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  • Articles: DFG German National Licenses  (3)
  • Solid-state reactions  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 1098-1110 
    ISSN: 0570-0833
    Keywords: Bond theory ; Solid-state reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distinction between valence electrons and essentially inactive core electrons is the basis of many classifying concepts in chemistry. However, it has recently been recognized that this is an oversimplification and should, at least in some areas of chemistry, be modified. Many cases are known where cations with closed d10 configurations are subject to homoatomic interactions that influence structure and properties. A characteristic and surprisingly uniform structural feature (e.g., of a number of compounds containing monovalent coinage metals) is a clusterlike assembly of d10 cations that corresponds in geometry and bond lengths to fragments of the metal structures themselves. Further evidence for a special type of bonding in such compounds is provided by their physical properties; for example, the absorption in the UV/VIS region shows a drastic redshift and the compounds are often conductors or semiconductors. The d electrons in such cases have obviously lost their pure “core” nature. All bonding models so far proposed for such systems involve mixing of higher orbitals.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0570-0833
    Keywords: Alkali metals ; Solid-state reactions ; Ion conductors ; Conducting materials ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transport phenomena in the solid state are of equal importance in basic research and practice. In the past two decades particular interest has been directed towards so-called “fast” or “super” ionic conductors because of their attractive potential applications. We have synthesized highly conductive alkali-metal ionic conductors based on ionic crystals in which, on the one hand, high concentrations of the charge carriers can be realized by doping (point defects in the cation substructure) and, on the other, the activation energy of the interchange of sites is decreased by translationally fixed but rotationally mobile complex anions. Mixed crystals with Na3PO4 or Na3AlF6 structures have proven especially suitable in this connection. With the object of establishing a broader experimental foundation for clarifying the controversially discussed question of whether the higher free transport volume or the rotational motion of the anions is responsible for the high cation mobility in these rotary phases we have systematically varied the type of anions and concentration of defects and monitored the resulting changes in conductivity. Although the macroscopical characteristics investigated are not suitable for explaining mechanisms in detail at the atomic level, the results afford clear support for the assumption of a “paddle wheel mechanism”; but also effects of the enlarged transport volume are not to be disputed. Both these effects enhancing the cationic conductivity are concomitantly operative in amounts varying from system to system; they cannot be totally separated from each other. Seen in this light, the alternative, “volume effect” or “paddle wheel mechanism,” is not as sharply defined as was previously discussed.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 1286-1304 
    ISSN: 0570-0833
    Keywords: computer chemistry ; solid-state structures ; structure prediction ; synthesis planning ; Computer chemistry ; Solid-state reactions ; Solid-state structures ; Solid-phase synthesis ; Structure prediction ; Synthesis design ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented here that allows, in principle, the prediction of the existence and structure of (meta)stable solid compounds. It is based on a set of adjustable modules that are applied to the study of the energy function of the chemical system of interest. The main elements are a set of routines for global optimization and local minimization, as well as algorithms for the investigation of the phase space structure near local minima of the potential energy, and the analysis and characterization of the structure candidates. The current implementation focuses on ionic compounds, for which empirical potentials are used for the evaluation of the energy function in the first stage, and a Hartree-Fock algorithm for refinements. The global optimization is performed with a stochastic simulated annealing algorithm, and the local minimization employs stochastic quenches and gradient methods. The neighborhoods of the local minima are studied with the threshold algorithm. The results of this approach are illustrated with a number of examples: compounds of binary noble gases, and binary and ternary ionic compounds. These include several substances that have not been synthesized yet, but should stand a fair chance of being kinetically stable, for example further alkali metal nitrides besides Li3N, as well as Ca3SiBr2 or SrTi2O5.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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