First-principles investigation of equilibrium phase, mechanical and thermodynamic properties of the Nowotny TM5Si3C ternary phase

Although the TM-Si-C ternary compounds are potential high-temperature ceramics, the equilibrium phase, mechanical and thermodynamic properties of Nowotny phase (NP) are still unclear. Here, the structural stability, mechanical and thermodynamic properties of the TM 5 Si 3 C Nowotny phase (NP) are studied by the first-principles calcualtions. Four TM 5 Si 3 C ternary phases (TM = Mo, Nb, W and Ta) are considered. It is found that the equilibrium structure of the Nowotny phase (NP) is a TM 5 Si 3 C. In particular, the Mo 5 Si 3 C, Nb 5 Si 3 C, W 5 Si 3 C and Ta 5 Si 3 C are firstly predicted. Nb 5 Si 3 C has better thermodynamic stability in comparison to the other TM 5 Si 3 C. Furthermore, the calculated elastic properties show that four TM 5 Si 3 C not only exhibit similar strength in comparison to the corresponding TM 5 Si 3 and TMSi 2 , but also show better ductility compared to the corresponding TM-Si binary silicides. The nature of mechanical properties of TM 5 Si 3 C is revealed by the electronic structure and difference charge density. In addition, it is further found that four TM 5 Si 3 C have high melting points and excellent thermodynamic stability. Naturally, the better thermodynamic properties of TM5Si3C is related to the vibration of C atom in a system.