Electronic structure, bonding characteristics, and mechanical behaviors of a new family of Si-containing damage-tolerant MAB phases M5SiB2 (M = IVB—VIB transition metals)

Abstract

MAB phases are layered ternary compounds with alternative stacking of transition metal boride layers and group A element layers. Until now, most of the investigated MAB phases are concentrated on compounds with Al as the A element layers. In this work, the family of M5SiB2 (M = IVB—VIB transition metals) compounds with silicon as interlayers were investigated by density functional theory (DFT) methods as potential MAB phases for high-temperature applications. Starting from the known Mo5SiB2, the electronic structure, bonding characteristics, and mechanical behaviors were systematically investigated and discussed. Although the composition of M5SiB2 does not follow the general formula of experimentally reported (MB)2zAx(MB2)y (z = 1, 2; x = 1, 2; y = 0, 1, 2), their layered structure and anisotropic bonding characteristics are similar to other known MAB phases, which justifies their classification as new members of this material class. As a result of the higher bulk modulus and lower shear modulus, Mo5SiB2 has a Pugh’s ratio of 0.53, which is much lower than the common MAB phases. It was found that the stability and mechanical properties of M5SiB2 compounds depend on their valence electron concentrations (VECs), and an optimum VEC exists as the criteria for stability. The hypothesized Zr and Hf containing compounds, i.e., Zr5SiB2 and Hf5SiB2, which are more interesting in terms of high-temperature oxidation/ablation resistance, were found to be unfortunately unstable. To cope with this problem, a new stable solid solution (Zr0.6Mo0.4)5SiB2 was designed based on VEC tuning to demonstrate a promising approach for developing new MAB phases with desirable compositions.

Repelling effects of Mg on diffusion of He atoms towards surface in SiC: Irradiation and annealing experiments combined with first-principles calculations

“…The complete unification of experiments and calculations on the size-scale is challenged, but DFT is advantageous and acknowledged for the study of interatomic relationships at local locations in materials [54][55][56][57][58]. Simultaneously, the combination of experiments and calculations is one of the significant directions in materials research [58][59][60][61][62]. In this article, the doping of Mg at the Si site is demonstrated to be the lowest energy (Table 1 and Refs.…”

Improving the density functional theory prediction accuracy for elastic moduli and thermal expansion of MoAlB, Fe2AlB2, and Mn2AlB2

“…Recently, the ternary layered borides MAB phases, 1 as a result of inserting one/two Al layers into the binary borides, have attracted much attention because of their unique combination of ceramic and metal-like properties [2][3][4][5] in line with the well-established MAX phases. [6][7][8] In particular, their high fracture toughness, 9 high damage tolerance, 10 and oxidation resistance 11,12 indicate the great potential for high-temperature structural applications.…”

Lattice dynamics, Raman and IR vibrations of stable Al/Si‐containing MAB phases: An ab initio and experimental study

“…8 Various structural phases fall into this category, including 222 phases (Cmcm), [35][36][37] 212 phases (Cmmm), 38,39 314 phases (Pmmm), 34 and 416 phases (Cmmm). 34 Over time, the definition of the MAB phases is expanded to encompass additional phases such as 414 phases (Immm), where M layers are arranged adjacently, 15 as exemplified by Cr 4 AlB 4 , 40 and 512 phases (I4/mcm), [41][42][43] which both deviate from the general formula as mentioned above. Among these structures, the 222 phases feature nanolayers of transition-metal boride interleaved with an A-atoms bilayer, while the others only contain an A-atom monolayer.…”