First Principles Study Of Mechanical,Electrical And Optical Properties Of TiC And Its Doped Compounds

As a typical transition metal carbide,titanium carbide（TiC）has a wide range of applications in alloys,ceramics,coatings,and other fields due to its excellent physical and chemical properties.Based on density functional theory,this paper conducts first principles calculations to explore the effects of high pressure on the mechanical,electrical,and optical properties of TiC,and to explain the mechanism.By constructing a structural model of TiC_（1-x）N_x,Ti_（1-y）Al_y,and Ti_nAl_（1-n）C_mN_（1-m）doped systems,the changes in the mechanical,electrical,and optical properties of TiC caused by monoatomic,diatomic,and different atomic and doping concentrations were discussed,and the following conclusions were obtained:1.In this paper,the lattice constant of TiC is 4.331?obtained by structural optimization,and the phase transition from Na Cl structure to Cs Cl structure is measured for TiC under the pressure of 571.6 GPa.The mechanical and dynamic stability of TiC under 0-571.6 GPa pressure was verified using the elastic constant(C_ij)and phonon spectrum,respectively.In addition,the pressure effect has a great influence on the mechanical,electrical and optical properties of TiC,which will increase the elastic modulus,elastic anisotropy and hardness of TiC;the pressure effect also enhances the covalency and decreases the metallicity of TiC;meanwhile,it will increase the dielectric function,reflectivity,photoconductivity and absorption of TiC.2.In this work,two systems of TiC_（1-x）N_x（x=0,0.25,0.5,0.75）and Ti_（1-y）Al_y（y=0,0.5,0.75）were constructed by substitution doping,and the effects of different single-atom doping and their doping concentrations on the mechanical,electrical and optical properties of the systems were investigated.The calculated results show that N atom doping improves the mechanical properties of the system;enhances the covalency of the system;but decreases the conductivity,reflection,and refractive ability of the system.Although Al atom doping makes the mechanical properties of the system much worse,it enhances the ductility of the system and makes Ti_（1-y）Al_yperform well in the field of composite coatings;and Al atom doping improves the metallicity and electrical conductivity of the system.3.The effects of co doping of N and Al atoms on the properties of the system were investigated.The effects of different atoms and doping concentrations on the properties of the system were discussed by fixing the proportion of metallic or non-metallic atoms and changing the proportion of another type of atom.Analysis of quaternary structure data shows that under fixed metal atom ratios,increasing the doping concentration of N atoms optimizes the mechanical properties such as elastic modulus,hardness,and structural covalence of the system,but decreases the metallicity,conductivity,and reflective,photoconductive,and refractive abilities of the system.The comparison of the proportion of fixed non-metallic atoms shows that Al atoms in the quaternary structure still have a negative impact on the mechanical properties of the system,but will improve the ductility,metallicity,and electrical conductivity of the system.