Showing papers on "Valency published in 1983"
TL;DR: In this article, the electronic structure of CeO2 and PrO2 was determined by performing SCF band calculations, and it was shown that in both systems there are metal f-and d- electrons in the oxygen 2p bands.
243 citations
TL;DR: In this article, a quantum chemical definition of the valency of an atom in a molecule is proposed, defined as the sum of the squares of the appropriate offdiagonal elements of the first-order density matrix of the system in an orthogonal basis.
Abstract: A quantum chemical definition of the valency of an atom in a molecule is proposed. It is defined as the sum of the squares of the appropriate offdiagonal elements of the first-order density matrix of the system in an orthogonal basis. It is a measure of the degree of electron sharing of the given atom with the other atoms. Its properties such as invariance to rotation of the coordinate system, its limiting values as well as its relation to natural hybrids and bond orbitals are discussed.
191 citations
TL;DR: In the last decade, the Mossbauer technique has made a considerable contribution to the research of the phenomena of mixed valencies, valence instabilities and fluctuating intermediate valencies of transition elements.
Abstract: In the last ten years the Mossbauer technique has made a considerable contribution to the research of the phenomena of mixed valencies, valence instabilities, valence fluctuations and intermediate valencies of transition elements. The sensitivity of the hyperfine interaction parameters and in particular the isomer shift, to the valency of the Mossbauer ion, enabled the research of dynamics of valence fluctuations and the temperature, pressure and composition dependence of the ionic intermediate valence state. Studies of149Sm,152Sm and153Eu in Sm1−xRxS contributed to the understanding of the outstanding insulator-metal phase transition that occurs in these systems. Studies of57Fe and151Eu in mixed valent systems yield the charge fluctuation rates of the “hopping” mechanism, contributing to the conductivity in these systems. Studies of151Eu in EuRh2, EuCu2Si2, EuPd2Si2, EuFe4Al8, and EuPd6B4 as a function of temperature and pressure reveal many aspects of the thermodynamics of intermediate valencies. Studies of systems like Eu1−xLaxRh2, EuA2−xBx, EuA5−xBx reveal strong local environment dependence of the intermediate valency. Mossbauer spectra of169Tm in TmSe,170Yb in YbAl3 and237Np in NpOs2 also display phenomena associated with fluctuating valencies.
58 citations
TL;DR: In this article, a quantum chemical definition of valency is used to calculate the valency of carbon, nitrogen, oxygen, lithium, beryllium and boron in a number of compounds with the SINDO1 method.
Abstract: A quantum chemical definition of valency proposed in Part I is used to calculate the valency of carbon, nitrogen, oxygen, lithium, beryllium and boron in a number of compounds with the SINDO1 method. It is demonstrated that consistency of the basis set is necessary for comparable results. The general features of valency and bonding in these molecules are discussed. The π-electron concept of free valence is generalised to sigma systems and atoms in molecules are classified as subvalent, normal or hypervalent. The relation between valency and natural hybrid occupancy is illustrated. The symmetry properties of natural hybrid orbitals are discussed by means of group theory. A preliminary attempt is made to relate covalency and covalent reactivity. Bond indices and the σ, π character of bonds are obtained by a suitable partitioning and projection of valency into bonding and antibonding contributions.
58 citations
01 Jan 1983
40 citations
TL;DR: In this article, the electronic state of cerium in the pseudo-binary systems Ce (Co1−x�€ 0.76 (∼ 51% Ni) and Zr(Co 1−x€ 1.0) has been studied by means of magnetic susceptibility measurements and by room-temperature X-ray diffraction.
Abstract: The pseudo-binary systems Ce (Co1−x
Ni
x
)2 (and for comparison, Zr(Co1−x
Ni
x
)2), 0⩽x⩽1.0 have been studied by means of magnetic susceptibility measurements and by room-temperature X-ray diffraction. The experimental data indicate that the electronic state of cerium in the Ce(Co1−x
Ni
x
)2 alloys is variable as a function of composition, and the behaviour is interpreted on the basis of a comparison with the similar system Zr(Co1−x
Ni
x
)2 in which zirconium is regarded as a stable tetravalent element. A limit in the stability of the Laves phase in the Zr(Co1−x
Ni
x
)2 system has been found at x−0.76 (∼ 51at% Ni); this behaviour is interpreted in terms of the electron concentration reaching a maximum value for the stability of the cubic Laves phase structure in these alloys. The Laves phases in the Ce(Co1−x
Ni
x
)2 alloy system form a complete solid solution; this behaviour is interpreted in terms of the stability of the structure being maintained across the whole composition range by changes in the effective valency of the cerium atoms as the cobalt atoms are substituted by nickel, i.e. a “valency compensation” effect. From a comparison with the lattice parameter of the Zr(Co1−x
Ni
x
)2 alloys it was possible to determine an approximate value of 3.4 for the effective valency of cerium in the CeNi2 phase.
38 citations
TL;DR: In this article, the authors present neutron scattering data on two intermediate valence dilute Tm alloys: Tm 0.05 La 0.95 Se and Tm0.05 Y 0. 95 Se.
14 citations
TL;DR: This paper is intended to be a starting point for a possible description of all vertex transitive graphs of valency 3 in terms of graphs which can be built up from graphs of smaller valency, bipartite graphs and graphs on which simple groups act as groups of automorphisms.
9 citations
Journal Article•
9 citations
TL;DR: In this paper, a model for the evaluation of activity coefficient ratios in mixed dilute solution is employed with particular respect to ternary cation exchange in zeolites in the presence of up to three different coanions in solution.
Abstract: A previously developed model for the evaluation of activity coefficient ratios in mixed dilute solution is employed with particular respect to ternary cation exchange in zeolites in the presence of up to three different coanions in solution. Potential errors arising from ignoring either completely or partially the non-ideality correction for the solution phase are evaluated and discussed. Exchanges involving counter-ions of the same valency, or involving ions of different valencies, are both considered. It is shown that when all the counter-ions have the same valency, the magnitude of the non-ideality correction is independent of the selectivity of the exchanger. When the valencies of the counter-ions are different it is essential to apply the mixed-salt activity correction for any accurate studies of ternary ion-exchange equilibria.
8 citations
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TL;DR: In this article, the authors showed that TmSe has an anomalous large bulk modulus and a negative c12.3 meV gap, which was first shown by point contact spectroscopy (PCS).
TL;DR: The results of the X-ray diffraction and 195 Pt NMR studies on CePt 2− x Rh x suggest that the valency of Ce changes continuously from 3+ towards 4+ in this pseudobinary alloy as the value of x is increased as discussed by the authors.
TL;DR: In this paper, changes in peak profiles and peak energies of titanium X-rays with both valency and ligand environment changes have been observed, and it is suggested that such shifts, together with changes in Kβ peak profiles, could be used analytically to determine the valence state of titanium and the chemical nature of the atoms that surround it.
Abstract: Changes in peak profiles and in peak energies of titanium Kα, Kβ1, 3+ Kβ′ and Kβ2,5+ Kβ″ X-rays with both valency and ligand environment changes have been observed Both factors affect Kα but a distinct Kβ′ feature identifies Ti(II) whilst ligand atoms can be identified from the Kβ2,5, Kβ″ energy difference When the ligands are known, the small shifts of the sharp and intense Ti Kα1 peak provide the best indicator of valency It is suggested that such shifts, together with changes in Kβ peak profiles, could be used analytically to determine the valence state of titanium and the chemical nature of the atoms that surround it
01 Jan 1983
TL;DR: In this paper, the electron hopping conductivity of binary amorphous oxides was investigated and it was shown that the electron can hop between transiton metal ions in two valency states, e.g. V+4→V+5.
Abstract: The binary oxide glasses exibit interesting electronic properties such as the electron hopping conductivity. In (V2O5)x(P2O5)100−x binary amorphous oxides the electrical conductivity is realized by tne hopping of the electron between transiton metal ions in the two valency state, e.g. V+4→V+5[1].
TL;DR: In this article, the concept of atomic valency is looked at as a specific response of an atomic system to an arbitrary environment, and it is shown how valency might be related both to previously found Hartree-Fock deformed states and to the isotropy groups of the extrema of the electronic energy functional.
Abstract: The concept of atomic valency is looked at as a specific response of an atomic system to an arbitrary environment. It is shown, on the basis of a mathematical result in group actions theory, how valency might be related both to previously found Hartree–Fock deformed states and to the isotropy groups (up to a conjugation) of the extrema of the electronic energy functional.
01 Jan 1983
TL;DR: In this article, it was shown that nuclides whose proton or neutron numbers lie within three units of a magic number have a level density parameter that is very strongly correlated with the Myers-Swiatecki shell correction to the mass formula.
Abstract: It is shown that nuclides whose proton or neutron numbers lie within three units of a magic number have a level density parameter that is very strongly correlated with the Myers-Swiatecki shell correction to the mass formula. Using this correlation, 93 level densities are calculated from only two adjustable constants, in a semi-empirical fashion.
TL;DR: The effect of cation valency on the value of equivalent counterion supply at maximum exchange has been discussed for zeolites NaA, NaX and NaY in this paper, and it has been suggested that the valency dependence of diffusion was much stronger in the zeolite than in the solution.
Abstract: The effect of cation valency on the value of equivalent counterion supply at maximum exchange has been discussed for zeolites NaA, NaX and NaY. It has been suggested that the valency dependence of diffusion was much stronger in the zeolite than in the solution. © 1983 Taylor & Francis Group, LLC.