New stable transition metal carbonitrides: TM3C2N, TM3CN2, and TM4C3N

Transition metal carbonitrides have been widely applied in various fields due to their excellent physical and chemical properties. In the pursuit of identifying innovative and stable crystal structures among transition metal carbonitrides, we have employed first-principles calculations to investigate the substitution of transition metal elements (Cr, Hf, Mo, Nb, Ti, V, W, Zr) for Ta within three stable crystal structure types: Ta₃C₂N, Ta₃CN₂, and Ta₄C₃N. The thermal stability, dynamic stability, and mechanical stability of these twenty-four structures were systematically studied, and nine stable new crystal structures were finally identified. Our subsequent investigations have included assessments of their structural, electrical, and mechanical properties. Our findings in mechanical properties have revealed that five compounds, Nb₃CN₂, Hf₄C₃N, Nb₄C₃N, Ti₄C₃N, and Zr₄C₃N, exhibit hardness values of 20.3 GPa, 30.0 GPa, 22.4 GPa, 28.7 GPa, and 26.2 GPa, respectively. Furthermore, our electronic property assessments have indicated that these structures exhibit metallic characteristics.