Study On Physical Properties Of Binary And Ternary Transition Metal Boride Based On First Principles

In the past decades,binary and ternary transition metal borides have attracted extensive attentions.Transition metal boride usually have strong wear resistance,high hardness and strength,and good flame retardancy and heat resistance.According to these properties,transition metal borides can be used as mechanical cutting materials to ensure a good surface finish,as well as high temperature creep resistance materials.Among these transition metal dodecaborides（TMBs）,the transition metal dodecaboride(TMB₁₂)shows outstanding mechanical properties because of the high boron concentrations and 3D B-B covalent network.However,dodecaboride(TMB₁₂)exhibit the notable shortcomings,such as the brittleness and low thermal stability,which limits their applications in many fields.In this work,the structural,elastic,electronic and thermodynamic properties of six binary and ternary transition metal borides(Sc B₂,Sc B₁₂,Sc₃In B,Sc₃Pb B,Sc₃Sn B,and Sc₃Tl B)have been studied theoretically using the first principles method.In addition,the influence of the doping of transition metal TM（TM=Ti,Zr,Hf）and the pressure of 0-100 GPa on the elastic properties,brittle ductile transition and thermodynamic properties of transition metal dodecaboride Sc B₁₂ and YB₁₂ was studied by the first principles calculation method.We hope to improve the performance of dodecaborides to make them widely used in various industry.The results indicate that:（1）Sc B₂,Sc B₁₂,Sc₃In B,Sc₃Pb B,Sc₃Sn B,Sc₃Tl B all have thermodynamical and dynamical stability.According to Poisson’s ratio v and G/B,several borides show brittle behavior.Anisotropy is analyzed through the three-dimensional surface structure and two-dimensional projection of Young’s modulus,and Sc B₁₂ has the highest elastic anisotropy.（2）The formation enthalpy and phonon frequencies confirm that TM-doped models show the structural stability.The transition metal TM-doped weaken the elastic hardness of Sc B₁₂ and YB₁₂,but well improve the brittle behavior of Sc B₁₂and YB₁₂.The anisotropy of TM-doped models was illustrated by Young’s modulus three-dimensional surface constructions.The Debye temperature of TM-doped model is greater than that of parent Sc B₁₂ and YB₁₂.It indicates that the TM-doped increases the thermal stability of parent Sc B₁₂ and YB₁₂.（3）The parent Sc B₁₂ and YB₁₂ are brittle at 0 GPa.With the increase of pressure,the brittleness of parent Sc B₁₂ and YB₁₂ decreases.Sc B₁₂ transforms from brittle material to ductile material when the pressure exceeds 80 GPa.The Debye temperature of Sc B₁₂ and YB₁₂ increases with increasing pressure at a given temperature.Pressure increases the elastic anisotropy of Sc B₁₂ and YB₁₂.The results of C_ij show that Sc B₁₂ and YB₁₂ are mechanically stable under the pressure of 0-100 GPa.The elastic modulus of Sc B₁₂ and YB₁₂significantly increased,indicating that the increase of pressure improved the mechanical properties of Sc B₁₂ and YB₁₂.