First-Principles Insights into the Site Occupancy of Ta-Fe-Al C14 Laves Phases

Abstract

This study investigates the site occupancy preferences of Al in Ta(Fe$_{1-x}$Al$_x$)$_2$ Laves phases using first-principles calculations, covering Al concentrations from 0 to 50 at.\%. Al atoms exhibit a strong preference for $2a$ Wyckoff sites, with configurations becoming more energetically favorable as these sites reach full occupancy at high Al concentrations. Magnetic configurations were explored, revealing that anti-ferromagnetic ordering is the most favorable at ground states. A metastable defect phase diagram based on the chemical potential of Al was constructed to map site occupancy preferences, where Ta$_4$Fe$_6$Al$_2$ and Ta$_4$Fe$_2$Al$_6$ exhibit the widest chemical potential windows. The correlation between lattice distortions and site occupancy was examined, demonstrating that symmetric Al distributions enhance structural preference. These findings offer insights into the structural motifs of the Ta-Fe-Al system, providing a foundation for future investigations on structure-property relationships.