Thermodynamic characteristics of the Al- and Cu-doped NdNiIn hydrides

The Pressure-Composition-Temperature (P-C-T) relationships in the NdNiIn-based Cu- and Al-containing Nd(Ni1−xCux)(In1−yAly)-H systems were measured volumetrically in the temperature range of 298-348 K. The P-C-T diagrams show clear plateaux regions indicating a formation of two hydride phases, β- (∼ 0.6 at. H/f.u.) and γ- (1.3-1.5 at. H/f.u.) hydrides. The β-hydride is rather stable and does not decompose at hydrogen pressures above 10−3 MPa within the applied range of temperatures. The substitutions cause significant modifications of the P-C-T diagrams. These changes proceed differently for the Cu- and Al-containing systems. The relative partial molar thermodynamic properties for the studied system are: ΔHH=−19.4±0.6  kJ (molH)−1, ΔSH=−56.0±1.4  J (K⋅molH)−1 for NdNiIn-H; ΔHH=−22.6±1.6  kJ (molH)−1, ΔSH=−68.8±3.6  J (K⋅molH)−1 for NdNi0.98Cu0.02In-H; ΔHH=−23.5±1.3  kJ (molH)−1, ΔSH=−72.2±3.1  J (K⋅molH)−1 for NdNiIn0.95Al0.05-H systems.