Valency

About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.

LXXXVI. Fields around impurity atoms in metals

Abstract: Detailed calculations of the potential around impurity atoms with valency Z+l dissolved in a monovalent metal are reported. The first order or linearization approximation usually employed is avoided, and the basic Thomas-Fermi equation must then be solved numerically. The potentials thus obtained differ significantly from those, predicted by the first order approximation. The differences are always in the direction of a more effective shielding of the point charge Ze. The shielding depends appreciably on the valency of the dissolved impurity, whereas the first order result is a screened potential with a screening radius independent of Z. The connection between the present results and Friedel's second order approximation is briefly discussed. The calculations have then been extended to cover the case when we are dealing with a finite concentration of impurities, using the model of Friedel. Again we find that the results given by the first order approximation are appreciably in error. In all the nu...

Single-crystal Raman spectra of YAlO 3 and GdAlO 3 : comparison to several orthorhombic ABO 3 perovskites

Abstract: Room-temperature-polarized single-crystal Raman spectra have been measured for both GdAlO3 and YAlO3. Both aluminates crystallize in the orthorhombic (Pbnm) perovskite structure. Of the 24 possible Raman modes in 4 symmetries, 20 and 17 modes were observed for gadolinium and yttrium aluminates, respectively. Comparisons of the Raman spectra of these two aluminates to those of 28 other orthorhombic ABO3 perovskites revealed remarkably similar spectral patterns, regardless of chemistry or valency of the cations. Closer examination of the effect of mass, valencies, and size of the cations on the Raman spectra versus composition revealed that for the observed modes, the A cation plays the dominant role in determining the Raman shift. In particular, the one to two lowest energy modes in each symmetry are determined by cation mass and valency no matter what the chemistry. For some perovskites with common A cations, higher energy modes were also strikingly similar. In particular, the calcium perovskites had almost all Ag modes at the same energies despite the greatly varying B cations. The second to the lowest mode in Ag and B1g depended only on A cation mass for all perovskites. The volume plays a minor role throughout but is hard to separate from mass effects because the most massive cations are also the largest. However, if the B-cation is common, for example, aluminates or ferrites, the volume has a minor effect on the higher energy modes. These trends were not observed for all perovskites. Notable exceptions were found if a perovskite is near a phase transition or metastable, as found for three manganites. The effect of increased valency of the A cation from 2–4 to 3–3 perovskites expresses itself as relatively larger Raman shifts for the lowest energy modes. Analog studies of MgSiO3 perovskites should be undertaken with only 2–4 perovskites. The increased understanding for the mode distributions of perovskites allows for better estimates of their thermodynamic properties through vibrational modeling.

Study of the electronic structure of molecules. XV. Comments on the molecular orbital valency state and on the molecular orbital energies

Abstract: The valency state (vs) concept is analyzed in the Hartree–Fock approximation. A valency state “standard” is defined for atoms at infinite separation. A molecular orbital valency state (Movs) is defined from a partitioning technique (bond energy analysis) previously introduced for the Hartree–Fock molecular wave functions. The Movs for a given atom in a molecule is much higher in energy than the vs and its energy varies from molecule to molecule depending on the exact field of the surrounding atoms. The examples selected in the discussion are the CH4 CH3F, CH2F2, CHF3 and CF4 molecules. An analysis of the orbital energies is then given in terms of the bond energy. The importance of the rearrangement effects following ionization of inner shell electrons (simulation of ESCA type experiments) is illustrated with computations of the positive ion for methane and its fluoroderivatives. It is concluded that rearrangement following ionization from inner shells is as important as rearrangements following ionization from valency electrons. A direct consequence is that the orbital energies should not be equated to the inner shell ionization potentials. The computation of such ionization potentials agrees to about 99.5% with ESCA data, when the energy of both the neutral and ionic species are computed; the use of the orbital energies limits this agreement to about 95%.

Local Structure in Orthorhombic and Tetragonal Ba 2 YCu 3 O 7-y : The Role of Oxygen Vacancies for High T c Superconductivity

Abstract: Cu valency and local structure in the orthorhombic and tetragonal phases of high Tc superconductor Ba2YCu3O7-y (0.03