ZrB2: Adjusting the phase structure to improve the brittle fracture and electronic properties

Although ZrB2 is a promising ultrahigh-temperature ceramic, the intrinsic brittleness and low fracture toughness are the main bottlenecks. To solve these key problems, by means of first-principles calculations, we predict ZrB2 new phases, and investigate the influence of new phase on the mechanical properties and electronic properties of ZrB2. The calculated results show that two new ZrB2 phases: RuB2-type with orthorhombic structure (Pmmn, No.59) and ReB2-type with hexagonal structure (P63/mmc, No.194) are dynamical stability at the ground state. Although RuB2-type and ReB2-type structures weaken the volume deformation resistance and shear deformation resistance of ZrB2, it results in brittle-to-ductile transition due to the formation of weak Zr-B bond along the shear direction. Importantly, ReB2-type structure improves the electronic properties of ZrB2 because of the strong charge overlap between conduction band and the valence band near Fermi level (E-F). Therefore, our work can open up a new clue to improve the ductility and electronic properties of ZrB2.