Tuning Stability of AB3-Type Alloys by Suppressing Magnetism

TL;DR

This study investigates how suppressing magnetism in AB3-type alloys enhances their stability and hydrogen storage capacity, using first-principles calculations and simulations to identify compositions with optimal properties.

Contribution

It demonstrates that controlling magnetism through transition-metal substitution improves stability and gravimetric density in AB3 alloys for hydrogen storage.

Findings

Magnetism correlates with formation energy and stability.

Y substitution suppresses magnetism in Mg-rich alloys.

CaMg2Ni9 achieves high capacity (3.32 wt%) with reversibility.

Abstract

Hydrogen is a promising clean energy carrier, yet effective and reversible storage remains challenging. AB3-type intermetallic alloys are promising for solid-state hydrogen storage due to intermediate thermodynamic stability and rapid hydrogen uptake. Optimizing stability and gravimetric density is hindered by competing thermodynamic and magnetic effects. Here, we analyze AB3 compounds (A = Ca, Y, Mg; B = Co, Ni) and ternary alloys CaxYyMg1-x-yB3 using first-principles calculations and Monte Carlo simulations. We find a direct correlation between formation energy and total magnetic moment that dictates alloy stability, explaining the trade-off in hydrogen storage. In Co-rich systems with large lattice volumes, formation energy rises with magnetization, showing magnetism as the dominant factor. Mg-rich compositions achieve high gravimetric densities, but strong magnetism destabilizes the system, requiring Y substitution to suppress magnetic moments. Replacing Co with Ni weakens magnetism: YNi3 is nonmagnetic, while CaNi3 and MgNi3 are weakly polarized, allowing thermodynamic stability across compositions. Notably, CaMg2Ni9 combines high theoretical capacity (3.32 wt%) with good reversibility. Mg-rich Ni-based alloys are predicted to offer negative formation energies with the highest gravimetric densities (up to 3.40 wt%). These results show that controlling magnetism via transition-metal substitution is key to overcoming the stability-capacity trade-off in AB3 hydrogen storage materials.