First-Principles Study On Physical Properties Of Binary Metal Silicides

Up to now,transition metal silicides,as a kind of high temperature structural materials,have attracted extensive attention due to their excellent high temperature properties.For high-temperature structural materials,vacancy defects play a crucial role in their mechanical properties as a consequence of the thermal activation effect in high-temperature environments.However,the formation of vacancies and their mechanisms remain a great challenge for high-temperature applications.Therefore,it is of great significance to explore the correlation between vacancies and properties.In order to systematically investigate the effect of vacancy defects on the mechanical properties and electronic structure of binary metal silicides(TaSi₂,Ta₅Si₃and Mo₅Si₃),the vacancy formation energy,formation enthalpy,elastic modulus,anisotropy,hardness,ductility,and electronic structure of binary metal silicides(TaSi₂,Ta₅Si₃and Mo₅Si₃)have been calculated using first-principles calculations.The correlation between vacancy mechanisms and elastic properties is discussed in detail.The vacancy defect model in Mo₅Si₃is compared with the oxygen atom occupation model.The results show that:(1)Based on the vacancy formation energy it can be concluded that TaSi₂is more inclined to form Ta vacancies.The presence of vacancy defects,although weakening the deformation resistance and elastic stiffness of TaSi₂,causes a brittle-ductile transition,which is caused by the disruption of the original electronic equilibrium state,weakening the local hybridization between the charges.(2)Thermodynamic data and phonon dispersion indicate that the Ta vacancies in Ta₅Si₃have better stability in comparison to the Si vacancies.Although the presence of vacancy defects weakens the deformation resistance and hardness of Ta₅Si₃,it improves the intrinsic brittleness of Ta₅Si₃.Notably,the presence of Ta_-Va1vacancy defects contributes to the brittle-ductile transition of Ta₅Si₃.(3)In Mo₅Si₃,both the vacancy defect models and the oxygen atom occupation models are in steady states.The presence of vacancy defects improves the toughness of Mo₅Si₃to some extent,but the introduction of oxygen atoms in the Si_-Va2vacancy sites causes Mo₅Si₃to exhibit the most excellent toughness properties due to the formation of weaker O-Mo bonds between O and Mo atoms.