Acta Physica Sinica, Volume. 69, Issue 11, 116201-1(2020)
Transition-metal light-element compounds are potential candidates for hard materials. In the past, most of studies focused on the binary transition metal borides, carbides and nitrides, while the researches of ternary phases are relatively rare. In this paper, the structure units of the known Nb3B3C and Nb4B3C2 phases are first analyzed to be Nb6C octahedron and Nb6B triangular prism, respectively. By stacking the Nb6C octahedron and Nb6B triangular prism, twenty ternary Nb-B-C and twenty ternary Ta-B-C configurations with different compositions are constructed. The chemical formula of these Nb-B-C and Ta-B-C configurations can be defined to be Nb(m + n + 2)B(2m + 2)Cn and Ta(m + n + 2)B(2m + 2)Cn, respectively. Using first-principles density functional calculations, thermodynamical, dynamical and mechanical stabilities of the constructed ternary Nb-B-C and Ta-B-C configurations are investigated through calculating their enthalpies of formation, phonon dispersions and elastic constants. Five Nb-B-C (Nb3B3C, Nb4B3C2, Nb6B4C3, Nb7B4C4 and Nb7B6C3) phases and six Ta-B-C (Ta3B3C, Ta4B3C2, Ta6B4C3, Ta7B4C4, Ta7B6C3 and Ta3BC2) phases are predicted to be stable by analyzing the constructed ternary Nb-B-C and Ta-B-C phase diagrams, in which the seven phases (Nb6B4C3, Ta3B3C, Ta4B3C2, Ta6B4C3, Ta7B4C4, Ta7B6C3 and Ta3BC2) are first predicted to be stable. The Nb6B4C3, Ta6B4C3, Ta4B3C2 and Ta3B3C phases are stable when temperature is higher than 1730, 210, 360 and 1100 K, respectively. And the Ta3BC2 phase is stable only when temperature is lower than 130 K. The calculated results about mechanical and electric properties show that these Nb-B-C and Ta-B-C phases are conductive materials with a high hardness in a range of 23.8–27.4 GPa.
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Qian-Ku Hu, Shuang-Hong Qin, Qing-Hua Wu, Dan-Dan Li, Bin Zhang, Wen-Feng Yuan, Li-Bo Wang, Ai-Guo Zhou.
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Received: Feb. 18, 2020
Accepted: --
Published Online: Dec. 2, 2020
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