A. Bouamrane

Structural characterization of NaMgH2F and NaMgH3

The direct reaction of hydrogen on a mixture of Na + Mg or NaF + Mg allowed for synthesis of NaMgH3 and NaMgH2F, respectively. Both phases were indexed with an orthorhombic unit cell with dimensions a = 546.34, b = 770.30, c = 541.08 pm for NaMgH3 and a = 547.59, b = 769.68, c = 540.31 pm for NaMgH2F. The crystal structures were refined by X-ray Rietveld refinement. They derive from the perovskite structure type by a Pmm → Pnma distortion. In the hydridofluoride, H− and F− anions are equally distributed in the two anionic sites in a disordered way.

Structural characterization of new hydridofluorides KCaH3−xFx with x=1; 1.5; 2; 2.5

Abstract The direct reaction of hydrogen on a mixture KF, CaH 2 and CaF 2 in stoichiometric proportions allowed to synthesize a series of discrete phases KCaH 3− x F x with x =1, 1.5, 2 and 2.5. All phases were indexed with an orthorhombic unit cell [e.g.: a =623.47(5), b =881.05(8), c =620.83(6) pm for KCaHF 2 ]. Their crystal structures are isotypic with KCaF 3 and have been refined by a X-ray Rietveld study. They derive from perovskite type by a Pm -3 m → Pnma distortion. Contrary to the homologous NaMgH 2 F in which H − and F − anions are equally distributed in a disordered way in the two anionic sites 4c and 8d, in the KCaH 3− x F x series, the hydride ions preferentially occupy the 8d site and begin to occupy the 4c site only for the two compositions richer in hydrogen.

Variations en fonction de la temperature de la capacite calorifique et des proprietes dielectriques du dihydrurofluorure de magnesium-potassium a structure perovskite KMgH2F

Abstract Thermal and electrical properties of a new perovskite-like hydridofluoride KMgH 2 F have been investigated up to 300°C. Two anomalies are observed on the variation of the heat capacity in the vicinity of 55 and 180°C respectively revealing the typical behavior of many ferroelectric substances. Electrical measurements confirm this behavior. The first anomaly is probably related to a coupling of ferroelastic and ferroelectric properties. The second one could be unambiguously explained in terms of a ferro-paraelectric transition.

Caracterisation par analyse calorimetrique differentielle des complexes entre LiAlH4 et les ethers-couronnes 12-C-4, 15-C-5, dicyclohexano-18-C-6

The thermal behaviour of complexes [Li+-EC](AlH4)− withEC=12-C-4, 15-C-5, DC 18-C-6 (cis-anti-cis andcis-syn-cis isomers) was investigated by Differential Scanning Calorimetry (DSC). These complexes were prepared as solids from benzene solutions. Pure EC and several solvated species [Li+-EC](AlH4)−·nC6H6 (EC=15-C-5, DC 18-C-6syn) were also studied. DSC has revealed various phenomena. Solid-solid transitions were observed before melting for [Li+-EC](AlH4)− withEC=12-C-4 and 15-C-5. They are probably explained by small molecular modifications strongly dependent on the thermal history of the sample. A glass-transition was found for the pure crown-ether DC 18-C-6anti, the complex [Li+-EC](A1H4)− withEC=DC-18-C-6anti and the two solvates mentioned above.

Conductivité anionique des hydrures et fluorures d'ytterbium YbH1,8, YbH2,5, YbF2,33, YbF3 et de la solution solide YbH1,8-nYbF2,33 (1,75≤n≤1,95)

Measurements of conductivity have been performed up to 250 °C for several ytterbium compounds including the hydrides and fluorides YbH 1,8 and YbH 2,5 , YbF 2,33 , YbF 3 and the solid solution YbH 1,8 -nYbF 2,33 (1,75 ≤ n ≤ 1,95). All are anionic conductors. The hydride YbH 2,55 exhibits the best performance. Detailed correlations are established between anionic conduction and structural characteristics.

Determination de l'enthalpie standard de formation de l'hydrurofluorure de potassium magnesium KMgH2F

Abstract The standard enthalpy of formation of KMgH 2 F was determined on the basis of the measurement of the heat of the reaction KF + Mg + H 2 →KMgH 2 F. A calorimetric study was performed in a Calvet-type apparatus. The value found here (−806±4kJmol −1 ) is compared with a previous result obtained by another method (−762.6 ± 10kJmol −1 ).