Thermodynamic properties of the RENiIn hydrides with RE = 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 RE 3Ni 2 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: Δ H H =−38.1 ± 3.2 kJ mo l H − 1 , Δ S H = −79.6 ± 5.0 J K −1 mo l H − 1 for RE = La; Δ H H =−26.0 ± 0.8 kJ mo l H − 1 , Δ S H =−66.5 ± 1.5 J K −1 mo l H − 1 for RE = Ce; Δ H H = −15.3 ± 1.1 kJ mo l H − 1 , Δ S H = −42.3 ± 2.2 J K −1 mo l H − 1 for RE = Pr; Δ H H = −19.4 ± 0.6 kJ mo l H − 1 , Δ S H = −56.0 ± 1.4 J K −1 mo l H − 1 for RE = Nd.