Systematics in the X-ray photoelectron spectra (X. p. e. s.) of Ti, V, Cr, Mn and Nb oxides with the metal ion in different oxidation states as well as of related series of mono-, sesqui- and di-oxides of the first row transition metals have been investigated in detail. Core level binding energies, spin-orbit splittings and exchange splittings are found to exhibit interesting variations with the oxidation state of the metal or the nuclear charge The 3d binding energies of the monoxides show a proportionality to Goodenough’s ( R — R c ). Other aspects of interest in the study are the satellite structure and final state effects in the X. p. e. s. of the oxides, and identification of different valence states in oxides of the general formulae M n O 2 n -1 and M 3 O 4 . The nature of changes in the 3d bands of oxides under-going metal-insulator transitions is also indicated.
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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Molecular Structure of Pivalonitrile by Electron Diffraction1R. L. Livingston and C. N. Ramachandra RaoCite this: J. Am. Chem. Soc. 1959, 81, 14, 3584–3586Publication Date (Print):July 1, 1959Publication History Published online1 May 2002Published inissue 1 July 1959https://pubs.acs.org/doi/10.1021/ja01523a026https://doi.org/10.1021/ja01523a026research-articleACS PublicationsRequest reuse permissionsArticle Views61Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
A fascinating phenomenon, recently found to occur in certain transition‐metal oxides, is phase separation wherein pure, nominally monophasic oxides of transition metals with well‐defined compositions separate into two or more phases over a specific temperature range. Such phase separation is entirely reversible, and is generally the result of a competition between charge‐localization and ‐delocalization, the two situations being associated with contrasting electronic and magnetic properties. Coexistence of more than one phase, therefore, gives rise to electronic inhomogeneity and a diverse variety of magnetic, transport, and other properties, not normally expected of the nominal monophasic composition. An interesting feature of phase separation is that it covers a wide range of length scales anywhere between 1–200 nm. While cuprates and manganates, especially the latter, provide excellent examples of phase separation, it is possible that many other transition‐metal compounds with extended structures will be found to exhibit phase separation.
High-temperature ferromagnetism in graphene and other graphite-derived materials reported by several workers has attracted considerable interest. Magnetism in graphene and graphene nanoribbons is ascribed to defects and edge states, the latter being an essential feature of these materials. Room-temperature ferromagnetism in graphene is affected by the adsorption of molecules, especially hydrogen. Inorganic graphene analogues formed by layered materials such as BN and MoS2 also show such ferromagnetic behaviour. Magnetoresistance observed in graphene and graphene nanoribbons is of significance because of the potential applications.
Schottky defect energies of alkali halides are calculated by the force balance method employing a modified Born model with higher than van der Waals terms and appropriately adjusted repulsive terms. The energies for various potassium and rubidium halides of NaCl structure show good agreement with the experimental values. Schottky defect energies of CsCl are calculated for the CsCl and the NaCl structures. The calculated value (≈︁ 1 eV) for the CsCl structure is in excellent agreement with the recent experimental value. The Schottky energy of CsCl in the NaCl structure is about 2 eV. The ground state interaction energy between a positive and a negative ion vacancy is determined with the inclusion of van der Waals terms. The values obtained for various alkali halides are in fair agreement with the previous ones. The migration barriers for single and pairs of vacancies in KCl and RbCl are calculated by an energy minimization procedure. The barrier heights compare nicely with the experimental value and reflect the expected trend in various parameters. The values also show that the activation energies for the migration of double vacancies and single vacancies are nearly the same; this result contradicts the generally accepted statement that migration of pairs is less energetic, but supports the recent proposal of Lidiard who obtained this result by employing different repulsive energy expressions in the different interionic regions.
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La2NiO4 and Nd2NiO4 show metallic behaviour above 500 K. La2CuO4 is metallic while Sm2CuO4 and Nd2CuO4 are semiconductors in the range 120–1000 K. These transport properties are explained in terms of the structure and the nature of the delectrons.
Electrochemical reduction of carbon dioxide is a viable alternative for reducing fossil fuel consumption and reducing atmospheric CO2 levels. Although, a wide variety of materials have been studied for electrochemical reduction of CO2, the selective and efficient reduction of CO2 is still not accomplished. Complex reaction mechanisms and the competing hydrogen evolution reaction further complicates the efficiency of materials. An extensive understanding of reaction mechanism is hence essential in designing an ideal electrocatalyst material. Therefore, in this review article we discuss the materials explored in the last decade with focus on their catalytic mechanism and methods to enhance their catalytic activity.
In the present study, we are able to synthesize flakes of the 3R‐polytypes of MoS 2 and WS 2 from sodium molybdate and sodium tungstate in the presence of H 2 S gas by solid‐state reaction. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and X‐ray diffraction are utilized to characterize the morphology, structure, and chemical composition of the 3R‐MoS 2 and 3R‐WS 2 flakes. The electrocatalytic and photocatalytic activities of 3R‐MoS 2 and 3R‐WS 2 flakes have been measured in hydrogen evolution reactions.
The donor-acceptor interactions of alkylthioureas and thiocarbanilides with halogens have been investigated in detail employing electronic and infra-red spectroscopy. Various correlations of the spectroscopic and thermodynamic data have been presented. Alkylthioureas are by far the strongest donors known, and give high equilibrium constants (10,000-40,000 1. mole–1) and enthalpies of formation (9-18 kcal mole–1). The perturbation of the various vibrational frequencies due to charge transfer have also been studied. Hydrogen bonding of thioureas with hydroxylic compounds have been reported.
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The nature of the chemisorbed states of nitrogen on various transition metal surfaces is discussed comprehensively on the basis of the results of electron spectroscopic investigations augmented by those from other techniques such as LEED and thermal desorption. A brief discussion of the photoemission spectra of free N2, a comparison of adsorbed N2 and CO as well as of physisorption of N2 on metal surfaces is also presented. We discuss the chemisorption of N2 on the surfaces of certain metals (e.g. Ni, Fe, Ru and W) in some detail, paying considerable attention to the effect of electropositive and electronegative surface modifiers. Features of the various chemisorbed states (one or more weakly chemisorbed γ states, strongly chemisorbed α states with bond orders between 1 and 2, and dissociative chemisorbed β states) on different surfaces are described and relations between them indicated. While the γ state could be a precursor of the α state, the α state could be the precursor of the β state and this kind of information is of direct relevance to ammonia synthesis. The nature of adsorption of N2 on the surfaces of some metals (e.g. Cr, Co) deserves further study and such investigations might as well suggest alternative catalysts for ammonia synthesis.
Crystal structures and dielectric properties of three recurrent intergrowth structures Bi9Ti6CrO27, Bi9Ti6FeO27, and BaBi8Ti7O27 formed by the Aurivillius family of bismuth oxides of the formula Bi2A n−1B n O3n+3 are reported. The intergrowths exhibit ferroelectricity and accordingly belong to the noncentrosymmetric space group Cmm2. The ferroelectric curie temperatures of the intergrowths are in the 630–1070 K range.
