Thermodynamic properties of the RENiIn hydrides with REÂ =Â La, Ce, Pr and Nd

The Pressure-Composition-Temperature diagrams for the RENiIn-H systems (RE = La, Ce, Pr, Nd) were determined by a volumetric method. The P-C isotherms show a two-phase (β + γ) region where a transformation from a single to a double H occupancy of the trigonal bipyramidal RE3Ni2 site takes place. The β-hydride was stable at pressures and temperatures applied in the present work. Thermodynamic properties of hydrogen in RENiIn intermetallic compounds strongly depend on the RE elements: ΔHH =−38.1 ± 3.2 kJ molH−1, ΔSH = −79.6 ± 5.0 J K−1 molH−1 for RE = La; ΔHH =−26.0 ± 0.8 kJ molH−1, ΔSH =−66.5 ± 1.5 J K−1 molH−1 for RE = Ce; ΔHH = −15.3 ± 1.1 kJ molH−1, ΔSH = −42.3 ± 2.2 J K−1 molH−1 for RE = Pr; ΔHH = −19.4 ± 0.6 kJ molH−1, ΔSH = −56.0 ± 1.4 J K−1 molH−1 for RE = Nd.