On the structural and thermodynamic properties of the -hydrogen (, Ce, Nd and Sm) systems

Abstract

The (, Ce, Nd and Sm) intermetallic compounds were prepared and studied by means of x-ray powder diffraction. All compounds are single phase and exhibit the same hexagonal symmetry ( type; space group ) as do their prototype binaries. The interaction with hydrogen was also studied. It was found that all ternary intermetallics react readily and reversibly with hydrogen to form hydrides with high hydrogen contents of up to four hydrogen atoms per alloy formula unit. The pressure composition desorption isotherms were measured. The entropy, the enthalpy and the Gibbs free energy of formation have been extracted from the equilibrium plateau in the pressure-composition desorption isotherms. The hydrogen capacity and the equilibrium pressure of the -hydrogen systems were compared with the corresponding values for their aluminium analogues and with the values for the -hydrogen systems and briefly discussed. The hydride properties of gallium containing and aluminium containing compounds show great similarities whereby both series of ternary compounds form more stable hydrides and exhibit smaller hydrogen capacities than do the corresponding binaries.