Phase transformation and hydrogen storage properties of LaY2Ni10.5 superlattice alloy with single Gd2Co7-type or Ce2Ni7-type structure

•The single-phase LaY2Ni10.5 alloy with superlattice structure was firstly prepared.•The LaY2Ni10.5 alloy adopts the hexagonal structure at high annealing temperatures.•The hexagonal LaY2Ni10.5 alloy demonstrates higher structural stability than the rhombohedral polymorph during charging-discharging cycles. The structural evolution of as-cast LaY2Ni10.5 multi-phase alloy with the annealing temperature has been investigated, and the single-phase alloy with rhombohedral Gd2Co7-type or hexagonal Ce2Ni7-type structure was firstly prepared. It is found that the rhombohedral structure is more stable than the hexagonal polymorph at the low temperature, which is reversed at the high annealing temperature. Structural refinement indicates that Y atoms preferably substitute La in the [A2B4] subunit of both hexagonal and rhombohedral superlattice structures. Compared with the rhombohedral polymorph, the hexagonal phase possesses a relatively smaller volume of [A2B4] subunit and thus demonstrates higher structural stability during the hydrogen charging-discharging cycling. This work offers the guideline for the preparation process and composition optimization of single-phase rare earth-based A2B7-type alloys for nickel-metal hydride battery applications.