关键词: transition metal boride, mechanical properties, density functional theory

Abstract: The phase stability, elastic anisotropy, and minimum thermal conductivity of MnB$_{2}$ in different crystal structures have been investigated by first-principles calculations based on density functional theory. The results found that $P$6$_{3}/mmc$ (hP6-MnB$_{2})$, $P6/mmm$ (hP3-MnB$_{2})$, Pmmn (oP6-MnB$_{2})$, $R\bar{{3}}m$(hR3-MnB$_{2})$, Pnma (oP12-MnB$_{2})$, and Immm (oI18-MnB$_{2})$ all exhibit mechanical and dynamic stability under environmental conditions, and the sequence of phase stability was hP6 > hR3 > oP6 > oI18 > oP12 >hP3. In addition, Vickers hardness calculations indicated that hP6, hR3, oP6, and oI18 of MnB$_{2}$ have potential as hard materials, while hP3 and oP12 are not suitable as hard materials. Moreover, the elastic anisotropy of different MnB$_{2 }$ phases were also comprehensively investigated. It is found that the anisotropic order of bulk modulus is oP12 > hP3 > hP6 > hR3 > oI18 > oP6, while that of Young's modulus is oP12 > hR3 > hP6 > oP6 > hP3 > oI18. Furthermore, the minimum thermal conductivity of different MnB$_{2}$ phases was evaluated by means of Clarke's and Cahill's models. The results suggested that these MnB$_{2}$ diborides are all not suitable as thermal barrier coating materials.

Key words: transition metal boride, mechanical properties, density functional theory