J.L. Soubeyroux

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.

Structure and thermal expansion of LiGe2(PO4)3

Abstract LiGe2(PO4)3 belongs to the Nasicon-type family. Room-temperature structure has been determined on a single crystal from 3D X-ray data. Thermal evolution of this structure has been established from neutron powder diffraction data between 300 and 1000 K using the Rietveld method. The thermal expansion is positive along the c-axis, whereas shrinking is observed along the a-axis below 900 K, followed by dilatation. The atomic displacements noted with increasing temperature are consistent with a model proposed for NaZr2(PO4)3.

On an intermediate electronic configuration of cobalt (+III)

Abstract In a D 4h site with a strong elongation the 3 A 2g term of cobalt (+III) can be stabilized with an electronic configuration intermediate between low spin ( 1 A 1g ) and high spin ( 5 E g ): d 2 xz d 2 yz d 1 xy d 1 z 2d 0 x 2 −y 2. The La 2 Li 0.5 Co 0.5 O 4 phase, whose layer structure favours strongly such a distortion of the CoO 6 octahedra, illustrates very well this possibility for cobalt (+III). 1 A 1g → 3 A 2g and 1 A 1g → 5 E g transitions appear as the temperature increases.

Neutron diffraction investigation of the cationic distribution in the structure of the spinel-type solid solutions Li2−2xM1+xCl4 (M = Mg, V): Correlation with the ionic conductivity and NMR data

Abstract The structure of the spinel-type solid solutions Li2−2xMin1+xCl4 M = Mg, V has been studied by neutron diffraction. The cationic distribution in the stoichiometric phases Li2MgC14 and Li2 VCl4 is inverse at room temperature, but some vacancies tend to appear in the tetrahedral 8(a) sites. With increasing temperature a gradual migration of the Li+ ions from the 8(a) positions into the octahedral 16(c) ones has been established for Li2MgCl4. The extra vacancies in the highly deficient spinels LiMgCl3 and LiVCl3 ( x = 1 3 ) have been found to be located in the tetrahedral 8(a) sites only. The correlation between the thermal evolutiomn of the cationic dustribution and the corresponding conductivity and NMR data gives a satisfying interpretation of the jump mechanisms responsible for the high ionic mobility in these materials.

Etude des proprietes structurales et electriques de la solution solide Pb1−xBixOxF2−x

Abstract An investigation of the PbF 2 BiOF system at 600°C has allowed to isolate a Pb 1-x Bi x O x F 2-x solid solution for x ⩽ 0.67 the structure is of fluorite type and for 0.67 1-x Bi x O x F 2-x has electrical performances of the same order than those of the best so far known fluorides. Bragg neutron diffraction investigations have been carried out in order to account for the electrical behavior of the cubic solid solution (0 8 (X = O,F) allows to understand the evolution of the electrical properties.

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.

Proprietes magnetiques de la phase Sr1,50La0,50MnO4

Abstract The crystallographic, electrical and magnetic properties of Sr 1,50 La 0.50 MnO 4 which has a K 2 NiF 4 -type structure show the existence of ferromagnetic clusters due to Mn 3+ Mn 4+ short range ordering antiferromagnetically coupled.

The Nasicon-like copper(II) titanium phosphate Cu0.50Ti2(PO4)3

Cu/sub 0.50/Ti/sub 2/(PO/sub 4/)/sub 3/ is a Nasicon-type phase with a cooperative Jahn-Teller distortion below 550/sup 0/C. Crystal field, electron paramagnetic resonance, and magnetic data seem to be consistent with an octahedral surrounding and a d/sub x/sup 2/-y/sup 2///sup 1/ ground state of Cu/sup 2 +/.

Etude par diffraction de neutrons de la solution solide Pb1−1xThxF2+2x

Abstract Bragg neutron diffraction studies have been carried out on the fluorite type solid solutions Pb 1−x Th x F 2+2x (0 0.875 Th 0.125 F 2.25 , which corresponds to a maximum of vacancies.

On a new structural type of fluorine compounds : Crystal and magnetic structures of a high pressure form of PdF2

A new structural type of MF2 fluorine compounds has been studied using neutron diffraction. The structure of the high pressure form of Pd difluoride has been shown to derive from the fluorite type by a rhombohedral distortion of the cubic environment of the cations. The coordination number of the cations is VI + II : the six nearest neighbor fluorine atoms form a distorted octahedron with M−F1 ⋍ 2.18 A, while two further anions correspond to M−F2 ⋍ 3.17 A. Distances and angles have been compared with those of other Pd compounds. The structure of the high pressure form of PdF2 has been refined via neutron diffraction (a = 5.329 A, space group Pa3 or P213). This phase orders antiferromagnetically below 190 ± 5 K and the magnetic structure has been determined on the basis of both collinear and noncollinear models. The magnetic data have been compared with results obtained for other d8 or d9 difluorides.