Unraveling Stable Vanadium Tetraboride and Triboride by First-Principles Computations

Transition metal polyborides (e.g., tetraborides or triborides) with intriguing boron configurations offer a unique combination of excellent mechanical, superconducting, optical, and thermoelectric properties. Unraveling the specific structures of polyborides is critical to understanding their underlying physical and electronic properties. Here, we perform first-principles calculations to focus on the predictions of geometrical structures, relative stabilities, and mechanical and electronic properties of vanadium tetraboride (VB4) and triboride (VB3). VB4 prefers to take Cmcm symmetry with a planar boron isosceles trapezoid, differing from earlier graphene-like or rhomboid boron arrangements in tetraborides. Upon compression, another new Amm2-type structure is energetically favorable above 12.0 GPa and can be stabilized up to 50 GPa. Both structures are qualified into incompressible and hard materials, comparable to previous reported tetraborides. Predicted C2/m-type VB3 possesses intriguing puckered boro...