Theoretical Studies Of Carbon-based And Carbon-like Superhard Materials

As the main force of superhard materials,carbon-based and carbon-like superhard materials have the advantages of large adjustable range of components,diverse optional properties,and rich potential configurations.Therefore,the research on carbon-based and carbon-like superhard materials has become a major focus in the study of novel superhard materials.In this paper,the response of structural,elastic,electronic,hardness and thermodynamic properties of the carbon-based superhard material h-C₆and carbon-like superhard material t-BN under hydrostatic pressure and biaxial stress has been thoroughly studied by the use of density functional theory method that based on the first-principles.In addition,we used atomic substitution to obtain two novel monoclinic BC₃N structures from non-superhard structures.Through the simulation of Vickers hardness,we confirmed the superhard properties of all structures.Among them,the hardness of h-C₆ is up to 69.96 GPa,the hardness of m-BC₃N-1 is followed by 56.38 GPa,the hardness of t-BN is slightly lower at 55.5 GPa,and the hardness of m-BC₃N-2 is at least 52.96 GPa.Under pressure and compressive stress,the elastic constants and elastic modulus of h-C₆ and t-BN are strengthened,and the Vickers hardness also has the same trend,indicating that pressure and compressive stress have a positive adjustment effect on the properties of elasticity and hardness.In the discussion of electronic properties,the calculations based on hybrid functions show that several structures are indirect band gap materials when they are not stressed,and their band gap energy can be controlled by external forces.It is worth noting that m-BC₃N-2 will change from an indirect band gap to a direct band gap at a pressure of 30 GPa.In addition,the calculation of crystal sound velocity and Debye temperature also shows that h-C₆ and t-BN have potentially high thermal conductivity and can be maintained under external forces.Through theoretical research on the carbon-based h-C₆ and carbon-like t-BN,m-BC₃N structures,we have clarified the basic properties and external force response of these materials,and made predictions on their possible practical ways.The system results we obtained will also provide an important reference for further research on their other physical properties.