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1.
A series of Ce xPr 1−xO 2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH 3OH and CH 4 on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO 2 was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO 2 crystal lattices. Raman bands at 465 and 1150 cm −1 in Ce xPr 1−xO 2−δ samples are attributed to the Raman active F 2g mode of CeO 2. The broad band at around 570 cm −1 in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm −1 may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr 6O 11 shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce xPr 1−xO 2−δ mixed oxides is lower than those of Pr 6O 11 or CeO 2. TPR results indicate that Ce xPr 1−xO 2−δ mixed oxides have higher redox properties because of the formation of Ce xPr 1−xO 2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH 3OH oxidation, while the activity of CH 4 oxidation is mostly related to reduction temperatures and redox properties. 相似文献
2.
Modern condensed-matter physics is increasingly concerned with the design, synthesis, analysis, and exploitation of chemically complex materials and structures. Complex metal oxides and strongly correlated electron systems such as YBa 2Cu 3O 7−x and La 1−xSr xMnO 3 are paradigmatic examples. Their production in the form of high-quality thin films is of both technological and fundamental importance and has stimulated a concerted effort in the last two decades to find and optimize efficient techniques to this end. This review discusses the physics behind and the requirements for synthesizing high-quality films of such materials and examines fundamental aspects of the growth processes associated with magnetron sputtering and pulsed laser deposition, the two techniques which presently offer the best solutions in this burgeoning field. 相似文献
3.
Structural peculiarities of Ce–Zr–La–O and Ce–Zr–La–O/Ru samples in mean of catalytic properties are compared. The samples (Ce:Zr = 1:1, La = 10÷30 mol.%, Ru = 1.5 wt.%) were obtained by sol–gel method (X-samples) and co-precipitation (P-samples). It is shown that Ce 0.45Zr 0.45La 0.1O 2−δ/Ru X-samples are characterized by high thermal stability and the highest catalytic activity in partial methane oxidation reaction. According to XRD, BET, FTIR, EPR and XPS data it is concluded that the difference in the samples catalytic activity is caused by various disposition of Ru-containing phase on the support surface. The distinction in the dimension of Ru-containing particles (3D or 2D) is conditioned by structural peculiarities of Ce 0.45Zr 0.45La 0.1O 2−δ and Ce 0.35Zr 0.35La 0.3O 2−δ P- and X-samples. 相似文献
4.
Dense ceramic mixed ionic and electronic conducting membranes have been deposited by atmospheric spray-pyrolysis technique onto porous ceramic substrates. Perovskite oxide layers, i.e. manganites La 1−xSr xMnO 3, ferrites La 1−xSr xFe 1−y(Co,Ni) yO 3, gallates La 1−xSr xGa 1−y(Co,Ni,Fe) yO 3, cobaltites La 1−xSr xCoO 3 and related perovskites such as lanthanum nickelate La 2NiO 4 layers have been prepared. The structure, morphology and composition of the layers were characterised by XRD, SEM and WDS, respectively. Density and gas tightness of the layers were studied as a function of deposition process parameters, film thickness (from 0.5 to 3 μm) and preparation procedure. The presence of cracks and defects due to thermo-mechanical stresses applied during or after the preparation process were correlated with the membrane composition and the corresponding thermal expansion coefficient differences between substrates and membranes. 相似文献
5.
In this communication, we report on the synthesis and characterization of a series of compounds with the general composition Ce 1−xSr xO 2−x (0.0≤ x≤1.0), to establish a detailed phase relation in the CeO 2–SrO system. The X-ray diffraction (XRD) pattern of the each product was refined to determine the solid solubility and the homogeneity range. The solid solubility limit of SrO in CeO 2 lattice, under the slow cooled conditions, is represented as Ce 0.91Sr 0.09O 1.91 (i.e. 9 mol% of SrO). A careful delineation of the phase boundary revealed that the stoichiometric SrCeO 3, in fact, contains a little amount of CeO 2 also. The mono-phasic compound could be obtained at the nominal composition Sr 0.55Ce 0.45O 1.45. The nominal composition Sr 2CeO 4, under the heat treatment used in the present investigation, was a bi-phasic mixture of SrCeO 3 and SrO. No new ordered phases were obtained in this system. 相似文献
6.
The electron-beam–sample interaction is analyzed using the standard theory for fast electrons in the accelerating energy range from 0.1 to 2 MeV when the sample to be observed with TEM is composed of different atoms. This theory allows taking into account the contribution of the nearest neighbors of the target atoms, which is a more real approximation. For direct interaction the normal expressions are obtained, but for the cascade phenomenon a better approximation is presented. This theory is applied to the analysis of the experimentally reported electron-beam-induced structure modification in the superconductor YBa 2Cu 3O 7−x, the quasicrystalline alloy Al 62Cu 20Co 15Si 3, and the tooth enamel hydroxyapatite. 相似文献
7.
Since the discovery of superconductivity in Sr 2CuO 2F 2+δ there has been an increased interest in ternary oxide-fluorides. Sr 2CuO 2F 2+δ is prepared via low temperature ( T = 220 °C) reaction routes. Low temperature fluorination induces an interesting structural rearrangement in the parent compound Sr 2CuO 3, which is a one-dimensional material containing linear chains of vertex sharing CuO 4 squares along the crystallographic b axis. Upon fluorination, one oxide is substituted by two fluorides and Cu 2+ becomes octahedrally coordinated by four oxides and two fluorides. The fluorinated compound Sr 2CuO 2F 2+δ displays the T-type structure (La 2CuO 4). Insertion of excess fluorine, δ, also takes place and this fluorine occupies interstitial sites in the T structure. Although the starting material Ca 2CuO 3 is isostructural to Sr 2CuO 3, Ca 2CuO 2F 2+δ displays the T′ (Nd 2CuO 4) structure due to the smaller radius of Ca 2+ compared to that of Sr 2+. The alkaline-earth palladates with the general formula A2PdO3 (A = Ba, Sr) are isostructural with the A2CuO3(A = Ca, Sr) materials. We prepared the Ba2−xSrxPdO3 (x = 0–2) series and performed low temperature fluorination, which led to the synthesis of the series Ba2−xSrxPdO2F2+δ (0 ≤ x ≤ 1.5). All the compounds in the Ba2−xSrxPdO2F2+δ series show T′ structure (Ca2CuO2F2+δ). Similarities and differences with Sr2CuO2F2+δ and Ca2CuO2F2+δ will be discussed. 相似文献
8.
The oxygen permeation properties of mixed-conducting ceramics SrFeCo 0.5O 3−δ (SFCO), Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCFO), La 0.2Sr 0.8Co 0.8Fe 0.2O 3−δ (LSCFO) and Ba 0.95Ca 0.05Co 0.8Fe 0.2O 3−δ (BCCFO) were studied by thermogravimetric method in the temperature range 600–900 °C. The results show that the oxygen adsorption rate constants ka of all material are larger than oxygen desorption rate constants kd and both ka and kd are not strongly dependent on temperature in the studied temperature range. The oxygen vacancy contents δ(N 2) and δ(O 2) in nitrogen and oxygen and their difference Δ δ = δ(N 2) − δ(O 2) play an important role in determining the temperature behavior of oxygen permeation flux JO2. 相似文献
9.
The primary crystallization field of a perovskite solid solution Bi 1−xSr xMnO 3−δ was delimited by calculating the respective phase equilibria in the quaternary Bi–Sr–Mn–O system. The calculations are based on the recent assessment involving all three ternary subsystems, a quaternary liquid approximated as a mixture of Mn, MnO, Mn 2O 3, SrO and Bi 2O 3 species with binary Redlich–Kister coefficients and the perovskite phase described in terms of a point defect model allowing Sr 2+ for Bi 3+ substitution, oxygen vacancy formation and the related Mn 3+/Mn 4+ mixing on Mn-sublattice. The crystallization path and the composition of the crystallized solid solution are compared with single crystal growth experiments performed by self-flux method from a Bi-rich melt. The crystallization path obtained for a selected feed composition for which the largest and high quality single crystal have been grown, turns out to end very close to the global eutectic point. 相似文献
10.
Phase equilibria in the LaFeO 3–“LaNiO 3” were studied at 1100 °C in air. The samples were synthesized by standard ceramic and/or solution route via nitrate or citrate precursors. According to the results of XRD it was found that the homogeneity ranges of LaFe 1−xNi xO 3−δ solid solution lay within 0.0 ≤ x ≤ 0.4 (sp.gr. Pbnm) and 0.6 ≤ x ≤ 0.8 (sp.gr. ). The structural parameters (bond lengths, atom coordinates) for the single-phase samples were refined using Rietveld analysis. The unit cell parameters versus LaFe 1−xNi xO 3−δ composition are presented. 相似文献
11.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
12.
Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C 5H 5)Fe(C 5H 4)] can be prepared by oxidation of acylferrocenes FcCOCH 2R or, more efficiently, by oxidation of the isomeric ketones FcCH 2COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH 2PPh 3) +I − via the acylated salts [FcCH(COR)PPh 3] +I −. The haloacylferocenes FcCOCCl x H 3−x ( x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel—Crafts acylation of ferrocene using CCl xH 3−xCOCl/AlCl 3, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCCl xH 3−x and the other giving the reduced products FcCOCCl x−1H 4−x. Two diketones FcCOCOFc 3b and FcCOCOC 6H 4Ph 3c have been structurally characterised by single-crystal X-ray diffraction. 相似文献
13.
CrO x/La 2O 3 mixed oxides, prepared by impregnating La 2O 3 with appropriate aqueous solutions of (NH 4) 2CrO 4 and calcining at 600 °C for 4 h, have been investigated by means of XRD, TPR, XPS, DRIFTS, and Raman spectroscopy (RS). The formation of the compounds La 2CrO 6, La(OH)CrO 4 and LaCrO 4 under these conditions was evidenced. Strong peaks at 864, 884, 913, and 921 cm −1, as well as weak peaks at 136, 180, 354, 370, and 388 cm −1 in the RS spectrum of CrO x/La 2O 3 have been assigned to La 2CrO 6. 相似文献
14.
Perovskite-type oxides of the series La 1−xA xMn 1−yB yO 3 (A = Sr; B = Fe or Co) were prepared by solution combustion synthesis and characterized by X-ray diffraction, specific surface analysis, transmission electron microscopy and field emission scanning electron microscopy techniques. Their activity towards the combustion of methane was evaluated in a temperature programmed combustion microreactor. The LaMn 0.9Fe 0.1O 3 catalyst was found to provide the best performance. The half-conversion temperature of methane over the LaMn 0.9Fe 0.1O 3 catalyst was 398 °C with a W/ F = 0.12 g s/cm 3 and a methane feed concentration of 0.4 vol% under oxygen excess. Via temperature programmed oxygen desorption (TPD) analysis as well as catalytic combustion runs, the prevalent activity of the LaMn 0.9Fe 0.1O 3 catalyst could be explained by its higher and increased capability to desorb suprafacial, weakly chemisorbed oxygen species. Further catalyst development allowed to maximise the catalytic activity of this compound by promoting it with CeO 2 (1:1 molar ratio) and with 1 wt% Pd. This promoted catalyst was lined on cordierite monoliths in a γ-Al 2O 3-supported form (catalyst weight percentage: 15 wt%) and then tested in a lab-scale test rig under realistic conditions for compressed natural gas-vehicles' exhaust gas treatment. Half methane conversion was achieved at 340 °C (gas high space velocity = 10 000 h −1), nearly the same but with a fourfold lower amount of the expensive noble metal than that used in commercial 4wt%Pd–γ-Al 2O 3 catalysts. 相似文献
15.
Hydrated strontium borate, SrB 4O 7·3H 2O, has been synthesized and characterized by XRD, FT-IR, DTA-TG and chemical analysis. The molar enthalpy of solution of SrB 4O 7·3H 2O in 1 mol dm −3 HCl(aq) was measured to be (21.15 ± 0.29) kJ mol −1. With incorporation of the previously determined enthalpies of solution of Sr(OH) 2·8H 2O(s) in [HCl(aq) + H 3BO 3(aq)] and H 3BO 3 in HCl(aq), and the enthalpies of formation of H 2O(l), Sr(OH) 2·8H 2O(s) and H 3BO 3(s), the enthalpy of formation of SrB 4O 7·3H 2O was found to be −(4286.7 ± 3.3) kJ mol −1. 相似文献
16.
Polycrystalline samples of Cu 2+xTa 4O 12+δ were prepared by solid-state reactions. Copper tantalate shows a remarkable compositional flexibility with respect to both the copper and oxygen stoichiometry. Single phase compounds could be synthesised for 0.125 ≤ x ≤ 0.5. Slowly cooled samples are green and possess a pseudo-tetragonal unit cell, which changes to a pseudo-cubic symmetry for x ≥ 0.45. Rapidly cooled aliquots are brown and have a (pseudo-) cubic structure. For both the slow-cooled and quenched samples a linear increase of the oxygen content with x was observed, the values of δ for the latter being significantly smaller. Magnetic measurements reveal a ferrimagnetic transition at 12.5 K, the strength of which is strongly reduced both by increasing the copper content and by quenching. 相似文献
17.
The growth of REBa 2Cu 3O 7−δ (REBCO = rare earth elements) high-temperature superconducting thick films by liquid phase epitaxy is reviewed, which are most promising for electronic device and coated conductor applications. The paper focused on thermodynamic relations, chemical reactions and physical phenomena in the liquid phase epitaxy process, which are closely related to the control of the microstructures and properties of materials. Recent progresses achieved and the problems to be solved have been reviewed in above sections. 相似文献
18.
The 127I NQR, IR absorption and Raman spectra of impurity-doped and mixed lithium iodate Li 1−xH xIO 3 crystals grown from water solutions with different LiIO 3/HIO 3 ratios were investigated depending on the content of the impurity hydrogen x. The NQR results suggested that, at small concentration of doping iodic acid x<0.22, the lattice dynamics of the crystal grown from water solution changes significantly though the crystal retains hexagonal symmetry. Spectroscopic studies are compatible with average hexagonal symmetry of the grown doped crystals. From the results of Raman studies at room temperature and 100 K, the concentration range of hydrogen dopant 0.22< x<0.36 was found where disordered solid solution crystals Li 1−xH xIO 3 are formed. 相似文献
19.
Reactions between thiomolybdate or thiotungstate [Et 4N] 2[MS 4] (M = Mo, W) and CuSBu t led to the formation of two novel Mo(W)/Cu/S clusters [Et 4N] 4[{MS 4Cu 2(μ-SBu t)} 4] (1, M = Mo; 2, M = W). Single-crystal X-ray diffraction studies reveal that 2 is the first example of a molecular square containing CuS 2WS 2Cu building blocks. The reactions of [Et 4N] 2[MS 4] with CuCl followed by the addition of K 2SSS (SSS = 1,3,4-thiadiazole-2,5-dithiolate) yielded novel polymers {[Et 4N] 2[MS 4Cu 2(SSS)]} n (3, M = Mo; 4, M = W). Crystal structure determination shows that the CuS 2WS 2Cu building blocks in the anion of 4 are bridged by SSS 2− ligands to produce a helical chain running down the crystallographic b axis. 相似文献
20.
We performed a study on the dielectric properties of Ba xSr 1−xTiO 3–Mg 0.9Zn 0.1O (BST–MZO) composite ceramics derived from core–shell structured nanopowders with the shell of zinc doped MgO and core of Ba xSr 1−xTiO 3. It was found that the ceramics exhibit a significant improvement in dielectric response under a DC electric field. The Curie temperature decreases more significantly in the BST–MZO composite ceramics compared to that of pure BST ceramics. The tunability of Ba 0.75Sr 0.25TiO 3–40%MZO is 23.49% at 20 °C. The dielectric properties at high frequency also show low dielectric constant and great reduction in dielectric loss. These ceramics are expected to be useful in microwave devices. 相似文献
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