Showing papers on "Valency published in 1982"

Valence state of cerium in the hexagonal CeM5 compounds with the transition metals

Abstract: 2014 The valence state of cerium in CeCo5, CeNi5, CeCu5 and the pseudo-binary Ce(Ni1-xCux)5 compounds has been studied by means of measurements of lattice parameters, magnetic properties and X-ray absorption. Whereas the lattice parameters of CeCu5 correspond to a Ce3+ valence state, X-ray absorption experiments show that, in CeCo5 and CeNi5, Ce has the same valence state, close to 4 +, as in the insulator CeO2. Stoichiometry deviations in the RCo5 compounds (R = rare earth) can be correlated with the difference in the anomalies of the 03B1 lattice parameter of Ce compounds in the RCo5 and RNi5 series. In Ce(Ni0.1Cu0.9)5, Ce is in the 3+ state and the thermal variation of the susceptibility is characteristic of crystal field effects in the Ce3+ ion. In contrast the susceptibility of CeNi5 is one order of magnitude smaller and almost isotropic; as in YNi5, it arises mainly from the Ni 3d electrons which are close to the onset of ferromagnetism. In the Ce(Ni1-xCux)5 compounds, the Ce valence state decreases linearly with x up to x = 0.3 and more rapidly for higher copper concentrations. The evolution of the Ce valence state is discussed in terms of the band structure of the different compounds, especially the relative position of the Fermi level and the 4f1 state. J. Physique 43 (1982) 173-180 JANVIER 1982,

The cerium metallic radius in AB2 (C15) laves compounds (A ≡ Ce)

Abstract: The anomalous contraction that cerium undergoes when it is the A component in AB 2 Laves phase compounds is used to estimate its metallic radius when it is joined to a given B component. In each case, isostructural compounds of trivalent (rare earths) and tetravalent (zirconium, hafnium and thorium) A elements with the same B element are taken as the reference system. The trivalent metallic radius ( r 3 = 1.846 A ) of cerium proposed by Gschneidner and Smoluchowski was confirmed, but a tetravalent metallic radius ( r 4 = 1.688 A ) of cerium which exceeds their value by 1% was obtained. The presence of A-B contacts is related to the intermediate valency behaviour, and the valency calculated for each compound is compared with other physical properties. A distinction between localized conduction band hybridization and interconfigurational fluctuation is proposed.

Valence state of europium in EuPd3Bx alloys: Lattice constant and susceptiblity studies

Abstract: New boron‐containing alloys of the formula EuPd3Bx have been synthesized by alloying EuPd3 (having the AuCu3‐type structure) with boron. The boron presumably occupies the vacant body‐centered position in the EuPd3 unit cell and results in the expansion of the lattice. The increase in cell volume is observed to be much larger in EuPd3Bx alloys compared to that, for instance, in LaPd3Bx and GdPd3Bx alloys and suggests a possible change in the valency of europium from trivalent towards divalent on boron addition. Susceptibility measurements on EuPd3Bx alloys have verified the valence change of europium ions.

Dynamics of molecules using semigroup techniques: Vibrational line shapes in exciton models of mixed valency

Abstract: The vibrational line shapes expected for a case of ’’excitation mixed valency’’ (defined, in analogy, to ordinary electronic mixed valency, as one exciton moving between two equivalent electronic sites) is studied using a semigroup formalism to include relaxation effects. We include the quadratic electron‐vibration coupling, corresponding to frequency changes. The results demonstrate the line narrowing expected in the rapid exchange limit, but also show that similar behavior may be caused by rapid electronic excitation. The simple model is readily extended to include transfer rates and ordinary (electronic) mixed valency. The relaxation process introduced a new time scale into the problem; when this becomes of the order of other relevant time scales (transfer, vibration, barrier residence) interesting line shape phenomena may be observed.

Substitutional Doping of a-SixNi1-x: H

Abstract: Substitutional doping of a-SixNi1-x: H and the structural properties have been systematically investigated. Valency control of a-SixN1-x: H is found to be possible, although the efficiency of phosphorus doping is rather low with respect to that of boron doping. Vibrational spectra of boron-doped films showed the presence of a considerable amount of the BN bonds, which reduces the amount of the SiN bonds in the network, while phosphorus-doped films contain no PN bonds. Excellent thermal stability of undoped a-SixN1-x: H and the absence of photostructural change are also confirmed.

Changes of valency state during electro-chemical machining

Abstract: When electro-chemical machining of medium and low carbon steels in NaCl electrolytes, a reduction in current efficiency results that is shown here by A.R. Mileham ∗ , R.M. Jones ∗∗ and S.J. Harvey ∗∗ to be associated with a change in the valency from Fe 2+ and Fe 3+ as either the current density is increased or the electrolyte inlet velocity reduced. During the valency transition, surface defects appear. Machining with Fe 2+ rather than Fe 3+ results in a slightly lower value of surface roughness ( R a )