Thermodynamic and structural properties of LaNi 5−xMn x compounds and their related hydrides

Abstract

Metallurgical, structural and thermodynamic properties of LaNi 5− x Mn x compounds and their related hydrides were determined. The limit of existence of pseudo-binary intermetallic compounds with the hexagonal structure P6/ mmm is x = 2.2 at 800 °C. The lattice parameters and the cell volume increase with increasing manganese content, the change being linear up to x = 1.5. The hydrogen absorption and desorption isotherms were determined by an incremental method between 25 and 200 °C. The partial substitution of nickel by manganese involves a large decrease of the plateau pressure which is proportional to the manganese content. Neutron diffraction measurements show that manganese atoms mainly occupy the 3g sites in the LaNi 5 structure and that the deutendes retain the same structure in which, although deuterium atoms are widely distributed on interstitial sites, there is a preference for the 6m and 12n sites.