共查询到20条相似文献,搜索用时 46 毫秒
1.
Syed M. BukhariJavier B. Giorgi 《Solid State Ionics》2011,194(1):33-40
A new series of perovskite materials with formula Sm0.95Ce0.05Fe1 − xNixO3 − δ (0 ≤ x ≤ 0.10) has been prepared by sol-gel combustion via a citrate precursor route. X-ray diffraction data showed that materials prepared by this method had a single orthorhombic phase belonging to the Pnma (62) space group. The study of powders sintered in air and in reducing atmospheres reveals that these materials do not show phase separation in air (up to 1350 °C) nor under 5% v/v H2/N2 (up to 700 °C), but a phase separation of Sm2O3 does occur at and above 800 °C under 5% v/v H2/N2 without deterioration of the perovskite phase. The surfaces of all the powders (fresh, in-situ reduced and ex-situ reduced) were Sm rich, and multiple oxidation states for Fe were observed. XP analysis of in-situ reduced samples (800 °C and above) shows that metallic Fe forms in all nickel doped materials except x = 0.07. The surface oxygen vacancies and percentages of lattice and adsorbed oxygen for this series of Ni doped materials were determined and the oxygen recapturing ability is explained in terms of the multiple oxidation states of Fe. 相似文献
2.
The atomic-scale structural changes in an α-Fe2O3 (hematite) (0 0 0 1) surface induced by sulfidation and subsequent oxidation processes were studied by X-ray photoemission spectroscopy, LEED, and X-ray standing wave (XSW) measurements. Annealing the α-Fe2O3(0 0 0 1) with a H2S partial pressure of 1 × 10−7 Torr produced iron sulfides on the surface as the sulfur atoms reacted with the substrate Fe ions. The oxidation state of the substrate Fe changed from 3+ to 2+ as a result of the sulfidation. The XSW measured distance of the sulfur atomic-layer from the unrelaxed substrate oxygen layer was 3.16 Å. The sulfide phase consisted of three surface domains identified by LEED. Formation of the two-dimensional FeS2 phase with structural parameters consistent with an outermost layer of (1 1 1) pyrite has been proposed. Atomic oxygen exposure oxidized the surface sulfide to a sulfate () and regenerated the α-Fe2O3(0 0 0 1) substrate, which was indicated by a (1 × 1) LEED pattern and the re-oxidization of Fe to 3+. 相似文献
3.
Andrew B. Helms 《Surface science》2009,603(22):3262-1561
The chemical compound 2,4-pentanedione (Hacac) has been shown to etch the oxidized metal surfaces metals such as copper and nickel, but not their unoxidized surfaces. Here it is shown that on the γ-Al2O3/NiAl (1 0 0) surface (oxidized NiAl (1 0 0)) etching of aluminum occurs at 170 K and 750 K. Reflection-absorption infrared spectroscopy (RAIRS) is used to show that Hacac binds to both the clean, metallic and oxidized surfaces, but decomposition and combustion products dominate on the metallic surface and no etching occurs. The binding process that involves a deprotonation reaction of the enol species was identified by redshift in the carbonyl peaks and the appearance of an Al-H peak observed in the IR spectrum. The implication of these results is that there is both an unusual low temperature and high temperature etching of the alumina by bound acac. 相似文献
4.
L. DeleebeeckV. Birss 《Solid State Ionics》2011,203(1):69-79
Sr-doped and Sr-free La1 − xSrxMn1 − yCryO3 ± δ (LSMC, x(Sr) = 0-0.2, y(Cr) = 0.4-0.6) perovskite-type oxides were synthesized and evaluated as single phase anodes for use in intermediate temperature solid oxide fuel cell applications. Their thermo-chemical and chemical stabilities were investigated in hydrogen at high temperatures and correlated with their oxygen non-stoichiometry (3 ± δ), determined by permanganate titration. The catalytic activity towards hydrogen oxidation was examined as a function of oxide sintering time, operating temperature, and the Sr and Cr contents, using a Pt mesh current collector. While all of the perovskite oxides studied here showed some irreversible performance degradation with time under both open circuit and anodically polarized conditions, La0.9Sr0.1Mn0.6Cr0.4O3.03 (LSMC9164), sintered at 1200 °C for 10 h, was found to be the most catalytically active and also the most stable. 相似文献
5.
Recent experimental evidence calls for a reinterpretation of the oxidized structure in chemically distinct domains of the hematite (0 0 0 1) surface as the ferryl (FeO) termination rather than the bulk terminated O3-Fe-Fe-R structure. Although this interpretation is consistent with experimental data and ab initio thermodynamics calculations, it raises serious questions about how molecular oxygen can be dissociated on a surface where reactive iron centers are slightly more than 5 Å apart. Here, we propose a novel cooperative bimolecular mechanism that provides a reasonable pathway for the formation of the unusual ferryl surface termination and should be readily reversible, which is important for understanding the function of hematite surfaces as an oxidation catalyst. 相似文献
6.
SrFeO3 − δ compound is prepared by the thermal decomposition method followed by ball milling. Analysis of Mössbauer spectrum and X-ray diffraction study proves the presence of multi-phase nature, i.e., Sr8Fe8O23 and Sr4Fe4O11 phases at room temperature. Furthermore, the Mössbauer spectrum at room temperature evidenced the presence of major Fe3.5+ which is the resultant of equal contributions of Fe4+ and Fe3+. The Nyquist plot at all measured temperatures (80–230 K) suggests that the dielectric response is well associated with single relaxation time (exponential parameter, n∼1) i.e., the Debye-type. Modulus analysis exhibits the non-universal dielectric behaviour (stretched exponential parameter, β>1) below 230 K and the Debye-type responds (β∼1) at and above 230 K. The Debye-type behaviour exhibited by SrFeO2.81 at around room temperature in its defect state offers a new opening for this material for multifunctional applications. 相似文献
7.
Xianjin Feng Fan Yang Feng Ji Fujian Zong Caina Luan Honglei Ma 《Applied Surface Science》2008,254(20):6601-6604
Antimony-doped tin oxide (SnO2:Sb) single crystalline films have been prepared on α-Al2O3 (0 0 0 1) substrates by metal organic chemical vapor deposition (MOCVD). The antimony doping was varied from 2% to 7% (atomic ratio). Post-deposition annealing of the SnO2:Sb films was carried out at 700-1100 °C for 30 min in atmosphere ambient. The effect of annealing on the structural, electrical and optical properties of the films was investigated in detail. All the SnO2:Sb films had good thermal stability under 900 °C, and the 5% Sb-doped SnO2 film exhibited the best opto-electrical properties. Annealed above 900 °C, the 7% Sb-doped SnO2 film still kept high thermal stability and showed good electrical and optical properties even at 1100 °C. 相似文献
8.
Structural and photoluminescence properties of SnO2:Ga films deposited on α-Al2O3 (0 0 0 1) by MOCVD
Xuan Pei Jin Ma Ti Ning Zhenguo Song Yongliang Tan Caina Luan 《Journal of luminescence》2010,130(7):1189-1193
Gallium-doped tin oxide (SnO2:Ga) films have been prepared on α-Al2O3 (0 0 0 1) substrates at 500 °C by the pulse mode metalorganic chemical vapor deposition (MOCVD) method. The relative amount of Ga (Ga/(Ga+Sn) atomic ratio) varied from 3% to 15%. Post-deposition annealing of the films was carried out at different temperatures for 1.5 h in ambient atmosphere . The structural, electrical, optical and photoluminescence (PL) properties of the films have been investigated as a function of annealing temperature. All the films have the rutile structure of pure SnO2 with a strong (2 0 0) preferred orientation. A single ultraviolet (UV) PL peak near 337.83 nm was observed at room temperature for the 3% Ga-doped as-grown film and near 336 nm for the 15%-doped film, which can be ascribed to electron transition from the oxygen vacancy and interstitial Ga3+ donor levels to the acceptor level formed by the substitution of Ga3+ for the Sn site. After annealing, the luminescence spectra have changed a little bit, which is being discussed in detail. 相似文献
9.
The high-resolution infrared spectrum of deuterated fluoroform (DCF3) was studied in the 700 and 1200 cm−1 regions, with the aim of assigning and analyzing the ν4 CF3 asymmetric stretching vibration. The Fermi-type anharmonic coupling between the ν4 = 1 and ν3 = ν6 = 1 rovibrational levels, already mentioned in an early work of Ruoff et al. [Spectrochimica Acta Part A 31A (1975) 1099-1100], was studied here for the first time under high resolution. Assignments in the ν3 + ν6/ν4 band system were confirmed and extended by the identification of the ν3 + ν6 − ν6 and ν4-ν6 bands in the 700 cm−1 region, the latter being enhanced near the Fermi crossings of the studied levels. Data from both the hot and difference bands were included in the analysis. The close separation of the studied vibrational levels of about 14.8 cm−1 produces a large variety of resonance crossings which involve levels with . Besides the Fermi () and Coriolis () resonances, they were accounted for by inclusion of additional higher-order ( and ) interaction terms between the vibrational states. The least-squares fit of more that 16,000 vibration-rotation transitions provides a quantitative reproduction of data in all bands. 相似文献
10.
YSr2Fe3O8 − δ was prepared by traditional solid state reaction method and characterized by X-ray diffraction, ac impedance, dc conductivity, dilatometry and thermogravimetric analysis for possible use in solid oxide fuel cells (SOFCs). YSr2Fe3O8 − δ crystallizes with tetragonal symmetry in the space group P4/mmm and found to be stable at high temperatures under H2 and air. Four probe dc electrical conductivity measurements show that the conductivity increases up to 745 K and then decreases with temperature; the highest conductivity σ745K = 43.5 S cm− 1. The n-type conductivity at low oxygen partial pressure (pO2) changes to p-type at high pO2. Polarization behavior was investigated measuring the ac impedance response in symmetrical cell arrangements in air with YSZ and GDC electrolytes. Cathodic area specific resistance (ASR) varies with firing temperature. The lowest area specific resistance was observed with a GDC electrolyte fired at 1000 °C. In case of YSZ, ASR increases and in case of GDC, ASR decreases in air when electrode firing temperature decreases. At 800 °C ASRs are 0.20 Ω cm2 and 0.65 Ω cm2 with GDC and YSZ electrolytes, respectively, in air. Fuel cell measurements with symmetrical electrodes were performed using a thin YSZ electrolyte under H2 at anode and air at cathode, show that the power density is about 0.035 W/cm2 at 900 °C. 相似文献
11.
Douglas T. Petkie Paul Helminger Frank C. De Lucia 《Journal of Molecular Spectroscopy》2010,261(2):129-135
The analysis of the rotational spectrum of HNO3 has been extended to include the υ8 = υ9 = 1 state at 1205.7 cm−1 and the υ6 = υ7 = 1 state at 1223.4 cm−1. Based on 78-519 GHz data, the assignments in the 8191 vibrational state have been significantly expanded from the previously reported microwave measurements [T.M. Goyette, F.C. De Lucia, J. Mol. Spectrosc. 139 (1990) 241-243]. A new microwave analysis is also reported for the 6171 vibrational state. A simultaneous analysis takes into account the localized ΔKa = ±2 Fermi resonances between the vibrational states, describes the torsional splitting of 3.3 and 1.4 MHz for the 8191 and 6171 states respectively, and fits to experimental accuracy over 1500 rotational transition frequencies that extend up to J = 59. Infrared energy levels [A. Perrin, J.-M. Flaud, F. Keller, A. Goldman, R. D. Blatherwick, F. J. Murcray, C. P. Rinsland, J. Mol. Spectrosc. 194 (1999) 113-123] were also included in the analysis and fit to experimental accuracy. Measurement of strongly perturbed transitions in each vibrational state provide a determination of the band origin difference of 17.733184(17) cm−1. The rotational constants agree well with those predicted by vibrational-rotational constants of the fundamental modes. Furthermore, the analysis will provide a very accurate simulation of the infrared spectrum of HNO3 in the 8.3 μm region. 相似文献
12.
Sn-doped Ga1.4In0.6O3 films have been prepared on α-Al2O3 (0 0 0 1) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The Sn-doping was varied from 0% to 7% (atomic ratio). Polycrystalline films with resistivity of 4.9 × 10−3Ω cm, carrier concentration of 5.9 × 1019 cm−3 and Hall mobility of 21.4 cm2 v−1 s−1 was obtained at 5 at.% of Sn concentration. The average transmittance for the Sn-doped Ga1.4In0.6O3 films in the visible range was over 90%. The bandgap of the films varies from 3.85 to 4.21 eV. 相似文献
13.
Clay M. Horiuchi 《Surface science》2010,604(2):98-1297
The adsorption and thermal chemistry of γ-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts of CO2 are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO2, and H2. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism. 相似文献
14.
Surinderjit Singh BhellaVenkataraman Thangadurai 《Solid State Ionics》2011,192(1):229-234
In this paper, we report the synthesis, crystal structure and electrical transport properties of new K-doped Ba3CaNb2O9 (BCN) and investigate their chemical stability in H2O and pure CO2 at elevated temperature. The powder X-ray diffraction (PXRD) of Ba2.5K0.5CaNb2O9 − δ, Ba2.25K0.75CaNb2O9 − δ, Ba2KCaNb2O9 − δ, and Ba1.75K1.25CaNb2O9 − δ showed the formation of a single-phase double perovskite (A3BB/2O9)-like cell with a lattice constant of a ∼ 2ap (where ap is a simple perovskite cell of ∼ 4 Å). Perovskite-like structure was found to be retained after treating with CO2 at 700 °C and also after boiling H2O for 120 h. The lattice constant of CO2 and H2O treated samples was found to be comparable to that of the corresponding as-prepared compound. The total electrical conductivity of all the investigated K-doped BCN increases with increasing K content in BCN in various atmospheres, including air, dry H2, wet N2 and wet H2. The electrical conductivity in dry and wet H2 atmospheres was found to be higher than that of air in the temperature range of 300-700 °C, while in wet N2 a slightly lower value was observed. Among the compounds investigated in the present study Ba1.75K1.25CaNb2O9 − δ showed the highest total electrical conductivity of 1 × 10− 3 S/cm in dry H2 at 700 °C with an activation energy of 1.28 eV in the temperature range of 300-700 °C. 相似文献
15.
Ga2(1−x)In2xO3 thin films with different indium content x [In/(Ga + In) atomic ratio] were prepared on α-Al2O3 (0 0 0 1) substrates by the metal organic chemical vapor deposition (MOCVD). The structural and optical properties of the Ga2(1−x)In2xO3 films were investigated in detail. Microstructure analysis revealed that the film deposited with composition x = 0.2 was polycrystalline structure and the sample prepared with x up to 0.8 exhibited single crystalline structure of In2O3. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The average transmittance for the films in the visible range was over 90%. 相似文献
16.
Hai Hua Tang 《Surface science》2007,601(16):3293-3302
The interaction of ethyl vinyl ketone (EVK) with Si(1 1 1)-7 × 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The disappearance of both stretching vibrations of CH2 (3099 cm−1) and CO (1684 cm−1) coupled with the appearance of new CC stretching mode (1660 cm−1) in the HREELS spectra of chemisorbed EVK clearly demonstrates the direct involvement of conjugated CC and CO bonds to form a SiC1H2C2HC3(C4H2C5H3)OSi surface species via [4 + 2]-like cycloaddition in a highly selective manner. In addition, XPS studies show that the C1s binding energies of C1/C2 and C3 upon chemisorption display chemical downshifts of 0.8 eV and 2.2 eV, respectively, further confirming the proposed [4 + 2]-like cycloaddition reaction for the EVK/Si(1 1 1)-7 × 7 system. DFT theoretical calculations suggest that the proposed [4 + 2]-like cycloadduct is thermodynamically most favorable. 相似文献
17.
The phase stability, thermal expansion, electrical conductivity, and oxygen permeation of perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1 − xNbxO3 − δ (x = 0 − 0.2) have been investigated. Room-temperature X-ray diffraction of as-prepared powders indicates that in the investigated compositional range solid solutions are formed. Long-term annealing experiments both in flowing air and nitrogen, at 750 °C, demonstrate that the phase instability observed in parent Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) is suppressed already at the minimum substitution of 5 mol% of niobium for (Co, Fe). Both electrical conductivity and thermal expansion are found to decrease with increasing niobium concentration, which behaviors can be explained by defect chemical considerations, taking into account charge compensation mechanisms by doping BSCF with Nb5+ donor cations. The oxygen permeation flux of 10 mol% Nb-substituted BSCF, in the range 800-900 °C, is reduced by 10% relative to that found for parent BSCF. Switching from helium to a CO2-containing purge gas results in a severe reduction or cessation of the oxygen flux. Options are discussed to avoid undesired formation of surface carbonates. 相似文献
18.
19.
D.A. BelovA.V. Shlyakhtina S.Yu. StefanovichA.N. Shchegolikhin A.V. KnotkoO.K. Karyagina L.G. Shcherbakova 《Solid State Ionics》2011,192(1):188-194
Low-temperature ordering transitions in polycrystalline high temperature conductors (Dy1 − xCax)2Ti2O7 − δ (x = 0, 0.1) prepared using co-precipitation, mechanical activation and solid-state reactions at 1400 or 1600 °C have been studied by impedance spectroscopy at low frequencies and thermal mechanical analysis (TMA). The dielectric permittivity and loss tangent of the ceramics obtained have been measured as a function of temperature at low frequencies (0.5−500 Hz). The results provide evidence for the relaxation of point defects, most likely oxygen vacancies, at 500−600 °C and an antiferroelectric low-temperature phase transition of the second order, associated with re-arrangement process in the oxygen sublattice of pyrochlore structure. The temperature of the antiferroelectric transition is 700 to 800 °C, depending on the synthesis procedure and ceramic composition. Calcium doping of Dy2Ti2O7 leads to the formation of additional oxygen vacancies and, in the case of the samples prepared via co-precipitation, increases the peaks in permittivity due to the relaxation process and ordering transition by three or six times, respectively. 相似文献
20.
The growth processes and structures of Fe/Si(1 1 1) ultrathin films grown by solid-phase reactive epitaxy were investigated by coaxial impact-collision ion scattering spectroscopy (CAICISS). It has been revealed that the Fe(1 1 1) thin films with a bcc-type structure were epitaxially grown on a Si(1 1 1) crystal, even at room temperature, and formed a single-domain structure: Fe(1 1 1)∥Si(1 1 1). After annealing at above 600 °C, the Fe(1 1 1) films were transformed into β-FeSi2 via the collapse of the bcc-type structure to an amorphous or polycrystalline structure. On the basis of the thickness dependences of the growth processes, this phenomenon was discussed in terms of the diffusion of Si into Fe thin films. 相似文献