Showing papers on "Valency published in 1981"

Paramagnetic point and pair defects in oxide perovskites

Abstract: 2014 A review is given of electron paramagnetic resonance (EPR) research of substitutional defects in ABO3 double oxides crystallizing in the perovskite structure. In section 2, the valency and lattice sites are considered. In section 3, the existence of transition metal-oxygen vacancy pairs, Me-Vo, is reviewed, and in 4, their atomic structure is analysed. In section 5, the determination of the local position of Fe3+ at B sites in crystals undergoing ferroelectric phase transitions is presented, and its anomalously low cubic splitting EPR parameter discussed in 6. J. Physique 42 (1981) 551-557 AVRIL 1981,

Mixed Valency Chemistry: A Survey of 10 Years Progress

Abstract: (1981). Mixed Valency Chemistry: A Survey of 10 Years Progress. International Reviews in Physical Chemistry: Vol. 1, No. 2, pp. 149-193.

The phase diagram of the Eu-Pt system and the valency behaviour of europium and ytterbium intermetallics with platinum

Abstract: In the course of a systematic examination of the possible existence of intermetallic compounds of europium and ytterbium which can show anomalous valency behaviour, the binary phase diagram of the Eu-Pt system was studied by means of differential thermal analysis, X-ray analysis and metallographic analysis. Seven intermediate phases were found to exist: Eu 9 Pt; Eu 5 Pt 2 ; Eu 3 Pt 2 ; Eu 5 Pt 4 ; EuPt 2 ; Eu 2 Pt 7 ; EuPt 5 . For most of these phases the crystal structures and lattice constants were determined. The valency behaviour in these phases together with those formed in the Yb-Pt system was studied by means of magnetic measurements and analysis of lattice dimensions, atomic volumes and ionic radii. The conclusion is that europium and ytterbium can form intermetallic phases with platinum, containing divalent or trivalent ions. Moreover, whereas europium in the platinum-rich side of the EuPt 2 solid solution, and perhaps in Eu 2 Pt 7 , appears to give rise to “mixed valency states”, ytterbium in Yb 2 Pt, Yb 5 Pt 3 and Yb 5 Pt 4 shows “fluctuating valency” behaviour.

Valence states of titanium atoms in non-stoichiometric carbides: X-ray emission spectra and cluster calculations

Abstract: The Kbeta 5 and Lalpha X-ray emission bands of titanium carbide and the compound TiC0.65 are considered. Splittings of the bands have been found for the non-stoichiometric compound. Based upon the correspondence between experimental spectra and the results obtained in MO-LCAO calculations on both defect clusters and complete clusters, the authors conclude that the deviation from stoichiometry causes a change of valency for the transition metal. That valency change leads to an increase in the electronic density of states near the Fermi energy mainly associated with metal d character. No evidence for significant electron localisation at vacancy sites has been found either in theoretical or experimental results.

Dimensional analysis of phases with the A15 β-W structure

Abstract: It is found that the method of dimensional analysis of binary metallic phases M x N y , recently developed by the author, can be applied successfully to a tetrahedrally close-packed structure, e.g . the A15 or β-W type MN 3 , Linear equations are developed for the cell edge a in terms of D M and D N , the atomic diameters for coordination number (CN) 12 of the atoms, and of such valency effects as are apparent; these reproduce the observed a values of 63 phases to within an average of a fraction of a per cent. Differences are found between those phases which have transition metal M components and those which do not. In the former it is the M-N contacts in the icosahedron of N atoms surrounding M that control a , whereas in the latter it is the contacts in the CN 14 polyhedron of four M and ten N atoms surrounding the N atoms that together control a . A pseudo-valency effect occurs for the N atoms in phases with transition metal M components. This appears to result in part from valency considerations and in part from geometrical constraints related to the two close N-N contacts. In this paper we compare phases with the A15 structure, rare earth dihydrides with the fluorite structure and rare earth nitrides with the rock salt structure, in each of which two or more sets of atomic contacts act simultaneously to control the cell dimension. A lemma is provided for such cases to indicate how the individual expected cell edge dependences on D M or D N are to be combined to give the overall expected dependence.

Metal Ions in Unusual Valency States.

Abstract: This paper is concerned with the formation of novel valency states, their characterization and chemical behavior.

On graphs of diameter 2

Abstract: Keywords: diameter 2 ; minimum valency ; maximum valency Note: Professor Pach's number: [012] Reference DCG-ARTICLE-1981-004 Record created on 2008-11-14, modified on 2017-05-12

Evidence for the presence of mixed valency in CeNi2; XPS study

Abstract: 3d core-level X-ray photoemission spectrum of CeNi2 exhibits two distinct sets of structures corresponding to trivalent and tetravalent cerium ions. This study provides direct experimental evidence for the presence of mixed valency in CeNi2.

Simple Spectral Density Approach to the Problem of Mixed Valency

Abstract: A simple spectral density approach is proposed for the extended Falicov-Kimball model to describe the phenomenon of mixed valency observed in 4f-compounds The general influences of typical model parameters, as for instance the Coulomb interaction g between localized f- and itinerant s-electrons or the s-f hybridization V, on characteristic properties of intermediate valence compounds are calculated and discussed Depending on the parameters g and V the theory predicts both first-and second-order transitions as found for the Sm chalcogenides Ein einfaches Spektraldichteverfahren fur das erweiterte Falicov-Kimball-Modell wird vorgeschlagen, nm das Phanomen der in den 4f-Verbindungen beobachteten gemischten Valenz zu beschreiben Die allgemeinen Einflusse von typischen Modellparametern wie zum Beispiel die Coulombwechselwirkung g zwischen lokalisierten f- und itineranten s-Elektronen oder die s-f- Hybridisierung V auf charakteristische Eigenschaften von gemischten Valenzverbindungen werden berechnet und diskutiert In Abhangigkeit von den Parametern g und V sagt die Theorie sowohl Ubergange erster als auch zweiter Ordnung voraus, wie sie fur die Sm-Chalkogenide beobachtet werden

Electrolytic separation of ions of different valency by ion-exchange membranes

Abstract: The transport properties through a cation-exchange membrane were investigated for ions of different valency, using an electric field as driving force. In agreement with theoretical considerations a distinct preference of the higher valent ions was found.

Electronic structures and properties of carbonitride and binary carbide solutions based on titanium and zirconium

Abstract: Experimental results are presented on the metal emission band derived from the valency band of crystals of ZrC-ZrN solid solutions, in particular the MIV, V band of Zr, in a series of intermediate zirconium carbonitrides, where the valency-electron concentration increases monotonically from 8 to 9 electrons per cell with unaltered lattice geometry and a slightly varying lattice parameter. The ZrC-TiC system represents another type of solid solution (MeIV-MeIV-X), in which the number of valency electrons remains unchanged throughout the region of continuous solid-state solubility.

Filling of the outer electron bands in Fe-Co-Me alloys

Abstract: A multiband model is used with measured values of the mean magnetic moment of the alloy $$\overline \mu $$ and the normal Hall constant R0 in calculating the filling of the outer energy bands of FeCobase alloys. In alloys in the Fe-Co and Fe-Co-Ni systems, the valency electrons are distributed between the 4s, 4p, and 3d states, with the d↺ subband filled completely. When FeCo is alloyed with manganese, the 4p band is displaced outside the conduction band, and free states appear in the 3d↺ subband. Similar redistributions of valency electrons occur in ordered and disordered states. A study is made of the concentration dependence of σ(c) and R0 (c) for these alloys.