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1.
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
2.
A composite of oxygen ion conducting oxide Ce 0.8Sm 0.2O 2−δ (60 vol.%) and electron conducting oxide La 0.8Sr 0.2CrO 3−δ was prepared by sintering a powder compact at a temperature of 1550 °C. No significant reaction between the two constituent oxides was observed under preparation and oxygen permeation conditions. Appreciable oxygen permeation fluxes through the composite membrane were measured at elevated temperatures with one side of it exposed to the ambient air and the other side to a flowing helium gas stream. The oxygen flux initially increased with time, and took a long time to reach a steady value. A steady oxygen permeation flux as high as 1.4 × 10 −7 mol cm −2 s −1 was obtained with a 0.3 mm thick membrane at 950 °C under a relatively small oxygen partial pressure difference of 0.21 bar/0.0092 bar. It was revealed that the overall oxygen permeation process was mainly limited by the transport in the bulk of the membrane in the range of the membrane thickness greater than 1.0 mm, and the limitation by the surface oxygen exchange came into play at reduced thickness of 0.6 mm. 相似文献
3.
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
4.
In this article, the phase compositions, thermal, mechanical and transport properties of both the SrCo 0.8Fe 0.2O 3−δ (SCF) and the SrCo 0.8Fe 0.1Sn 0.1O 3−δ (SSCF) ceramic membranes were investigated systematically. As compared with the SCF membrane, the SSCF one had a more promoted thermal shock resistance, which related to its small thermal expansion coefficient between them and an enhanced composite structure for it. For the SCF membrane, a permeation rate of 1.9 × 10 −6 mol cm −2 s −1 was obtained at 1000 °C and under the oxygen partial pressure gradient of PO2 (h)/ PO2 (l) = 0.209 atm/0.012 atm; however, the permeation rate was 2.5 × 10 −6 mol cm −2 s −1 for the SSCF one in the same measuring condition. In addition, both peak values of total electrical conductivity ( σe) for SSCF sample appeared with increasing temperature. The second peak value of σe for SSCF one was regarded as the contribution from its minor phase, which appeared with the mixed conducting behavior resulting from partly Co-dissolving into its lattice. 相似文献
5.
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
6.
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
7.
The samples of La 0.4Sr 0.6Co 1−yFe yO 3−δ ( y = 0.2 and 0.4) were prepared using both conventional ceramic technique and nitrate–citrate precursors technique. The phase identification was made by X-ray diffraction method. The refinement of structural parameters from the XRD and neutron diffraction measurements was performed by full profile Rietveld analysis. Neutron diffraction showed that both samples possess distorted perovskite-type structure. Oxygen nonstoichiometry was measured by chemical analysis and thermogravimetry (TG) analysis in the range 20 ≤ T/°C ≤ 900 and 2E-5 ≤ pO 2/atm ≤ 4E-1. TG-experiments indicate a relatively fast and reversible oxygen exchange at pO 2 > 1E-2 atm. Mass saturation occurs at T < 300 °C upon cooling. The absolute value of oxygen nonstoichiometry was determined by iodometric titration measurements. It was found that both samples have practically stoichiometric composition at 300 °C in air and δ increases with increasing temperature and decreasing oxygen partial pressure. 相似文献
8.
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
9.
Powder X-ray diffraction, 119Sn NMR spectra, and 1H NMR spin–lattice relaxation times, T1, were measured for (CH 3) nNH 4−nSnCl 3 ( n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of 1H T1 was analyzed in terms of the CH 3 reorientation and other motions of the whole cation. Except for the phase transition in CH 3NH 3SnCl 3, which is from monoclinic to rhombohedral at 331 K, 1H T1 was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl 3] nn− perovskite lattice. 相似文献
10.
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
11.
The dependence of the integral enthalpy of hydrogenation (or dehydrogenation) of the intermetallic compounds (IMCs) Ce xLa 1−xNi 5 ( x = 0, 0.05, 0.1 or 0.3) on pressure in the range 0.5–6 MPa was studied by the method of differential scanning calorimetry. It has been shown that at x = 0 and x = 0.05 the absorption (or desorption) proceeds via the formation of a stable intermediate hydride phase. 相似文献
12.
The oxygen separation membrane having perovskite structure for the partial oxidation of methane to synthesis gas was prepared. La 0.7Sr 0.3Ga 0.6Fe 0.4O 3−δ (LSGF) perovskite membrane coated with La 0.6Sr 0.4CoO 3−δ (LSC) (M1), and the one side of M1 membrane coated with NiO (M2) was prepared to examine the partial oxidation of methane. The single oxygen permeations of the LSC + LSGF (M1) membrane and NiO coated membrane (M2) were measured. The oxygen permeation flux in M1 membrane was higher than that of M1 membrane at 850 °C. The partial oxidation experiment of methane using the prepared membranes was examined at 850 °C. The value of CH4 conversion and CO selectivity of M2 membrane was higher than that of M1 membrane. NiO/NiAl2O4 catalyst was used to improve the methane conversion, and the partial oxidation experiment of methane with M1 membrane was examined at 850 °C. The CH4 conversion was 88%, and CO selectivity was 100%. 相似文献
13.
Synthesis of the Y xGd 1−xBa 2Cu 4O 8 phases ( x=1; 0.5; 0.75) by special method from nitrates is described in this paper. Dissolution enthalpies of YBa 2Cu 4O 8, Y 0.5Gd 0.5Ba 2Cu 4O 8, Y 0.75Gd 0.25Ba 2Cu 4O 8, Y 2O 3, Gd 2O 3, CuO, BaCO 3 were measured in 6 N HCl at 323 K. On the basis of obtained experimental data, the enthalpies of some reactions with Y xGd 1−xBa 2Cu 4O 8 were determined. It was established that the above-mentioned 1 : 2 : 4 superconductors were thermodynamically more favourable than mixtures including CuO, YBa 2Cu 3O x. It was also established that, according to the obtained data, these phases can react with CO 2. 相似文献
14.
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
15.
An overview on the variation of the thermal expansion, the electrical conductivity as well as non-stoichiometry of the oxide content as a function of composition within the quasi-ternary system La 0.8Sr 0.2MnO 3−δ–La 0.8Sr 0.2CoO 3−δ–La 0.8Sr 0.2FeO 3−δ in air is presented. The various powders were synthesized under identical conditions. The DC electrical conductivity values of the compositions at 800 °C in air vary in a wide range from 15 to 1338 S cm −1. The magnitude of electrical conductivity of the perovskites is mainly determined by the percentage of cobalt in the compositions. A similar behaviour was observed for the measured thermal expansion coefficients between room temperature and 1000 °C in air, increasing from 10.9 to 19.4 × 10 −6 K −1 as a function of cobalt content. Changes in the oxygen stoichiometry of the materials were characterized by temperature-programmed oxidation measurements. 相似文献
16.
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
17.
The matrix isolation technique has been combined with theoretical calculations to identify and characterize the photoproducts in the reactions of CH 3CN with CrCl 2O 2 and OVCl 3. Twin jet co-deposition of these reagents led to the formation of a 1:1 molecular complex which was observed using UV/visible spectroscopy. Irradiation of these matrices with light of λ>300 nm led to the observation of new bands in the infrared spectra, the most intense of which was seen at 1942 cm −1 for the CrCl 2O 2/CH 3CN system. The product bands are assigned to the 2η complexes of acetonitrile n-oxide with CrCl 2O and VCl 3, respectively. Identification of these species was supported by extensive isotopic labeling ( 2H and 15N), as well as by B3LYP/6-311++G(d,2p) density functional calculations. 相似文献
18.
Reactions of CpMoIr 3( μ-CO) 3(CO) 8 (1) with stoichiometric amounts of phosphines afford the substitution products CpMoIr 3( μ-CO) 3(CO) 8−x (L) x (L = PPh 3, x = 1 (2), 2 (3); L = PMe 3, x = 1 (4), 2 (5), 3 (6)) in fair to good yields (23–54%); the yields of both 3 and 6 are increased on reacting 1 with excess phosphine. Products 2–5 are fluxional in solution, with the interconverting isomers resolvable at low temperatures. A structural study of one isomer of 2 reveals that the three edges of an MoIr 2 face of the tetrahedral core are spanned by bridging carbonyls, and that the iridium-bound triphenyiphosphine ligates radially and the molybdenum-bound cyclopentadienyl coordinates axially with respect to this Molr 2 face. Information from this crystal structure, 31P NMR data (both solution and solid-state), and results with analogous tungsten—triiridium and tetrairidium clusters have been employed to suggest coordination geometries for the isomeric derivatives. 相似文献
19.
The H 2O 2-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu 4nN] 4[Pr 2iNH 3] 2H[P{Ti(O 2)} 2W 10O 38]·H 2O (1) (with two η 2-peroxotitanium sites in the anion) has been studied in search of the catalytically active species involved. 31P NMR spectra of 1, measured under a variety of conditions, revealed that the active species was not hydroperoxotitanium complex [P{Ti(OOH)} 2W 10O 38] 7−or [P{Ti(OOH)}Ti(O 2)W 10O 38] 7−. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H 2O 2] dependence). It was concluded that the net catalytic reaction for the epoxidation occurred through the two-electron oxidation at the hydroperoxotitanium site in the catalyst. 相似文献
20.
The excess molar enthalpies ( ) for the binary mixtures of trimethyl phosphate (TMP) with alkanols {CH 3(CH 2) nOH, n = 0–3} have been measured with an isothermal calorimeter at 298.15 K and atmospheric pressure. The values are positive for all the mixtures over the whole composition range. The values increase in the order methanol < ethanol < 1-propanol < 1-butanol. The experimental results have been correlated with the Redlich–Kister equation. 相似文献
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