Effects of vacancies on structural, electronic, mechanical, and thermodynamic properties of C40-VSi₂

ABSTRACT

In our work, to figure out the effects of V and Si vacancies on formation energies, elastic properties, phonon dispersions, electronic structures, and thermodynamic properties of VSi₂, we used first-principles calculations. VSi₂ with V and Si vacancies are dynamically and thermodynamically stable from the calculated formation energies and phonon dispersions. Moreover, VSi₂ with V and Si vacancies are mechanically stable certified by single-crystal elastic constants. The presence of different atomic vacancies can weaken the bond strength of V–Si and Si–Si bonds, and eventually leads to the decreasing phase stability and elastic modulus, but can increase elastic anisotropy and ductileness. Finally, thermodynamic properties, including Debye temperature, sound velocities, and directional sound velocities, of perfect VSi₂ and VSi₂ with different vacancies are calculated.

Highlights

• Based on the calculated vacancy formation energies and phonon dispersions, the perfect VSi₂ and VSi₂ with different vacancies are thermodynamically and dynamically stable.

• The vacancies can reduce the thermodynamical stability of VSi₂, VSi₂ with V vacancies are more stable than those with Si vacancies, and among VSi₂ with vacancies, VSi₂ with V-Va1 is the most stable.

• The perfect VSi₂ and VSi₂ with different vacancies are brittle, and the atomic vacancies can improve the ductility of VSi₂ slightly, but can weaken the elastic modulus.

• The order of elastic anisotropy is Si-va3 > Si-va1 > Si-va2 > V-va2 > V-va1 > perfect VSi₂.

• The Si–Si and V–Si bonds are broken after Si or V atoms removed, resulting in the decreasing bond strength in VSi₂ with vacancies, and eventually leading to the lower phase stability and elastic moduli of VSi₂ with vacancies compared to the perfect VSi₂.

• The calculated sound velocities also show anisotropy.

KEYWORDS:

• First-principles calculations
• VSi₂
• vacancy
• elastic properties
• thermodynamic properties

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Rare and Precious Metal Materials Genome Engineering Project of Yunnan Province [grant number 202002AB080001] and Yunnan Ten Thousand Talents Plan Young & Elite Talents Project [grant number YNWR-QNBJ-2018-044].