Rare earth metal rich magnesium compounds <i>RE</i><sub>4</sub>NiMg (<i>RE</i>=Y, Pr–Nd, Sm, Gd–Tm, Lu)—Synthesis, structure, and hydrogenation behavior
Langue
en
Article de revue
Ce document a été publié dans
Journal of Solid State Chemistry. 2009, vol. 182, n° 2, p. 229-235
Elsevier
Résumé en anglais
The rare earth metal rich compounds <i>RE</i><sub>4</sub>NiMg (<i>RE</i>=Y, Pr–Nd, Sm, Gd–Tm, Lu) were synthesized from the elements in sealed tantalum tubes in an induction furnace. All compounds were investigated by X-ray ...Lire la suite >
The rare earth metal rich compounds <i>RE</i><sub>4</sub>NiMg (<i>RE</i>=Y, Pr–Nd, Sm, Gd–Tm, Lu) were synthesized from the elements in sealed tantalum tubes in an induction furnace. All compounds were investigated by X-ray diffraction on powders and single crystals: Gd<sub>4</sub>RhIn type, space group <i>F</i>4¯3<i>m</i>, <i>Z</i>=16, <i>a</i>=1367.6(2) pm for Y<sub>4</sub>NiMg, <i>a</i>=1403.7(3) pm for Pr<sub>4</sub>NiMg, <i>a</i>=1400.7(1) pm for Nd<sub>4</sub>NiMg, <i>a</i>=1386.5(2) pm for Sm<sub>4</sub>NiMg, <i>a</i>=1376.1(2) pm for Gd<sub>4</sub>NiMg, <i>a</i>=1362.1(1) pm for Tb<sub>4</sub>NiMg, <i>a</i>=1355.1(2) pm for Dy<sub>4</sub>NiMg, <i>a</i>=1355.2(1) pm for Ho<sub>4</sub>NiMg, <i>a</i>=1354.3(2) pm for Er<sub>4</sub>NiMg, <i>a</i>=1342.9(3) pm for Tm<sub>4</sub>NiMg, and <i>a</i>=1336.7(3) pm for Lu<sub>4</sub>NiMg. The nickel atoms have trigonal prismatic rare earth coordination. These Ni<i>RE</i><sub>6</sub> prisms are condensed via common edges to a three-dimensional network which leaves voids for Mg<sub>4</sub> tetrahedra and the <i>RE</i>1 atoms which show only weak coordination to the nickel atoms. The single crystal data indicate two kinds of solid solutions. The <i>RE</i>1 positions reveal small <i>RE</i>1/Mg mixing and some compounds also show Ni/Mg mixing within the Mg<sub>4</sub> tetrahedra. Y<sub>4</sub>NiMg and Gd<sub>4</sub>NiMg have been tested for hydrogenation. These compounds absorb up to eleven hydrogen atoms per formula unit under a hydrogen pressure of 1 MPa at room temperature. The structure of the metal atoms is maintained with only an increase of the lattice parameters (Δ<i>V</i>/<i>V</i>≈22%) if the absorption is done at <i>T</i><363 K as at higher temperature a decomposition into <i>RE</i>H<sub>2</sub>–<i>RE</i>H<sub>3</sub> hydrides occurred. Moreover, the hydrogenation affects drastically the magnetic properties of these intermetallics. For instance, Gd<sub>4</sub>NiMg exhibits an antiferromagnetic behavior below <i>T<sub>N</sub></i>=92 K whereas its hydride Gd<sub>4</sub>NiMgH<sub>11</sub> is paramagnetic down to 1.8 K.< Réduire
Mots clés en anglais
Magnesium
Intermetallics Crystal chemistry
Hydrogenation
Origine
Importé de halUnités de recherche