Phase transition, mechanical and electronic properties of Ti3B4 under high pressure

Abstract

We explore the crystalline structures for Ti3B4 in the 0–200 GPa pressure range via first-principles calculations based on density functional theory and advanced crystal structures prediction method using an evolutionary algorithm. The low-pressure-stable Immm phase of Ti3B4 gives way to a newly predicted orthorhombic phase (Pmmm) at 136 GPa. The B six-membered rings in the Immm phase transform to linked B zigzag chains in the Pmmm phase. Based on the electronic band structures, both Immm and Pmmm are metallic from 1 atm to 200 GPa; pressure-induced charge transfer promotes this phase transition. The simulated Vickers hardness values of Immm and Pmmm at ambient pressure are 41.5 and 34.9 GPa, respectively. The hardness of the Immm phase reduces with pressure while the opposite trend is observed for the Pmmm phase. These findings on the pressure-dependent properties of Ti3B4 yield insights into the intriguing high-pressure behaviors of the titanium-boron system.