First-principles investigation of TiB3 under high pressure

The structural stabilities of TiB3 under high pressure have been studied by using first-principle calculations. Results show that TiB3 transforms from the C2/m phase to P2/m phase at 74.7 GPa. The C2/m-TiB3 and the high-pressure P2/m-TiB3 are all hard materials, with hardnesses of 46.7 GPa and 45 GPa calculated at atmospheric pressure, respectively. As can be seen, the negative formation enthalpies suggest that they are stable and could be synthesised at atmospheric pressure. The ELF calculations reveal that there are very strong covalent bonds be-tween the boron atoms in both phases, and this is an important reason for the high hardness. Moreover, the mechanical properties of TiB3 in the two phases are discussed.