G. Villeneuve

Ionic conductivity of oxides with general formula LixLn1/3Nb1−xTixO3 (Ln = La, Nd)

Abstract Ionic conductivity of phases with general formulaLi x Ln 1/3 Nb 1− x Ti x O 3 ( Ln =La, Nd)has been determined for materials with a small value of x , i.e., in composition range with a Ln 1/3 NbO 3 perovskite related structure. The possible influence on the transport properties of the 2D character of the vacancy sublattice has been investigated by a NMR study on Li 0.05 Nb 0.95 Ti 0.05 O 3 .

Interactions magnétiques dans des groupements binucléaires du Ruthénium +V

Abstract The cationic ordering in the Ba M 1 3 Ru 2 3 O 3 (M = Mg, Ca, Cd, Sr ) oxides which crystallize with the 6H structure gives rise to Ru 5+ Ru 5+ pairs in (Ru 2 O 9 ) clusters. The magnetic properties have been analyzed on the basis of the Heisenberg-Dirac-Van Vleck model: The d electrons are localized on each Ru 5+ ion and interact strongly through antiferromagnetic exchange. The susceptibility curves agree with the H.D.V.V. model. The values of the exchange integrals have been determined by fitting the experimental values.

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.

Ionic conductivity of fluorite-type fluorides

Abstract A review is given of our last results in the field of fluoride-ion conductors with fluorite-type (or related) structure. The results obtained are discussed. PbSnF 4 is the best anionic conductor so far known thanks to strong cationic polarizability. Some electrochemical applications are proposed.

Spectroscopic and magnetic properties of two ferromagnetically coupled nickel(II) dimers [{Ni(terpy)(NCX)2}2](terpy = 2,2′ :6′,2″-terpyridine, X = S or Se). Crystal structure of the thiocyanate

Two new binuclear nickel(II) complexes [{Ni(terpy)(NCX)2}2](X = S or Se) have been prepared from 2,2′ :6′,2″-terpyridine (terpy) ligand. The crystal structure of [{Ni(terpy)(NCS)2}2]1 was solved by direct methods and refined by least-squares analysis to a discrepancy factor of 0.050. The crystals are triclinic, space group P, with lattice constants a= 8.822(2), b= 9.569(1), c= 10.906(1)A, and α= 74.35(1), β= 85.19(2), γ= 78.75(2)°. The dimer, whose halves are related by a crystallographic inversion centre, consists of two nickel atoms co-ordinated to two terpy ligands, two terminal NCS ligands and two end-to-end NCS bridging ligands. Each NiII has a distorted-octahedral environment. The Ni ⋯ Ni distance is 5.633(3)A and the bridging angles are 100.0(8) and 159(2)°. The complex [{Ni(terpy)(NCSe)2}2]2 was found to be isomorphous [a= 8.867(3), b= 9.592(4), c= 11.047(3)A, α= 73.64(3), β= 83.44(3) and γ= 76.67(2)°]. Magnetic susceptibility data, measured from 2 to 300 K, were fitted to the Ginsberg equation, giving the parameters J=+4.9 cm–1, D=–4.3 cm–1 and z′ J′=+0.02 cm–1(NCS) and J=+10.1 cm–1, D=–10.0 cm–1 and z′ J′=+0.01 cm–1(NCSe). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.

Etude par diffraction neutronique des solutions solides K1−xBixF1+2xetRb1−xBixF1+2x

Abstract Bragg neutron diffraction studies have been carried out on the fluorite type solid solutions K 1− x Bi x F 1+2 x (0.50 ⩽ × ⩽ 0.70) and Rb 1− x Bi x F 1+2 x (0.50 ⩽ × ⩽ 0.60). The distribution of the fluorine atoms between normal and interstitial sites is given as a function of substitution rate. A substition mechanism is proposed. Electrical and NMR results on one side and structural data on the other side are correlated. A study of the background as a function of temperature has allowed to determine the static origin of its modulation. By inelastic neutron diffusion, it has been shown that the number of carriers is weak, which involves a high mobility.

Contribution a l'etude structurale des phases V1-xCrxO2

Abstract The authors have determined the phase diagram of the system V 1−x Cr x O 2 (0 ⩽ x ⩽ 0.15) by magnetic susceptibility, D. T. A. and X-ray diffraction measurements. At small chromium concentrations the existence of the intermediate phases M 2 and M 3 , between M 1 and the rutile phase, has been confirmed. But it has been found that M 3 has actually a triclinic symmetry without destruction of the V-V pairs already existing in M 1 . At higher concentrations (x > 0.07) there appears a monoclinic M 4 phase in which the V - V pairs are all destroyed.

Magnetostructural correlations in parallel square-planar halo-bridged copper(II) dimers. Part II: Structure and magnetic properties of [Cu2(terpy)2Br2](PF6)2

Abstract The crystal and molecular structure of bis-μ- bromo-bis [(2,2′:6′,2″ - terpyridyl) copper (II) ] bis (hexafluorophosphate) has been determined from three dimensional single-crystal X-ray diffraction data, collected by counter techniques. The blue crystals belong to the monoclinic system, space group P21/a, with four formula units in a unit cell of dimensions a=20.40(2), b=13.35(2), c=6.453(8) A and β=97.74(9)°. The structure was solved using a refinement procedure and starting with the atomic positions of the isostructural complex [Cu(terpy)- Cl]2(PF6)2, to final agreement factors R=0.071 (Rw=0.077). The structure consists of dimeric molecules bridged by two bromine atoms. The coordination geometry about the copper(II) ion is based on a distorted square pyramid with the bridging ligands occupying the apical and equatorial positions. The other three basal coordination positions are occupied by nitrogen atoms from the terpiridyl ligand. The apical CuBr bond distance is 2.83(9) A, and the equatorial CuBr bond distance is 2.36(4) A. The three copper-nitrogen bond lengths are 1.90(4), 2.01(4) and 2.01(8) A. Both, magnetic susceptibility and ESR data evidenced the existence of exchange coupling. The best fit of the susceptibility data to the susceptibility expression for a pair of exchange coupled S=1/2 ions leads to an evaluation of the singlet-triplet energy gap (2J=−7.3 cm-1). A correlation is proposcd relating the magnetic behaviour to the topology of the coordination polyhedron about the copper(II) ion in bis (μ-halo)- bridged parallel planar dimers.

Diagramme de phases du systeme V1−xAlxO2

Abstract The phase diagram of the V1−xAlxO2 system has been determined by D.T.A. and X-ray diffraction; it is similar to that of the V1−xCrxO2 system previously investigated. The stability of the M1, M2 and T phases with the doping rate is discussed.

Crystal structure, spectroscopic and magnetic properties of the complex [Cu(paphy)(NCS)(SCN)](paphy = pyridine-2-carbaldehyde 2′-pyridylhydrazone). An unusual di-µ-thiocyanato-N bridged copper(II) dimer

The crystal and molecular structure of [Cu(paphy)(NCS)(SCN)](paphy = pyridine-2-carbaldehyde 2′-pyridylhydrazone) has been determined from three-dimensional X-ray data. It crystallizes in the monoclinic space group P21/a with four formula units in a cell of dimensions a= 15.778(3), b= 9.937(2), c= 9.795(3)A, and β= 91.31(2)°. Least-squares refinement of 1 163 reflections with I 2.5σ(I) gave a final R= 0.073 (R′= 0.073). The structure consists of isolated centrosymmetric [Cu(paphy)(NCS)(SCN)]2 dimeric units where the two copper(II) ions are linked in an unusual way through the N end of two N-thiocyanate bridging groups. The resulting co-ordination geometry around each copper(II) ion is elongated tetragonal octahedral. The N bridging atoms occupy simultaneously an equatorial position in the co-ordination sphere of one of the copper atoms and an axial one in the other. The remaining axial positions are occupied by sulphur atoms of the S-bonded thiocyanate groups. Magnetic susceptibility measurements down to 2.8 K and e.s.r. spectra provide evidence of the existence of very weak exchange coupling. These results are discussed on the basis of the structural features. A comparison is made with previously published data on related copper(II) thiocyanate complexes.