Studies of valence bands and core levels of solids by photoelectron spectroscopy are described at length. Satellite phenomena in the core level spectra have been discussed in some detail and it has been pointed out that the intensity of satellites appearing next to metal and ligand core levels critically depends on the metal-ligand overlap. Use of photoelectron spectroscopy in investigating metal-insulator transitions and spin-state transitions in solids is examined. It is shown that relative intensities of metal Auger lines in transition metal oxides and other systems provide valuable information on the valence bands. Occurrence of interatomic Auger transitions in competition with intraatomic transitions is discussed. Applications of electron energy loss spectroscopy and other techniques of electron spectroscopy in the study of gas-solid interactions are briefly presented.
Infrared spectra of a few transition metal and rare earth formates have been studied. The separation between the νasym and νsym frequencies of the carboxylate ion is not very diagnostic in understanding the nature of metal-anion bonding in the formates. The metal-oxygen stretching frequencies, however, provide some evidence for metal-formate coordination. Electronic spectra show that there is strong coordination between the formate ion and transition metal ions. Thermal decompositions of transition metal and rare earth formates have been studied employing t.g.a. and d.t.a. Rare earth formates just as the acetates first decompose to oxycarbonates and then to the sequioxides; the heavier rare earth formates decompose at lower temperatures. All the evidence seems to indicate greater covalency of the metal-anion bonds in the heavier rare earth formates.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHeats of crystallization of some amorphous oxidesM. Natarajan, G. V. Chandrashekhar, and C. N. R. RaoCite this: J. Chem. Eng. Data 1968, 13, 2, 235Publication Date (Print):April 1, 1968Publication History Published online1 May 2002Published inissue 1 April 1968https://pubs.acs.org/doi/10.1021/je60037a029https://doi.org/10.1021/je60037a029research-articleACS PublicationsRequest reuse permissionsArticle Views73Altmetric-Citations5LEARN 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
Some of the compositions of the half-doped rare-earth manganates, La0.5−x Ln x Ca0.5MnO3 (Ln=Nd, Pr) and Nd0.5Ca0.5−x Sr x MnO3 with relatively small A-cation radii, 〈r A〉, show an unusual behavior wherein they become ferromagnetic (FM) on cooling the charge ordered (CO) state (T CO>T C). With increase in 〈r A〉, however, the T C becomes greater than T CO. Thus, plots of T C and T CO against 〈r A〉 for La0.5−x Ln x Ca0.5MnO3 (Ln=Nd, Pr) and Nd0.5Ca0.5−x Sr x MnO3 show cross-over from the T CO>T C regime to the T C>T CO regime around 〈r A〉 values of 1.195±0.003 and 1.200±0.005Å, respectively. Between T C and T CO, the CO and FM phases are likely to coexist. In Nd0.5Ca0.5Mn1−x M x O3 (M=Cr, Ru), T CO>T C when x≤0.10, suggesting the re-entrant nature of the FM transition.
The formation of complexes between electron donors and acceptors has long been recognized a s an important phenomenon. Many of themolecular complexes are colored and give rise to new absorption bands in the electronic spectra. These molecular complexes have been investigated by employing a variety of physical methods such as optical spectroscopy, magnetic resonance spectroscopy, calorimetry, dielectric measurements, and X-ray diffraction. Studies of donor-acceptor complexes are of value in understanding various types of reaction mechanisms, including molecular phenomena in biological systems. Some of the relatively recent developments in the study of molecular complexes are: the classification of donors and acceptors by Mulliken [l], vibrational spectroscopy, particularly in the very-low-frequency region [2,3], estimation of the per cent charge transfer by dipole moment measurements [4–6], studies of weak interactions (contact pairs) [7], spectra and thermodynamics of complexes in vapor phase [8,9], study of radical ions produced by charge-transfer intermediates [10,11], charge-transfer processes in biological systems [12], and thermal as well as photochemical reactions involving charge-transfer processes [10].
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Pure CoO nanoparticles in the 4.5−18 nm range have been prepared by the decomposition of Co(ΙΙ) cupferronate in Decalin at 270 °C under solvothermal conditions. The particles have been characterized by X-ray diffraction, transmission electron microscopy, and cognate techniques. The particles are stable because of the organic coating that occurs in situ. The organic coating is readily removed by heating the particles to 260 °C without loss of the nanoparticulate nature. Magnetic measurements reveal the presence of ferromagnetic interactions at low temperatures in the small CoO nanoparticles (<16 nm). The small nanoparticles do not exhibit a distinct antiferromagnetic transition around 300 K as the bulk sample but instead show hysteresis below a blocking temperature of ∼10 K.
Mesoporous silicophosphates containing up to 22% phosphorus were prepared using cationic surfactants. A mesoporous silicophosphate of the approximate composition Si19P4O48 had a surface area of 770 m2g−1, after removal of the template. A thermal transformation from a lamellar to a hexagonal structure was observed in this solid. The mesoporous silicophosphate phases were characterized by infrared and NMR spectroscopy.
Unlike the air-water interface, the organic-aqueous (liquid-liquid) interface has not been exploited sufficiently for materials synthesis. In this Account, we demonstrate how ultrathin nanocrystalline films of metals such as gold and silver as well as of inorganic materials such as semiconducting metal chalcogenides (e.g., CdS, CuS, CdSe) and oxides are readily generated at the liquid-liquid interface. What is particularly noteworthy is that single-crystalline films of certain metal chalcogenides are also obtained by this method. The as-prepared gold films at the toluene-water interface comprise fairly monodisperse nanocrystals that are closely packed, the nature and properties of the films being influenced by various reaction parameters such as reaction temperature, time, reactant concentrations, mechanical vibrations, and the viscosity of the medium. The surface plasmon band of gold is markedly red-shifted in the films due to electronic coupling between the particles. The shift of the surface plasmon band of the Au film toward higher wavelengths with an accompanying increase in intensity as a function of reaction time marks the growth of the film. Depending on the reaction temperature, the Au films show interesting electrical transport properties. Films of metals such as gold are disintegrated by the addition of alkanethiols, the effectiveness depending on the alkane chain length, clearly evidenced by shifts of the surface plasmon bands. A time evolution study of the polycrystalline Au and CdS films as well as the single-crystalline CuS films is carried out by employing atomic force microscopy. X-ray reflectivity studies reveal the formation of a monolayer of capped clusters having 13 gold atoms each, arranged in a hexagonal manner at the toluene-water interface. The measurements also reveal an extremely small value of the interfacial tension. Besides describing features of such nanocrystalline films and their mode of formation, their rheological properties have been examined. Interfacial rheological studies show that the nanocrystalline film of Ag nanoparticles, the single-crystalline CuS film, and the multilayered CdS film exhibit a viscoelastic behavior strongly reminiscent of soft-glassy systems. Though both CuS and CdS films exhibit a finite yield stress under steady shear, the CdS films are found to rupture at high shear rates. An important advantage of the study of materials formed at the liquid-liquid interface is that it provides a means to investigate the interface itself. In addition, it enables one to obtain substrate-free single-crystalline films of materials.
Charge ordering occurs in some mixed-valent transition metal oxides. The perovskite manganates of the formula Ln1-xAxMnO3 (Ln = rare earth; A = Ca, Sr) are especially interesting because long-range ordering of the Mn3+ ( ) and Mn4+ ( ) ions in these materials is linked to antiferromagnetic spin ordering, and also to the long-range ordering of the Mn3+ (eg) orbitals and the associated lattice distortions. Charge ordering occurs at a higher temperature than spin ordering in some of the manganates (TCO > TN), whereas in some others TCO = TN. Orbital ordering occurs without charge ordering in the A-type antiferromagnetic manganates, but in the manganates where charge ordering occurs, antiferromagnetism of CE-type is found along with orbital ordering. The subtle relations between charge, spin, and orbital ordering are discussed in the article, with special attention to the effects of cation size, chemical substitution, dimensionality, pressure, and magnetic and electric fields. Unusual features such as phase separation and electron−hole asymmetry are also examined.
No abstract is provided for this article.
ADVERTISEMENT RETURN TO ISSUEPREVArticleStructural aspects of high-temperature cuprate superconductorsC. N. R. Rao and B. RaveauCite this: Acc. Chem. Res. 1989, 22, 3, 106–113Publication Date (Print):March 1, 1989Publication History Published online1 May 2002Published inissue 1 March 1989https://pubs.acs.org/doi/10.1021/ar00159a004https://doi.org/10.1021/ar00159a004research-articleACS PublicationsRequest reuse permissionsArticle Views362Altmetric-Citations87LEARN 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 number of 5-(p-substituted)phenyl-1,2,3,4-thiatriazoles have been synthesized by the diazotization of p-substituted thiobenzhydrazides or by the reaction of sodium thiobenzoyl-thioglycollates with sodium azide. The thermal decomposition of these thiatriazoles yields nitriles, nitrogen, and sulphur. 5-Alkyl-1,2,3,4-thiatriazoles are very unstable and readily decompose to nitriles. Infrared and ultraviolet absorption spectra of 5-(p-substituted)phenyl-1,2,3,4-thiatriazoles have been studied. Infrared spectra of several thiohydrazides have also been studied and there appears to be no thiol–thione tautomerism in these derivatives. The thiatriazole ring is found to be electron withdrawing.
