Ab initio study of phase stability, elastic anisotropy, and minimum thermal conductivity of MnB 2 in different crystal structures

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 ( hP 6-MnB 2 ), P 6/ mmm ( hP 3-MnB 2 ), Pmmn ( oP 6-MnB 2 ), R 3 ¯ m ( hR 3-MnB 2 ), Pnma ( oP 12-MnB 2 ), and Immm ( oI 18-MnB 2 ) all exhibit mechanical and dynamic stability under environmental conditions, and the sequence of phase stability was hP 6 > hR 3 > oP 6 > oI 18 > oP 12 > hP 3. In addition, Vickers hardness calculations indicated that hP 6, hR 3, oP 6, and oI 18 of MnB 2 have potential as hard materials, while hP 3 and oP 12 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 oP 12 > hP 3 > hP 6 > hR 3 > oI 18 > oP 6, while that of Young’s modulus is oP 12 > hR 3 > hP 6 > oP 6 > hP 3 > oI 18. 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.