First-principles Study On Physical Properties Of Transition-metal Silicides

In recent years,ternary transition-metal silicides are widely used as high temperature materials due to their excellent physical and chemical properties.Such as the sharp leading edges materials,high temperature reusable surface materials of hypersonic cruise vehicles and surface coatings for ultra-high-temperature ceramic composites.But the inherent brittleness hinders their industrial applications.It is necessary to investigate and clarified their physical properties for further developing and using the ternary transition-metal silicides high temperature materials.So far,the physical properties of ternary transition-metal silicides TM₅BSi₃（TM=Zr,Nb,Ta,Mo and W）have not been systematically investigated.In this paper,five silicides were designed based on hexagonal Hf₅BSi₃,the physical properties such as the phase stability,mechanical,anisotropy,electronic,optical and thermodynamic properties of TM₅BSi₃（TM=Zr,Nb,Ta,Mo and W）were explored by the first-principles calculations method.Due to the vacancy defects possess an important influence on physical properties of materials,this work further designed four different atomic vacancy defects and discussed the effects of them on the physical properties of Hf₅BSi₃ and Cr₅BSi₃.The results indicate that TM₅BSi₃ compounds possess the thermodynamical and dynamical stability.Mo₅BSi₃ and W₅BSi₃ are malleable.Optical analysis shows they express good photoconductivity.The data of lattice vibration and thermodynamic parameters indicate that the Hf₅BSi₃ and Cr₅BSi₃ with different atomic vacancies possess structural stability.The different atomic vacancies weaken the shear and volume deformation resistance of Hf₅BSi₃and Cr₅BSi₃,but change the mechanical properties of them and improve their brittle-ductile behavior.Especially,the existence of B vacancy makes Cr₅BSi₃ change from brittleness to ductility.The structural stability and mechanical behavior of Hf₅BSi₃ and Cr₅BSi₃ with different atomic vacancies were analyzed by the density of states and electron density difference.Thermodynamic parameters indicate that these vacancy defects have a certain effect on the thermodynamic properties of Hf₅BSi₃ and Cr₅BSi₃ at elevated temperature.