Structural Phase Transitions, Electronic Properties, and Hardness of RuB₄ under High Pressure in Comparison with FeB₄ and OsB₄

Abstract

We have employed an evolutionary algorithm with first-principles calculations to investigate the pressure-induced structural evolution of RuB4 up to 500 GPa. The ambient phase is predicted to be a hexagonal structure (P63/mmc). The novel phases consisting of monoclinic (C2/c) and orthorhombic (Immm) structures are proposed to be the high-pressure phases at the pressure intervals of 198–388 GPa and beyond 388 GPa, respectively. The stability of the predicted phases is confirmed by both dynamic and elastic calculations. The electronic and mechanical properties of the predicted phases are evaluated and mainly discussed compared to the isoelectronic metal tetraborides, i.e., FeB4 and OsB4. In contrast to FeB4 and OsB4, all the stable phases of RuB4 are metal or semimetal, and any semiconducting phases do not emerge in the transformation pathway of RuB4. The nature of chemical bonding investigated by ELF, MPA, and pCOHP calculations reveals that the atomic configurations and the degree of covalent bonding of the predicted phases are responsible for lower hardness compared to those of FeB4 and OsB4. The results of this work provide more understanding of the family of metal tetraboride for designing metal-boride-based hard/superhard materials.

Lattice dynamic stability and electronic structures of ternary hydrides La1−xYxH3via first-principles cluster expansion

“…Note that for all our calculations regarding the La 1Àx Y x H 3 alloys, all the corresponding structures are evaluated without taking into consideration the entropy (S) contributions due to the fact that DFT works at 0 K and is capable of determining compounds closely resembling those found in experiment. [40][41][42][43][44][45][46] At this stage, it is worth mentioning once again that at the pressure of 20 GPa, La 0.8 Y 0.2 H 3 , La 0.75 Y 0.25 H 3 , and La 0.5 Y 0.5 H 3 have negative energies of formation relative to those of LaH 3 and YH 3 . Although formation energy suggests thermodynamic stability, it does not suffice to guarantee the existence of such compounds.…”

“…Note that for all our calculations regarding the La 1− x Y x H 3 alloys, all the corresponding structures are evaluated without taking into consideration the entropy ( S ) contributions due to the fact that DFT works at 0 K and is capable of determining compounds closely resembling those found in experiment. 40–46…”

High-temperature superconductor of sodalite-like clathrate hafnium hexahydride

“…Moving on to the pCOHP calculation, we described the character of the nature of a chemical bonding, which further supports the ELF calculation. This method can examine covalent bonding in several materials 11 , 49 , 50 . To further understand the superconductivity, the influence of bonding plays an important role in considering the value of .…”

Effect of substitution on the superconducting phase of transition metal dichalcogenide Nb(Se$$_{x}$$S$$_{1-x}$$)$$_{2}$$ van der Waals layered structure

“…5 b, pCOHP presents both bonding and anti-bonding. This implies that the distribution of electrons plays a significant role in the characteristics of the bonding 36 , 43 , 44 . Remarkably, it can be seen that Nb–S and the S–Se pairs interact via anti-bondings, while Nb–Se pair natural bonding.…”