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

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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 TM5Si3C Nowotny phase (NP) are studied by the first-principles calcualtions. Four TM5Si3C ternary phases (TM = Mo, Nb, W and Ta) are considered. It is found that the equilibrium structure of the Nowotny phase (NP) is a TM5Si3C. In particular, the Mo5Si3C, Nb5Si3C, W5Si3C and Ta5Si3C are firstly predicted. Nb5Si3C has better thermodynamic stability in comparison to the other TM5Si3C. Furthermore, the calculated elastic properties show that four TM5Si3C not only exhibit similar strength in comparison to the corresponding TM5Si3 and TMSi2, but also show better ductility compared to the corresponding TM-Si binary silicides. The nature of mechanical properties of TM5Si3C is revealed by the electronic structure and difference charge density. In addition, it is further found that four TM5Si3C 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.