Experimental investigation and thermodynamic assessment of La-Y-Ni ternary system in Ni-rich corner

La-Y-Ni alloys exhibit high discharge capacity due to the formation of AB(3-3.8)-type (A = La, Y; B = Ni) intermetallic compounds. However, the stable composition and temperature range for this type of phase are rarely reported, which restrains the development of La-Y-Ni hydrogen storage alloys with stable structure and high capacity. This paper focuses on the phase equilibria of the La-Y-Ni ternary system in Ni-rich corner. The phase constitution, microstructure, and equilibrated composition were experimentally determined at 1273 and 1148 K using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The solubilities of La and Y in the binary compounds were measured. Two ternary compounds, 3R-LaY2Ni9 with the structure of PuNi3 type and La0.5Y0.5Ni5 with the structure of CaCu5 type, existed at both temperatures. Based on the experimental data, the thermodynamic description of La-Y-Ni system was assessed by Calculation of Phase Diagram method. The calculated isothermal sections agree with the experimental data. The thermodynamic database is helpful for the design of La-Y-Ni hydrogen storage alloys.

Automated summary

This study experimentally investigated the phase equilibrium of the La-Y-Ni ternary system in the Ni-rich corner and assessed its thermodynamic properties using calculation methods. The results of this study are of great significance for the design of La-Y-Ni hydrogen storage alloys.