Structural and relative stabilities, electronic properties and possible reactive routing of osmium and ruthenium borides from first-principles calculations

Abstract

First-principles calculations are employed to provide a fundamental understanding of the structural features and relative stability, mechanical and electronic properties and possible reactive route for osmium and ruthenium borides. The structural searches and calculations of the formation enthalpy identify a low-energy monoclinic phase for OsB3 with P2(1)/m symmetry, an orthorhombic phase for OsB4 with Pmmn symmetry, an orthorhombic phase for RuB3 with Pnma symmetry and a hexagonal phase for RuB4 with P63/mmc symmetry. Also, the structure transition at high pressure is also predicted for MB3 and MB4 (M = Os and Ru). Moreover, among the borides, orthorhombic RuB3 and OsB4 phases are predicted to be potential hard materials with estimated Vickers hardness values of 26.3 and 31.3 GPa, respectively. The analysis on the electronic properties and crystal orbital Hamilton population shows that the directional boron-boron networks, together with the strong metal-boron bonds, are responsible for their excellent mechanical properties. Relative enthalpy calculations with respect to possible constituents are also investigated to assess the prospects for phase formation and an attempt at high-pressure synthesis is suggested to obtain osmium and ruthenium tri- and tetra-borides.

Evolution of boron clusters in iron tetraborides under high pressure: semiconducting and ferromagnetic superhard materials

“…Several known polymorphous metal tetraborides from previous studies were reexamined in the FeB 4 system, including orthorhombic oP10-FeB 4 (no. 194, P6 3 /mmc, Z ¼ 2), 27 which are denoted hereinaer as 58-, hp20-, 71-, 59-, 194-FeB 4 , respectively. 194, P6 3 /mmc, Z ¼ 4), 24 orthorhombic oI10-CrB 4 type (no.…”

A New Superhard Phase and Physical Properties of ZrB3 from First-Principles Calculations

“…Further, Poisson’s ratio v is a crucial parameter to describe the degree of directionality for the covalent bonding. From Table 1, the v value of the C 2/ m -ZrB 3 (0.14) is a little larger than that of ZrB 2 [42], the same as ZrB 4 [27], and much smaller than those of the other TM borides mentioned above [45,46,47,48], which means there is a strong degree of covalent bonding due to the presence of the planar six-membered ring boron network. To describe the brittleness or ductility of materials, Pugh [49] proposed an experimental criterion by the ratio G / B .…”

“…The calculated bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio of the C 2/ m phase together with the reference materials mentioned above are listed in Table 1. As seen from Table 1, the predicted C 2/ m phase has a larger bulk modulus of 238 GPa, which is larger than those of ZrB [17,18,19,28,41] and ZrB 12 [26,28,43] but comparable to those of ZrB 2 [17,20,21,28,42], ZrB 4 [27], and other TMB 3 (TM = Mo, W, Ru, Os) [45,46,47,48]. This indicates that the C 2/ m phase is difficult to compress.…”

First-principles calculation of structural, thermodynamic and mechanical properties of 5d transitional metal triborides TMB3 (TM=Hf–Au)

“…TcP 3 structure (Fig. 1f) has three nonequivalent Wyckoff positions for B atoms, i.e., 4e (0.0, 0.25, À0.0308), 4e (0.0, 0.25, 0.2189) and 4e (0.0, 0.25, À0.1541), respectively, while Ta occupies the 4e (0.0, 0.25, 0.4022) sites [28,29].…”

“…Half of the B atoms are sevenfold coordinated with four B and three TM atoms, while the other half of the B atoms are located at the center of a trigonal bipyramid formed by six TM atoms and coordinated by two B atoms. Each TM atom is coordinated by eight B atoms and locates at [27,28]. For WB 3 structure (Fig.…”