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

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 [A(2)B(4)] subunit of both hexagonal and rhombohedral superlattice structures. Compared with the rhombohedral polymorph, the hexagonal phase possesses a relatively smaller volume of [A(2)B(4)] 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 A(2)B(7)-type alloys for nickel-metal hydride battery applications. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study reveals that the as-cast LaY2Ni10.5 multi-phase alloy can be prepared into single-phase alloys with different structures by annealing at different temperatures. Y atoms preferentially substitute La in the [A(2)B(4)] subunit of hexagonal and rhombohedral superlattice structures, affecting the structural stability of the alloy.