Abstract
The stability of cubic HfV2 (Fd3m) 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.
Highlights
HfV2 exhibits an exceptional combination of properties including superconductivity [1,2,3,4], low temperature structural transformations [4,5,6], high hydrogen storage capacity [7,8,9,10] and anomalous elasticity, namely increasing elastic moduli with temperature [1,11,12]
The ground state stability of cubic HfV2 was investigated in terms of its energetic stability, evaluated based on the energy of formation E f, and its mechanical stability, which can be analyzed based on the calculated elastic constants compared to the Born stability criteria [33]
In order to support the reliability of this result, additional calculations using local density approximation (LDA) were performed leading to a positive E f of 20.4 meV/atom
Summary
HfV2 exhibits an exceptional combination of properties including superconductivity [1,2,3,4], low temperature structural transformations [4,5,6], high hydrogen storage capacity [7,8,9,10] and anomalous elasticity, namely increasing elastic moduli with temperature [1,11,12]. In addition to the pronounced effect of temperature on the stability of cubic C15 HfV2, real intermetallic compounds may exhibit H and O impurities due to their availability in atmosphere, and presence in most production processes, in combination with the high hydrogen storage capacity of HfV2 [7,8,9,10] and the affinity for oxygen of the elemental constituents [18,19,20,21]. While some report that the cubic HfV2 structure exhibits negative energies of formation of −15.7 [14] and −18.0 meV/atom [15]. We systematically studied the effect of temperature as well as impurities of H and O on the stability of cubic C15 HfV2 using ab initio calculations. We examined how the ground state stability is affected by interstitially dissolved H and O impurities in cubic C15 HfV2
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
