The investigation of hardness and bonding behavior in XB4 , X = {Ce, Th, U, Pa}, tetraborides by first-principles

The mechanical and electronic properties of XB4, X = {Ce, Th, U, Pa}, tetraborides have been studied by using first-principles based on density functional theory. The results show that these boron-rich solids are mechanically and thermodynamically stable. From the calculated band structure and density of states, we obtained that they have metallic character. When the calculated parameters related to the crystal structure were considered with the bonding characteristics, the microscopic hardnesses of these boron-rich solids can be theoretically calculated. The obtained hardness values indicate that, these materials are hard, but not superhard. Furthermore, from the detailed hardness analysis, we found that the octahedron structural unit of the structure has an important role on the total hardness of the materials.