Different cerium valence transitions observed by hydrogenation of the ternary germanides CeRhGe and CeIrGe - structure, physical properties and chemical bonding

Bernard Chevalier (1) , Etienne Gaudin (1) , Adel F. Al Alam (1) , Samir F. Matar (1) , François Weill (1, 2) , Birgit Heying (3) , Rainer Pöttgen (3)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 Centre de Ressources en Microscopie Electronique et Microanalyse
3 Institut für Anorganische und Analytische Chemie

The ternary germanides CeRhGe and CeIrGe which crystallize in the orthorhombic TiNiSi-type structure, absorb hydrogen at 523 K. X-Ray powder diffraction and transmission electron microscopy indicate that the hydrides CeRhGeH1.8 and CeIrGeH1.8 adopt the hexagonal ZrBeSi-type structure. Magnetization, electrical resistivity and thermoelectric power measurements reveal that these hydrides are intermediate-valence compounds. An unusual transition from antiferromagnetic to spin fluctuation behavior occurs upon hydrogenation of CeRhGe, while on the contrary, CeIrGeH1.8 presents a Kondo temperature of 285 K smaller than that observed for CeIrGe (610 K). In order to explain these opposite valence transitions, the electronic structures of the hydrides have been selfconsistently calculated within the local spin density functional theory (LSDF). The structures are compared to those reported previously by us for CeRhGe and CeIrGe.

Mots clés: Hydrogenation; Structural transition; Intermediate-valence compounds; Electronic structure calculation

Domaines: Matériaux

Bernard Chevalier, Etienne Gaudin, Adel F. Al Alam, Samir F. Matar, François Weill, et al.. Different cerium valence transitions observed by hydrogenation of the ternary germanides CeRhGe and CeIrGe - structure, physical properties and chemical bonding. Zeitschrift fur Naturforschung B, 2008, 63 (6), pp.685-694. ⟨10.1515/znb-2008-0615⟩. ⟨hal-00283172⟩