Chemistry of intercalation compounds: Metal guests in chalcogenide hosts

The sulfidation of crystalline MoO3 and the thermal decomposition of (NH4)2MoO2S2 to MoS2 via an {MoOS2} oxysulfide intermediate have been studied by means of monochromatic X-ray photoelectron spectroscopy (XPS) and infrared emission spectroscopy (IRES) Several basic steps of the sulfidation reaction could be resolved and explained in terms of the structure of crystalline MoO3 The sulfidation reaction starts at low temperatures with an exchange of terminal O2- ligands of the oxide for S2- by reaction with H2S from the sulfiding atmosphere In subsequent Mo−S redox reactions, bridging S22- ligands and Mo5+ centers are formed Lattice relaxation and further sulfur uptake are the main processes before, at temperatures above 200 °C, direct reactions with H2 occur, during which the Mo5+ centers are converted into the 4+ oxidation state The decomposition experiments with (NH4)2MoO2S2 show that terminal O2- ligands serve as the reactive sites The conversion of terminal MoOt to MoS entities and the subsequent

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Basic reaction steps in the sulfidation of crystalline MoO3 to MoS2, as studied by X-ray photoelectron and infrared emission spectroscopy

Groups 5−7 transition metal oxides (V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, Re2O7) were anchored on a SiO2 support via incipient wetness impregnation and calcination. The molecular and electronic structures of the dehydrated supported metal oxides and the SiO2 support were determined by combined in situ Raman, IR, and UV−vis spectroscopy under dehydrated conditions. In situ Raman characterization reveals that the supported metal oxides are only present as surface species below the maximum dispersion limit (where crystalline metal oxide nanoparticles are absent). In situ IR analysis shows that the surface metal oxides anchor to the SiO2 support at Si−OH and adjacent Si−O−Si sites. The corresponding in situ UV−vis diffuse reflectance spectroscopy indicates that the dehydrated surface metal oxide species are present as isolated structures. Isotopic D2O−H2O exchange demonstrates that the dehydrated surface MOx species possess the MO oxo functionality but no MOH bonds. The number of MO oxo bonds was found to be r...

In Situ Spectroscopic Investigation of the Molecular and Electronic Structures of SiO2 Supported Surface Metal Oxides

Solids with ultralow thermal conductivity are of great interest as thermal barrier coatings for insulation or thermoelectrics for energy conversion. However, the theoretical limits of lattice thermal conductivity (κ) are unclear. In typical crystals a phonon picture is valid, whereas lowest κ values occur in highly disordered materials where this picture fails and heat is supposedly carried by random walk among uncorrelated oscillators. Here we identify a simple crystal, Tl 3 VSe 4 , with a calculated phonon κ [0.16 Watts per meter-Kelvin (W/m-K)] one-half that of our measured κ (0.30 W/m-K) at 300 K, approaching disorder κ values, although Raman spectra, specific heat, and temperature dependence of κ reveal typical phonon characteristics. Adding a transport component based on uncorrelated oscillators explains the measured κ and suggests that a two-channel model is necessary for crystals with ultralow κ.

https://science.sciencemag.org/content/sci/360/6396/1455.full.pdf

Two-channel model for ultralow thermal conductivity of crystalline Tl3VSe4.

Thio and seleno compounds of the transition metals with the do configuration

Orbital valency force field: a good approximation to general valence force field for XY4 (Td) and XY3 (D3h) type molecules

Raman-Spektren von (NH4)2MoO2S2 mit 92Mo und 100Mo

Band contour analysis of compounds with pure isotopes: The E fundamentals of HC35Cl3

Force constants for molecules with secular equations of order n > 2 have been determined with the help of various approximation methods based on the General Valence Force Field. The applicability of the approximations have been tested empirically. It cannot be predicted with certainty whether any approximation method yields reliable force constants. Some methods have been found to be inapplicable. The calculation of off-diagonal force constants with any approximation method is impossible. The principle of the quasi-determination of off-diagonal force constant matrix elements from the form of the G matrix on which most approximation methods are based, is critically discussed. It is shown that diagonal force constants calculated with approximation methods are more reliable if the coupling between the vibrations in the same species is low. The application of approximation methods for the determination of force constants without critical consideration is not meaningful.

Die Anwendbarkeit verschiedener Näherungsmethoden zur Berechnung von Kraftkonstanten bei Säkulargleichungen der Ordnung n > 2 / The Applicability of Different Approximation Methods for the Calculation of Force Constants in Secular Equations of Order n > 2

K.H. Schmidt

Papers

Orbital valency force field: a good approximation to general valence force field for XY4 (Td) and XY3 (D3h) type molecules

Raman-Spektren von (NH4)2MoO2S2 mit 92Mo und 100Mo

Band contour analysis of compounds with pure isotopes: The E fundamentals of HC35Cl3

Die Anwendbarkeit verschiedener Näherungsmethoden zur Berechnung von Kraftkonstanten bei Säkulargleichungen der Ordnung n > 2 / The Applicability of Different Approximation Methods for the Calculation of Force Constants in Secular Equations of Order n > 2

Infrarotspektren von KOsO315N und KOs18O3N sowie kraftfeld des nitridoosmat-ions