Hydrogen absorption-desorption characteristics of the LaNi5Sn intermetallic compound

The pressure-composition-temperature (P-C-T) relations in the LaNi5Sn-H system were measured volumetrically at temperatures between 258 and 423 K. Two hydride phases, β-LaNi5SnH2 and γ-LaNi5SnH3 are formed in this system in addition to the α-solid solution with a limiting H content of 0.3 H atoms per formula unit. The calculated work loss due to hysteresis is rather small, 112 J (mol H)-1 at 298 K. The partial molar enthalpy and entropy calculated for the formation of the β-LaNi5SnH2 are -18.5±0.8 kJ (mol H)-1 and -53.7±2.3 J (K mol H)-1, respectively. An advanced van der Waals lattice gas model was applied to fit the isotherms. The critical temperature of the LaNi5SnH2 equals TC=421±17 K