Topic
Valency
About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.
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TL;DR: The phases with a V valency >4 exhibit low C(44) values, large anisotropy and possess weak ionic bonding between the layers and the formation of easily plastically deformable structures is enabled by the screened Coulomb potential.
Abstract: VO, V2O3, VO2, V6O13, V4O9, V3O7 and V2O5 have been investigated in terms of structure, bulk modulus B and elastic constant C44 using ab initio calculations. The C44 values for V6O13, V4O9, V3O7 and V2O5 are significantly lower than those for V2O3 and VO2. As the V valency is increased from 3 to 5, C44 decreases by 83%, whereas the bulk modulus decreases by 61%, leading to an increase in the B/C44 ratio from 1.4 to 3.4. This is consistent with calculated decohesion energies for cleavage in VO2 and V2O5. When cleaving V2O5, decohesion energies are considerably lower than those of VO2. This behaviour may be understood based on V valency induced changes in the crystal and electronic structure as well as in the chemical bonding. As the V valency is increased, the bond strength decreases. The phases with a V valency >4 exhibit low C44 values, large anisotropy and possess weak ionic bonding between the layers. The formation of easily plastically deformable structures is enabled by the screened Coulomb potential. The largest distance and therefore weakest bond strength is observed for V2O5 in the (002) plane.
51 citations
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51 citations
01 Jan 2006
TL;DR: The paper presents new lexicon of verb valencies for the Czech language named VerbaLex, which comprehends all the information found in these resources plus additional relevant information such as verb aspect, verb synonymity, types of use and semantic verb classes based on the VerbNet project.
Abstract: The paper presents new lexicon of verb valencies for the Czech
language named VerbaLex. VerbaLex is based on three valuable
language resources for Czech, three independent electronic
dictionaries of verb valency frames. The first resource, Czech
WordNet valency frames dictionary, was created during the
Balkanet project and contains semantic roles and links to the
Czech WordNet semantic network. The other resource, VALLEX 1.0,
is a lexicon based on the formalism of the Functional
Generative Description (FGD) and was developed during the
Prague Dependency Treebank (PDT) project. The third source of
information for VerbaLex is the syntactic lexicon of verb
valencies denoted as BRIEF, which originated at FI MU Brno in
1996. The resulting lexicon, VerbaLex, comprehends all the
information found in these resources plus additional relevant
information such as verb aspect, verb synonymity, types of use
and semantic verb classes based on the VerbNet project.
51 citations
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TL;DR: In this article, the structure and bonding in alpha and beta octamolybdate anions have been investigated using density functional methods, and good computational-experimental agreement for the geometrical parameters has been obtained.
Abstract: The structure and bonding in alpha and beta octamolybdate anions have been investigated using density functional methods. In general, good computational-experimental agreement for the geometrical parameters has been obtained. The electronic structure of the anions has been probed with molecular orbital and Mulliken-Mayer methods. All Mo-O interactions have been found to be predominantly d(Mo)-p(O) in character. Several multicentered molecular orbitals can be described as sigma or pi closed-loop structures, but the proposed connection with the stability of the polyanions is not completely supported by the calculations. Mayer indexes correspond to fractional multiple character for terminal bonds and approximately single or low-order character for bridging bonds, in accordance with structural and bond valence results. The valency analysis has yielded similar overall bonding capacity for the various oxygen atoms. A distribution of the negative charge over all types of oxygen sites and metal charges considerably smaller than the formal oxidation states have been obtained from the Mulliken analysis.
51 citations
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14 Mar 2000TL;DR: Orthosilicates containing the SiO 4 4- tetranion as the building block are used as redox materials by incorporation of at least one transition elements with at least two valency levels as mentioned in this paper.
Abstract: Orthosilicates containing the SiO 4 4- tetranion as the building block are used as
redox materials by incorporation of at least one transition elements with at least two
valency levels. Lithium ingresses or egresses from the structure to compensate for the
valency change of the redox couples during electrode operation and keep overall
electroneutrality.
50 citations