Site-dependent, chemically selective, and concentration sensitive impurity-driven stabilization of β-W

Abstract

The metastable β phase of tungsten (β-W), which adopts the A15 crystal structure, is frequently observed in impurity-rich environments despite its lower stability relative to α-W. The atomistic mechanisms responsible for this stabilization, however, remain unclear. Here, density functional theory (DFT) calculations are used to investigate the structural, energetic, and electronic effects of vacancies and substitutional impurities (H, N, O, and F) in β-W and compare them with α-W. Defect formation energies, cohesive energies, and Bader charge analysis reveal that vacancies alone do not stabilize β-W. In addition, substitutional impurities exhibit strong site-dependence within the A15 lattice, preferentially occupying the Face site. The stabilization effect also depends on the impurity element, with O producing the strongest stabilization of β-W relative to α-W. Calculations for the low-concentration case further indicates that stabilization by impurities is concentration-dependent.