Josik Portier

Amelioration des conditions de synthese de l'hydrure de magnesium a l'aide d'adjuvants

Addition of metals or alloys whose hydrides have a high dissociation tension allows a considerable increase of the hydrogenation rate of magnesium. The influence of the nature of the adjuvant and its specific concentration, of temperature and hydrogen pressure on the reaction rate, have been carefully studied. The pressure-composition isotherms have been determined especially when the adjuvant is LaNi5.

Etude par diffraction de neutrons de la solution solide Pb1−xBixF2+x: Correlations entre structure et conductivité ionique

Bragg neutron diffraction studies have been carried out on the fluorite-type solid solutions Pb 1− x Bi x F 2+ x (0≤ x ≤0.50). The distribution of fluorine atoms between normal and interstitial sites as a function of the substitution rate is determined. Electrical and structural data are correlated. These results are compared with those obtained from the Ca 1− x Y x F 2+ x solution.

Etude des proprietes structurales et electrioues d'un nouveau conducteur anionique: PbSnF4

Three allotropic varieties of PbSnF4 - α, β and γ - have been detected by DTA and X-ray diffraction. The α ai β and β ai γ transitions are reversible and occur at 80 and 355°C respectively. The high temperature form γ - PbSnF4 is cubic and of fluorite type. The structures of the tetragonal β - PbSnF4 and the orthorhombic α - PbSnF4 forms are derived from the same structural type. PbSnF4 has a high anionic conductivity (σ200°C ⋍ 10−1 Ω−1cm−1). The temperature dependence of the conductivity indicates the existence of a break in the activation energy at 90°C.

Sur de nouveaux conducteurs anioniques de hautes performances

The study of ionic conduction in fluorides with fluorite type structure leads to new anionic superconductors of formulation Pb1−xBixF2+x (0 ⩽ x ⩽ 0.50). The strong polarizability of the Pb2+ and Bi3+ cations gives a highly conducting material. In particular Pb0.75Bi0.25F2.25 has a conductivity close to that of β-alumina.

Raman spectroscopic studies of fluorophosphate glasses

Some fluorophosphate glasses obtained by fluorination of NaPO3, xNaPO3−yAlF3 or tNaPO3−wAlF3−vCaF2 have been studied by Raman spectroscopy in VV and VH polarisations. The observed bands have been assigned by comparison with those vitreous NaPO3 and Na4P2O7, as well as crystallised K2PO3F and KPO2F2, and molten cryolite. Structural models are proposed for the various compositions. They are built up with arrangements of following species: (PO3)2n−n chains; (P2O7)4− dimers, (AlF6)3− octahedra, P(O, F)4, (AlF4)− and (AlOF3)2− tetrahedral groups. For glasses rich in phosphate −OPO2F− and −OPOF2 terminal groups are displayed; the latter being favoured for a higher fluorine concentration.

The role of the inductive effect in solid state chemistry: how the chemist can use it to modify both the structural and the physical properties of the materials

Abstract The concept of the inductive effect, which is well known in organic chemistry, has been extended to solid-state chemistry. In solid ternary compounds, the cohesion energy of which primarily results from the electrostatic interaction between one type of anion X q − and two types of cations M m+ and T z+ , the inductive effect of T on the M-X bond has been qualitatively assessed by the difference of electronegativity between M and T atoms, showing the limits of this concept. Several correlations between the inductive effect of the countercation T and physicochemical properties depending on the covalent character of the M-X bond have been reviewed: structural modification of oxides, stabilization of unusually high oxidation states of 3d transition elements in oxides and fluorides, vitrification conditions of materials, electrical conductivity of some perovskite oxides, cationic conductivity, magnetic properties, optical properties of divalent europium, Fe 3− /Fe 2− redox potential position in inorganic isostructural compounds and Mossbauer isomer shifts in FeO x and FeF n polyhedra.

Characteristic properties of new solid electrolytes

Abstract Influence of some physical and chemical factors on the transport properties of solid electrolytes has been examined and has allowed to determine several criteria characteristic of high mobility. Materials with high electrical performances have been isolated in the scope of these considerations.

EPR of transition metal ions (Mn2+, Cu2+, Cr3+, Fe3+) in fluoroaluminate glasses

Abstract EPR experiments have been performed on glasses related to the CaF2BaF2AlF3 system. Fluctuations of the EPR parameters are observed in the case of divalent ions which occupy distorted sites. The trivalent ions occupy sites of “fully rhombic” symmetry. A comparison with the EPR parameters obtained for crystallized α-CaAlF5 leads to the conclusion that the glass is built up by random type chains containing aluminium separated in various ways by the divalent cations, the coordination numbers of which may differ.

Nature de la fluorescence de l'europium divalent dans les fluorures

Abstract The levels of the 6 P 7 2 (4f 7 ) and 4f 6 5d 1 states of europium (+II) have been determined from fluorescence spectra in a series of fluorides M x B y F z (M = alkaline-earth element, B = Li, Be, Mg, Y, Si). As in BaY 2 F 8 , SrSiF 6 and BaSiF 6 , the 6 P 7 2 level lies even at room temperature far below the 4f 6 5d 1 band, only the f → f emission is observed. The influence of the choice of the alkaline-earth and the B cations and of the coordination of europium on the relative positions of the energy levels is discussed.

Structural approach of the (xPbCl2-(1−x)Sb2O3) glass system

A structural approach of xPbCl2, (1 − x)Sb2O3 glasses, quenched from the melt, is proposed. The crystallization process of the glasses is analyzed and a Raman scattering investigation is reported. The two investigations give valuable information on the structural arrangement of the glass network. Observations within the xPbCl2, (1 − x)Sb2O3 system show variations of local structure and a comparison is made with previously reported data for some Sb or As based glasses.