First‐principles investigation of solution mechanism of C in TM‐Si‐C matrix as the potential high‐temperature ceramics

Although the TM‐Si‐C ternary compounds are promising advanced ceramics, the solution mechanism of C element in TM‐Si matrix is entirely unclear. In particular, the influence of C on the mechanical properties of TM‐Si matrix is no clear. To solve the problem, we apply the first‐principles calculations to study the occupied mechanism of C in TM 5 Si 3 silicides. In addition, the influence of C element on the mechanical properties of TM 5 Si 3 is further studied. Here, two typical TM 5 Si 3 phases: D8 l ‐Ta 5 Si 3 and D8 m ‐Mo 5 Si 3 are considered. For C‐doping, six C interstitial sites, Mo 5 Si 3 ‐C(1), Mo 5 Si 3 ‐C(2), Mo 5 Si 3 ‐C(3), Ta 5 Si 3 ‐C(1), Ta 5 Si 3 ‐C(2), and Ta 5 Si 3 ‐C(3), are designed. The calculated results show that six C‐doped TM 5 Si 3 matrices are thermodynamically stable. Among them, the C element prefers to occupy the Mo 5 Si 3 ‐C(2) and Ta 5 Si 3 ‐C(3) models. The calculated mechanical properties show that the additive C element weakens the bulk modulus, shear modulus, and Young's modulus of TM 5 Si 3 . However, the C element can improve the fracture toughness of Mo 5 Si 3 and Ta 5 Si 3 , which are in good agreement with the experimental phenomenon. Naturally, the improvement of fracture toughness is related to the formation of TM‐C bond and Si‐C bond.