Relationship between structure and sorption kinetic behaviour for ternary CeMX compounds
Résumé
The crystal structure and the hydrogenation behaviour of more than 10 ternary compounds based on cerium (i.e. CeMX with M=Mn, Ni, Cu and X=Al, Ga, In, Si, Ge, Sn) is presented. Most of the structures can be described as a stacking of [Ce6] trigonal prisms occupied by a M or a X atom. All these compounds form stable hydrides and the kinetic behaviour can be linked to the H insertion sites and to the structural changes upon hydrogenation. If no structural change is observed during the formation of the hydride and if H atoms occupy [Ce3M] tetrahedral sites, the reaction with hydrogen is fast. But if a structural change occurs during hydrogenation, then, the reaction takes place slowly. Particular behaviour is reported when H atoms occupy (i) [Ce4] tetrahedral sites (slow kinetics without structural change) and (ii) [Ce3Ni2] or [Ce3Si2] bipyramidal sites (high kinetics without a structural change).