Temperature and Impurity Induced Stabilization of Cubic HfV₂ Laves Phase

The stability of cubic HfV₂ $\left(Fd\overline{3}m\right)$ was investigated as a function of temperature as well as interstitially solved oxygen and hydrogen using density functional theory. Mechanical and energetic instability of pristine cubic HfV₂ is obtained in the ground state at 0 K, which is unexpected as it can readily be synthesized. Combined Debye–Grüneisen and electronic entropy calculations indicate that HfV₂ is stabilized with increasing temperature primarily as a result of lattice vibrations. In contrast, temperature-induced mechanical stabilization, considering the Born stability criteria, is achieved due to the electronic entropy. Interstitial incorporation of hydrogen and oxygen into the cubic structure contributes to the energetic and mechanical stabilization in the ground state for impurity concentrations as low as 1 at%, owing to strong ionic/covalent bond formation with the matrix atoms.