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1.
Electrochemical reductive dissolution of Li–Mn–O and Li–Fe–Mn–O spinels and Li + extraction/insertion in these oxides were performed using voltammetry of microparticles. Both electrochemical reactions are
sensitive to the Fe/(Fe+Mn) ratio, specific surface area, Li content in tetrahedral positions, and Mn valence, and can be
used for electrochemical analysis of the homogeneity of the elemental and phase composition of synthetic samples. The peak
potential ( E
P) of the reductive dissolution of the Li–Mn–O spinel is directly proportional to the logarithm of the specific surface area. E
P of Li–Fe–Mn–O spinels is mainly controlled by the Fe/(Fe+Mn) ratio. Li + insertion/extraction can be performed with Mn-rich Li–Fe–Mn–O spinels in aqueous solution under an ambient atmosphere and
it is sensitive to the regularity of the spinel structure, in particularly to the amount of Li in tetrahedral positions and
the Mn valence.
Electronic Publication 相似文献
2.
Fundamentally different behavior of Ba–Bi–O (Ba : Bi = 11 : 4, 1 : 1, 2: 3, and 1 : 5 mol/mol) and K nBa mBi m+nO y ( m = n = 1, 2,...; exhibiting superconducting properties with Tc = 28–32 K) oxides and BaO 2 in hydrolysis reactions has been revealed by means of potentiometry and chemical analysis. Products of the oxides treatment with water do not contain H 2O 2, evidencing the absence of peroxide ions in their structure. The perovskite-type barium-bismuth(III) oxides are completely hydrolyzed into Ba(OH) 2 and Bi 2O 3 at room temperature. 相似文献
3.
The reaction of [{(η 5-Me 5C 5)Co} 2(μ-η 6:η 6-toluene)] with water under different conditions leads to formation of the clusters [{(η 5-Me 5C 5)Co} 3(μ 3-O) 2] ( 1), [{(η 5-Me 5C 5)Co} 4(μ 3-OH) 4] ( 2) and [{(η 5-Me 5C 5)Co} 3(μ 3-OH) 4] 2Co ( 3), whereas its reaction with hydrogen sulfide leads to [{(η 5-Me 5C 5)Co} 3(μ 3-S) 4]Co(μ 3-S) 2[(η 5-Me 5C 5)Co] 2 · Et 2O ( 4). 1, 2 and 4 were characterized by single crystal X-ray diffraction. 1 is composed of a central Co 3O 2 unit, with two O 2- units in an apical postion. The three cobalt atoms form a regular triangle with Co–Co distances of 2.438(2) Å, and the two oxygen atoms are located in apical positions of the triangular arrangement. The pentamethylcyclopentadienyl (Cp*) ligands are terminally bonded to the Co atoms in a η 5-fashion. The Co and O atoms of 2 form a cubane-type Co 4O 4 cluster, with η 5-bonded Cp* ligands. The central unit of 3 consists of a Co 7O 8 double cubane framework. Two Co 4O 4 cluster sharing a common corner (Co atom). Each of the other six Co atoms of the double cubane bound terminally a Cp* ligand. 4 is composed of a [{(η 5-Me 5C 5)Co } 2(μ 3-S) 4](μ 3-S) 2[(η 5-Me 5C 5)Co] 2 and an ether molecule. 4 contains a central Co 4S 4 cubane-like unit. One of the four Co atoms is bonded via two μ 3-S atoms to two additional (η 5-Cp*Co) units. The other three Co atoms are η 5-coordinated to a Cp* ligand. 相似文献
4.
The Mg–Ce–O powder are shown to contain periclase-type MgO and/or fluoride-type cerium oxide (CeO 2) depending upon the composition (x) defined by Ce/(Ce + Mg) atomic ratio. Lattice contraction of pariclase phase of MgO (average crystallite size ~8.8 nm) at Ce content of ‘x’ = 0.20 in comparison to pure MgO (crystallite size ~9.5 nm) has been realized due to oxygen vacancy formation. The optical band gap values of CeO 2 varies (3.0–3.2 eV) due to oxygen vacancy formation in CeO 2 phase, crystallite size and/or Ce 3+/Ce 4+ ratio. Further, the addition of Ce has shown to reduce the physisorption and chemisorption of water significantly as reflected by (1) suppression of related absorption peaks and (2) absence of magnesium hydroxide, Mg(OH) 2, bands in Fourier transform infrared spectra. 相似文献
5.
The work deals with the establishment of the dependence of the vibrational frequencies of strong O–H?O and N–H?O hydrogen bonds for the diagnosing the bonds themselves. To this end, the Raman spectra of a large number of different normal and deutero-substituted crystals characterized by the presence of strong O–H?O and N–H?O bonds are measured and the quantum chemical calculation is performed for one of these compounds. The dependence of the O–H stretching frequency on the O?O distance is constructed differing from that previously known for short O?O contacts. The mechanisms of significant broadening of the O–H vibration band in strong O–H?O hydrogen bonds are considered. Different dependences of the N–H vibrational frequencies in N–H?O bonds are reported and the causes of this diversity are discussed. 相似文献
6.
The Na 2O–CaO–SiO 2 ternary glass–ceramic with the composition of 49 mass% Na 2O, 20 mass% CaO, and 31 mass% SiO 2 was prepared by the conventional method. The ternary glass–ceramic was characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. The Na 2CaSiO 4 phase, having the cubic crystal system, with the crystallite size of 25.14 nm and lattice parameter of 0.7506 nm was determined from the XRD pattern. The activation energy of the glass–ceramic calculated from the DTA curves was found to be 162.02 kJ mol ?1. The Avrami exponent was found to be ~2 indicating a one-dimensional growth process. The mass loss percent from ambient temperature to 1,173 K is less than 1 %. The density was calculated to be 2,723 kg m ?3. The fine-grained microstructure with the particle sizes less than 1 μm was confirmed by the scanning electron microscope micrograph. 相似文献
7.
The phase diagram of the La–Ca–Co–O system at 885 °C in air has been determined. The system consists of two materials that have interesting thermoelectric properties, namely, the misfit layered thermoelectric oxide solid solution, (Ca,La) 3Co 4O 9, and Ca 3Co 2O 6 which consists of 1D chains of alternating CoO 6 trigonal prism and CoO 6 octahedra. The reported La 2CaO 4 and the Ca-doped (La,Ca) 2CoO 4−z phases were not found at 885 °C. As a result of the absence of these phases, the phase diagram is significantly different from that reported at 1100 °C. Small solid solution regions of (La 1−xCa x) 2O 3−z (0 ≤ x ≤ 0.08), (Ca 1−xLa x) 3Co 4O 9 (0 ≤ x ≤ 0.07), and (La 1−xCa x)CoO 3−z (0 ≤ x ≤ 0.2) were established. 相似文献
8.
Thermal stability of PbO was studied. Reactivity of oxides in the systems PbO–M 2O 3 ( M = In, Fe) was investigated up to 650 °C. Using the DTA and XRD methods, parts of investigated ternary oxide systems, labelled by compounds: V 2O 5, Pb 8V 2O 13 and M 2O 3 ( M = In, Fe), have been divided into partial ternary systems. IR spectra of compounds Pb 2MV 3O 11 ( M = In, Fe) have been compared. 相似文献
9.
Dimethyldimethoxysilane, methylphenyldimethoxysilane, and diphenyldimethoxysilane have been synthesized by a one-step, simple
method and used as catalysts in the Henry reaction with Cu(OAc) 2·H 2O and Zn(OAc) 2·2H 2O, affording 60–96% conversion under the optimum catalytic conditions. 相似文献
10.
Within the ternary system Ga–O–N we performed experimental and theoretical investigations on the thermodynamics, structure and kinetics of new stable and metastable compounds.We studied the ammonolysis of β-Ga 2O 3 at elevated temperatures by means of ex situ X-ray diffraction, ex situ neutron diffraction, and in situ X-ray absorption spectroscopy (XAS). From total diffraction pattern refinement with the Rietveld method we analyzed the anionic occupancy factors and the lattice parameters of β-Ga 2O 3 during the reaction. Within the detection limits of these methods, we can rule out the existence of a crystalline oxynitride phase that is not derived from wurtzite-type GaN. The nitrogen solubility in β-Ga 2O 3 was found to be below the detection limit of about 2–3 at.% in the anionic sublattice. The kinetics of the ammonolysis of β-Ga 2O 3 to α-GaN and of the oxidation of α-GaN to β-Ga 2O 3 was studied by means of in situ X-ray absorption spectroscopy. In both cases the reaction kinetics could be described well by fitting linear combinations of β-Ga 2O 3 and α-GaN spectra only, excluding that other crystalline or amorphous phases appear during these reactions. The kinetics of the ammonolysis can be described well by an extended Johnson–Mehl–Avrami–Kolmogorow model with nucleation and growth of GaN nuclei, while the oxidation kinetics can be modeled by a shrinking core model where Ga 2O 3 grows as a layer. Investigations by means of TEM and SEM support the assumptions in both models.To investigate the structure and energetics of spinel-type gallium oxynitrides (γ-galons) we performed first-principles calculations using density-functional theory. In addition to the ideal cubic γ-Ga 3O 3N we studied gallium deficient γ-galons within the Constant-Anion-Model.In highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO 1.2 we found at a temperature around 670 K an insulator–metal transition, with a conductivity jump of seven orders of magnitude. We demonstrate through experimental studies and density-functional theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric β-Ga 2O 3 within the metastable oxide matrix. By doping with nitrogen the critical temperature and the conductivity in the highly conducting state can be tuned. 相似文献
11.
Glasses in the system Li 2O–SnO–B 2O 3 system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B 2O 3 glasses exhibited relatively low glass-transition temperatures ( Tg) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of Tg indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B 2O 3 binary system. 相似文献
12.
Russian Journal of Physical Chemistry A - Isothermal phase diagrams of ternary systems fullerenol-d–LaCl3–H2O and fullerenol-d–GdCl3–H2O at 25°C are studied via... 相似文献
14.
Glasses with compositions 60Bi 2O 3–(40?x)B 2O 3–xGa 2O 3 ( x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga 2O 3. The glass transition temperature ( Tg), the onset crystallization temperature ( Tx), Δ T ( Tx? Tg) decrease with the content of Ga 2O 3. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga 2O 3. On the other hand, the addition of Ga 2O 3 causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi 5+ and Bi 3+ exist in 5 mol% Ga 2O 3 content, while Bi 5+ amounts decrease with the increase of Ga 2O 3 contents. The glass is mainly composed of [BiO 6], [BO 3], [BO 4] and [GaO 4] polyhedra. Glasses are supposed to have layer structure. [BO 3] triangle and [BO 4] tetrahedra may be located between the [GaO 4] tetrahedral and [BiO 6] octahedra to prevent crystallization and to compensate electric charge. 相似文献
15.
Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study
A systematic computational study of four-membered cyclic ketene – O,O– , – O,S– , – O,N– , – S,N– and – N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized
triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and
the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles,
and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies,
and calculated charges. 相似文献
16.
A simple and practical method has been developed based on intermolecular [Pd]-catalyzed C–C and an intramolecular [Cu]-catalyzed C–O bond formations for the synthesis of flavans and benzoxepines. Interestingly, the method is amenable for the synthesis of a wide variety of flavans and benzoxepines with dense functionalities on aromatic moieties. Significantly, flavans and benzoxepines are present as core/part-structures in many biologically active natural products. 相似文献
17.
Small molecule studies indicate that C–H...X interactions (X: O,N) constitute weak H-bonds. We have performed a comprehensive
analysis of their occurrence and geometry in RNA structures. Here, we report on statistical properties of the total set of
interactions identified and discuss selected motifs. The distance/angle distribution of all interactions exhibits an excluded
region where the allowed C–H...X angle range increases with an increasing H...X distance. The preferred short C–H...X interactions
in RNA are backbone-backbone contacts between neighbour nucleotides. Distance/angle distributions generated for various interaction
types can be used for error recognition and modelling. The axial C2′(H)...O4′ and C5′(H)...O2′ interactions connect two backbone
segments and form a seven-membered ring that is specific for RNA. An AA base pair with one standard H-bond and one C–H...N
interaction has been identified in various structures. Despite the occurrence of short C–H...X contacts their free energy
contribution to RNA stability remains to be assessed.
Received: 17 May 1998 / Accepted: 4 August 1998 / Published online: 2 November 1998 相似文献
18.
Spin traps, which are diamagnetic centers (SiO) 2Si, are used to register low-molecular radicals OH, NH 2, and H formed by the reactions of H 2O and NH 3 molecules with the radicals (Si–O) 3Si and (Si–O) 3Si–O stabilized on the silica surface. The experimental data and the results of quantum-chemical calculations for model systems are used to determine the mechanism and thermochemical characteristics of these reactions. A new paramagnetic center (Si–O) 2Si NH 2 was identified on the silica surface, and its radiospectroscopic characteristics are determined. 相似文献
19.
Comprehensive phase diagrams of methanol/CHF 3 and methanol/H 2O/CHF 3 mixtures over the temperature range of 25–100°C and pressure range of atmospheric to 340 atm are reported. Fluoroform is expected to be useful as an alternative to CO 2 for enhancing the fluidity of liquid mixtures due to its high polarity and low viscosity. Therefore, these mixtures will be studied as mobile phases for enhanced-fluidity liquid chromatography and extraction. The phase behavior of methanol/CHF 3 and methanol/H 2O/CHF 3 was compared to that of methanol/CO 2 and methanol/H 2O/CHF 3. Fluoroform is markedly more miscible with methanol or methanol/H 2O than is CO 2. Data for methanol/CHF 3 binary mixtures were also modeled by the Peng–Robinson equation of state. The correlation results showed that the PR equation of state with two temperature-independent binary parameters was capable of representing the experimental data over the entire temperature range with an average relative deviation within 6%. 相似文献
20.
The effect of the SrO addition on the microstructure and structure of the glazes from the SiO2–Al2O3–CaO–MgO–K2O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range. 相似文献
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