Lattice distortion, mechanical and thermodynamic properties of (TiZrHf)C and (TiZrHf)N ceramics

Although severe lattice distortion is one of the core effects of multicomponent materials, accurate quantitative description is still an open issue. In this paper, density functional theory (DFT) calculations based on special quasi-random structure (SQS) are used to investigate the lattice distortion of multicomponent (TiZrHf)C and (TiZrHf)N ceramics, and the influences on structural, mechanical, electronic and thermodynamic properties. The distortion in (TiZrHf)C and (TiZrHf)N is quantified by the average atomic displacement and the bond length distribution. Our results show that the distortion in (TiZrHf)N is greater than in (TiZrHf)C. Lattice distortion can improve thermodynamic stability while enhancing ductility at the expense of strength and hardness. Moreover, the influence of lattice distortion on thermal properties is further studied, suggesting that the distortion increases the vibrational entropy due to the high-temperature softening of the lattice, thereby increasing the total entropy and thermodynamic stability of ceramics. After distortion, the thermal expansion coefficient is obviously larger and the heat capacity CV and CP also increase, especially at low temperatures. Therefore, the present study is valuable for understanding and optimization of the comprehensive properties of multicomponent ceramics by tuning the lattice distortion effect.