No abstract available

[en] An equation of V/V₀=((B₀+bx)/B₀)^1/b for describing the unit-cell volume V at a composition x has been derived from 1/B_x=(1/V) (dV/dx), which represents the relative volume change with x with B₀(V₀) being the value of B_x(V) at x=0 and b the first derivative of B_x with respect to x (B_x=B₀+bx). It turned out that the equation could reproduce the experimental data for the Laves phase hydrides RMn₂H_x (R=Y, Gd, Tb and Dy), with different B₀ and/or b depending on the rare earth metal. Interestingly enough, the values of 1/B₀=(1/V) (dV/dx)_x=0 decreased as the lattice parameters of RMn ₂ increase, indicating that 1/B₀ should decrease as the hydrogen occupation sites (A ₂B ₂) in the cubic (C15) AB ₂ Laves phase compounds become more spacious with an increase in lattice parameters of RMn ₂. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The C15 Laves phase intermetallic YMn₂ and its deuterides containing 1.15, 2, 3.4 and 4 deuterium (D) atoms per formula unit (pfu) (the structure of YMn₂D₄ is rhombohedral whereas other three deuterides preserve the cubic C15 structure) were compressed up to 31 GPa by using diamond anvil cell (DAC). Parameters of equation of state (EOS) were derived for all phases investigated. The discontinuous change of bulk modulus under high pressure has been revealed for all samples investigated. Two deuterides, YMn₂D_1.15 and YMn₂D₂, decomposed reversibly under pressure into two phases: poor and enriched in deuterium

[en] Complete text of publication follows: The purpose of the current work was to synthesize and investigate the hydrogen storage properties of ternary alloys from RE-M-Mg systems (RE-rare earth metals, M - transition element such as Ni and Cu). Alloys based on magnesium are known to store high amount of hydrogen (up to 7.7 wt.%) reversibly. Mg₂Ni-based alloys offer also very high capacity (up to 4 wt.% H₂). This storage capacity coupled with a low price and reversibility suggests that magnesium and magnesium-based alloys could be advantageous for use in battery electrodes and gaseous - hydrogen storage systems. Therefore, Mg-based and Mg₂Ni-based materials were in the focus of our studies. The REMg₂Cu₉ ternary compounds (where RE - Y, La-Nd, Sm-Ho, Yb) [1] and REMg₂(CuNi)₉ alloys (where RE = La, Tb, Pr) were synthesised. Crystal structure determination and microstructural characterisation were performed. LaMg₂Cu₉, TbMg₂Cu₉, PrMg₂Cu₉, LaNi₅Cu₄Mg₂ and TbNi₃Cu₆Mg₂ were chosen for the investigation of hydrogen storage properties. TbMg₂Cu₉ and PrMg₂Cu₉ did not absorb hydrogen in pressure range 1 to 10 bar and at the ambient temperature. LaMg₂Cu₉ absorbs 3 H/f.u (1.004 wt%) under 100 bar and at 25 C. LaMg₂Cu₄Ni₅ absorbs 1.6 H/f.u (1.002 wt%) under 10 bar and at 25 C. Pressure - hydrogen concentration isotherm was measured. TbMg₂Ni₃Cu₆ absorbs 3 H/f.u (1.004 wt%) under 100 bar and at 25 C. All the samples needed to be activated by heat treatment under vacuum followed by several absorption - desorption cycles

No abstract available

[en] Rare earth orthovanadates, REVO₄, having the zircon structure, form a series of materials interesting for magnetic, optical, sensor, and electronic applications. Enthalpies of formation of REVO₄ compounds (RE=Sc, Y, Ce-Nd, Sm-Tm, Lu) were determined by oxide melt solution calorimetry in lead borate (2PbO.2B₂O₃) solvent at 1075 K. The enthalpies of formation from oxide components become more negative with increasing RE ionic radius. This trend is similar to that obtained for the rare earth phosphates. - Graphical abstract: Comparison of enthalpies of formation from oxides at 298 K for REVO₄ [this work] and REPO₄ compounds [S.V. Ushakov, K.B. Helean, A. Navrotsky, L.A. Boatner, J. Mater. Res. 16(9) (2001) 2623] vs. RE³⁺ ionic radius. Filled symbols indicate scheelite structure, open symbols zircon structure

[en] A hexagonal hydride of ZrCr₂H_x with a hydrogen concentration of x 5.75 was synthesized using high hydrogen pressure (5 kbar) at 100 deg. C for 72 h. The synthesized hydride is well characterized as regards structure and/or stability, as compared with cubic or hexagonal ZrCr₂ hydrides that are formed under conventional hydrogenation conditions

[en] A new phase YMn₂D₆ was synthesized by submitting YMn₂ to 1.7kbar deuterium pressure at 473K. According to X-ray and neutron powder diffraction experiments, YMn₂D₆ crystallizes in the Fm3-bar m space group with a=6.709(1)A at 300K. The Y and half of the Mn atoms occupy statistically the 8c site whereas the other Mn atoms are located in 4a site and surrounded by 6D atoms (24e). This corresponds to a K₂PtCl₆-type structure with a partially disordered substructure which can be written as [YMn]MnH₆. No ordered magnetic moment is observed in the NPD patterns and the magnetization measurements display a paramagnetic behavior. The study of the thermal stability by Differential Scanning Calorimetry and XRD experiments indicates that this phase decomposes in YD₂ and Mn at 625K, and is more stable than YMn₂H_4.5

[en] New deuterides of Laves phases: ErFe₂D₅, YFe₂D₅, ZrFe₂D_3.5 and ZrCo₂D₂, have been obtained by using of gaseous deuterium at high pressure. A new orthorhombic structure was found for ErFe₂D₅ and YFe₂D₅, while ZrFe₂D_3.5 and ZrCo₂D₂ were formed with a large expansion of the initial C15 cubic lattice. Formation of hydrides with high hydrogen concentration substantially changes the magnetic properties of ErFe₂ and YFe₂ but has no significant influence on the magnetization of ZrFe₂. The possibility of the formation of new deuterides (hydrides) in ZrCr₂ and YMn₂ has also been confirmed