Structural, mechanical properties and fracture mechanism of RuB(1.1).

Polycrystalline RuB(1.1) has been prepared by using an arc-melting method and its structure and mechanical properties including elastic modulus, hardness and fracture behavior have been characterized. Also, the electronic structure and bond characteristics for this compound have been investigated by first-principles calculations. The lattice parameters of RuB(1.1) have been precisely determined by a Rietveld refinement. First-principles calculations show that this compound has a high bulk modulus and a big Poisson's ratio compared to RuB2. The measured hardness of ~10.6 GPa for RuB(1.1) is three times lower than the theoretical value. This low hardness can be attributed to bond characteristics such as the bonding state and orientation, and fracture mechanism, in which the features of the Ru-B bonds plays an important role in the hardness. We found that there is an isosceles triangle bonding state including the B-B and Ru-B bonds, and the two-dimensionally inclined Ru-B bonds along the a-b plane weaken the hardness and C33. The scanning electron microscopy images show that this RuB(1.1) compound exhibits a twinning fracture, and this fracture model is also confirmed by first-principle calculations.