The stability, elasticity and hardness of Ru2B and RuB: A first-principles study

Abstract

We have used particle swarm optimization algorithms to perform an efficient search for the structures of Ru2B and RuB in the pressure range 0–100 GPa. The results show that the hexagonal P-6m2 structure of Ru2B is energetically most favorable at atmospheric pressure and that a more stable c2/m structure emerges at 29.3 GPa as the pressure increases. For RuB, we find a new hexagonal P-6m2 structure that is more stable than the previously proposed WB-type structure. The hexagonal P-6m2 structure is energetically most favorable throughout the pressure range, with the tightly packed Ru and B layers in RuB alternately stacked to form a mesh structure. As the boron content increases, the formation of strong covalent bonds between the Ru and B atoms enhances the hardness of the compound, and RuB is an incompressible material with a hardness of 20.44 GPa.