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Bond Valence (bond + valence)
Selected AbstractsRelationship between the Bond Valence and the Temperature Coefficient of the Resonant Frequency in the Complex Perovskite (Pb1,xCax)[Fe0.5(Nb1,yTay)0.5]O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001Heung Soo Park The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb1,xCax)[Fe0.5(Nb1,yTay)0.5]O3 ceramics (x= 0.5, 0.55; 0.0 ,y, 1.0) was investigated, relative to the bond valence of the A- and B-site ions in the ABO3 perovskite structure (such as the barium-, strontium-, and calcium-based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A- and B-sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B-site. Also, the dependence of TCF on the bond valence of the A-site was similar to its dependence on t. [source] Influence of pressure on the lengths of chemical bondsACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2003I. David Brown An expression to describe the force that a chemical bond exerts on its terminal atoms is proposed, and is used to derive expressions for the bond force constant and bond compressibility. The unknown parameter in this model, the effective charge on the atoms that form the bond, is determined by comparing the derived force constants with those obtained spectroscopically. The resultant bond compressibilities are shown to generally agree well with those determined from high-pressure structure determinations and from the bulk moduli of high-symmetry structures. Bond valences can be corrected for pressure by recognizing that the bond-valence parameter, R0, changes with pressure according to the equation [source] Relationship between the Bond Valence and the Temperature Coefficient of the Resonant Frequency in the Complex Perovskite (Pb1,xCax)[Fe0.5(Nb1,yTay)0.5]O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001Heung Soo Park The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb1,xCax)[Fe0.5(Nb1,yTay)0.5]O3 ceramics (x= 0.5, 0.55; 0.0 ,y, 1.0) was investigated, relative to the bond valence of the A- and B-site ions in the ABO3 perovskite structure (such as the barium-, strontium-, and calcium-based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A- and B-sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B-site. Also, the dependence of TCF on the bond valence of the A-site was similar to its dependence on t. [source] Oxygen Position, Octahedral Distortion, and Bond-Valence Parameter from Bond Lengths in Ti1,xSnxO2 (0 ,x, 1)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Toshiya Hirata Based on the virtual crystal approximation (or Vegard's law), the bond lengths of Ti1,xSnxO2 were deduced from those of TiO2 and SnO2, to allow the oxygen position and octahedral distortion to be determined as a function of x. The oxygen positional parameter (u) increased linearly when the Sn4+ cation (which has a larger ionic radius) was substituted for the Ti4+ cation, whereas the octahedral distortion exhibited a nonlinear decay with increasing x in Ti1,xSnxO2. At the same time, the bond-valence parameter, which relates bond valence to bond length, so that the central atom in the octahedron can retain a constant valence of +4.0, exhibited a correlation with u for Ti1,xSnxO2. The present results indicate that the different phonon/physical properties of TiO2 and SnO2 and/or their dependence on x in Ti1,xSnxO2 can be associated with different octahedral distortions. [source] Atomvolumen, Packungsdichte der Atome und chemische Bindung in nichtmetallischen ElementenACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2007M. Trömel The atomic volume of crystalline elements is largely determined by the packing density of atoms in the respective modification. The determination of packing density is improved by assuming that the atomic distances depend on bond valences according to Pauling's equation. With the additional assumption of equal valence in different modifications, the experimental atomic volume of an element in any given structure is reduced to its volume in close-packed structures, e.g. f.c.c. The ratio of this reduced atomic volume and the experimental atomic volume is a measure of packing density. Reduced atomic volumes of C, Si, Ge, P, As, S and Se, as calculated from different modifications, correspond in most cases to within less than ±1% for each element, even if calculated from extremely different structures like diamond and buckminsterfullerene in the case of carbon, or from numerous modifications of sulfur with annular molecules of different sizes. Exceptions (graphite, white phosphorus, tin and selenium) indicate deviating valences. [source] NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine,Acid ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Hans-Heinrich Limbach Prof. Abstract In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine,acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine,acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. [source] | ||||||||||