Theoretical exploring superior stiffness and strength of ternary carbosilicides TM0.5Si0.5C (TM=Cr, Mo, W) with excellent stability for extreme conditions

The advantages of multi-element carbides with combination of outstanding physical properties such as high hardness, high melting points, good resistance to corrosion, oxidation are attracting considerable interests due to their potential applications at extreme conditions. Herein, a new type of hexagonal ternary transition metal carbosilicides TM 0.5 Si 0.5 C (TM=Cr, Mo, W) possessing high-temperature stability and improved mechanical properties like hardness, toughness and strengths relative to the well-known SiC are firstly reported and systematically studied using first-principles calculations. Employing a hybrid approach that integrates ab initio molecular dynamics (AIMD) simulations with lattice dynamics, we determined the renormalized phonon spectra at high temperatures, confirming their dynamic and thermodynamic stabilities up to 2500 K. Utilizing a refined approach within density-functional AIMD simulations, we also investigate the ideal strengths at different temperatures, revealing these compounds exhibit large tensile strengths up to 35 GPa even at 2000 K. Electronic analysis indicates that the orbital hybridizations of TM- d and C- p as well as Si- p and C- p play the key role in determining the exceptional mechanical properties. Correlating the current results with our prior findings, we formulate a general principle guiding the design of a new class of hard multi-element ceramic compounds with superior mechanical properties and high-temperature stability.