24±0.10 and 220.07±0.15 K, respectively. The phase transition temperatures decreased with an increase
in Pb 2+ concentration. The anomaly at Ti disappeared at x=0.251 in the mixed systems of the Pb 2xSn 2(1-x)P 2Se 6. In the crystal of Pb 2P 2Se 6 ( x=1.0), no phase transition was observed. The normal heat capacities for the mixed crystals were determined by least squares
fitting of the Debye and Einstein functions to the experimental data. The anomalous heat capacities gave the phase transition
entropies of 8.5 and 1.5 J mol -1 K -1 for x=0. The large transition entropies are consistent with an order-disorder mechanism in the ferroelectric-paraelectric phase
transitions in x=0.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
The Li 4+xM xSi 4+xO 4‐yLi 2O (M=Al, B; x = 0 to 0.6, y = 0 to 0.5) ion conductors were prepared by the Sol‐Gel method and examined in detail. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The experimental results show that the conductivity and sinterability in creased with the amount of excess lithium oxide in the silicate. The Li 2O phase acts as a flux to accelerate the sintering process and to obtain high conductivity of grain boundaries. The particle size of the sintered pellets is about 0.25 μm. The maximum conductivity at 200 °C is 5.40 × 10 ?3s cm ?1 for Li 4.4Al 0.4 Si 0.6O 4‐0.3Li 2O. 相似文献
20.
A powder X-ray diffraction experiment was performed on cubic Zr 1-xHf xW 2O 8 ( x=0.25, 0.50 and 0.75) solid solutions from 90 to 560 K. The lattice parameters of Zr 1-xHf xW 2O 8 at 121 K decreased linearly with increasing Hf contents, due to smaller ionic radius of hafnium than that of zirconium. Transition
temperatures due to α-β structural phase transition increased with increasing Hf contents, reflecting the decrease of lattice
free volume related to the orientation of unshared vertex of WO 4. Anomaly in the heat capacity of Zr 0.5Hf 0.5W 2O 8 was observed around 450 K which was 9 K lower than that by X-ray diffraction method. Transition entropy of Zr 0.5Hf 0.5W 2O 8 was 2.1 J mol -1 K -1, consistent with those of ZrW 2O 8 and HfW 2O 8. This consistent entropy supports that Zr 1-xHf xW 2O 8 ( x=0-1.0) has the same order-disorder phase transition mechanism.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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