| In this paper,the first-principles calculation method of density functional theory is used to systematically study a series of properties of 211 phases M2SnC(M=Ti,V,Zr,Nb,Hf,Ta)ternary layered carbide in the range of 0 to 50 GPa.Firstly,the structural properties(cell parameter constants),mechanical properties(elastic constants,elastic modulus,plasticity and hardness,elastic anisotropy),lattice dynamics,electronic properties(energy band structure and electron state density)of M2SnC(M=Ti,V,Zr,Nb,Hf,Ta)of each compound under 0 GPa were calculated.Secondly,the effects of pressure on the structural properties,mechanical properties and electronic properties of M2SnC(M=Ti,V,Zr,Nb,Hf,Ta)compounds were calculated.(1)The equilibrium cell parameters and elastic constants of M2SnC(M=Ti,V,Zr,Nb,Hf,Ta)compounds were calculated under the condition of 0 GPa.The calculated results are basically consistent with the experimental values and other theoretical values in the existing literature,indicating that the calculation method used has certain feasibility.As the atomic radius of M transition metal increases,lattice constants a and c,lattice volume V and theoretical density all increase,indicating that the M2SnC phase compounds studied tend to be stable with the increase of atomic radius.The Born mechanical stability criterion and lattice dynamics verify the mechanical stability of these compounds,which belong to anisotropic materials.Ta2SnC has strong resistance to volume deformation and chemical bonds,and its machinability coefficient is also the highest.V2SnC has the lowest shear modulus,which indicates that its friction coefficient is low.V2SnC has excellent thermal shock resistance.Ta2SnC is a ductile material,while other compounds are brittle materials.The cauchy pressures of M2SnC phase compounds are all negative,indicating that these compounds have strong covalent bonds.The electron properties prove that all these compounds have metallic properties,and the strength of M-Sn bond and M-C bond increases with the number of valence electrons.(2)In order to understand the influence of pressure on the structural properties,mechanical properties and electronic properties of M2SnC(M=Ti,V,Zr,Nb,Hf,Ta)compounds.Therefore,the added pressure of M2SnC(M=Ti,V,Zr,Nb,Hf,Ta)compounds was calculated.The pressure range was 0～50 GPa,the added pressure was hydrostatic pressure and the added pressure was added at an interval of 10 GPa.The calculation results show that:in the range of 0～50 GPa,with the lattice parameters(a/ao,c/c0)and the relative volume(V/V0)of these compounds decrease continuously,while the internal parameter Z of the lattice increases with the increase of pressure.In addition,a/a0 decreases faster and c/c0 decreases slower,which indicates that these compounds are more easily compressed in the direction of a-axis and also reflect anisotropy.According to the Bonn mechanical stability criterion,it can be judged that these compounds have mechanical stability within the pressure range of 0～50 GPa.On the whole,all elastic constants increase with the increase of pressure,and C11 and C33 are more obvious as the pressure changes,which indicates that the pressure has effect on enhancing the linear compression resistance of the a-axis and c-axis is more obvious.The volume modulus B,shear modulus G,young’s modulus E,B/G poisson ratio,and vickers hardness Hv all increase with the increase of pressure,indicating that the increase of pressure can improve the deformation resistance,shear compression resistance,stiffness and hardness of the compound;The increase of B/G and poisson’s ratio indicates that appropriate pressure can improve the plasticity of the compound;With the increase of pressure,the electron density N(Ef)at Fermi energy level decreases,so that the stability and hardness of the compound increase. |
