Structural prediction of ultrahard semi-titanium boride (TiB) using the frozen-phonon method

The dynamical stability, crystal structure, and mechanical properties of semi-titanium boride (Ti 2 B) are extensively studied using the pseudopotential plane-wave method within first-principles calculations. Soft transverse acoustic phonon modes are identified in the material, which has been assumed for a long time to have an Al 2 Cu-type structure with a I 4/ mcm space group. Using the frozen-phonon method, a tetragonal I 4/ m structure is uncovered to be energetically more stable and have similar diffraction patterns compared to the previously assumed Al 2 Cu-type structure. Phonon dispersion and elastic constant calculations reveal the dynamical and mechanical stability of the I 4/ m structure of Ti 2 B at ambient pressure. The calculated high elastic constants, modulus, and ideal strength show that Ti 2 B possesses outstanding mechanical properties. Using the frozen-phonon method, a tetragonal I 4/ m structure with outstanding mechanical properties is uncovered to be energetically more stable than the previously assumed Al 2 Cu-type structure.