Crystal structures and mechanical properties of TaB5 and TaB6 from first-principles calculations

Utilizing the CALYPSO algorithm in conjunction with first-principles calculations, we theoretically explore the possible crystal structures of TaB and TaB. The calculated results show that the phase of TaB and 2 phase of TaB are the most thermodynamically favored structures among the predicted and substitute structures, and they can be synthesized at ambient pressure. The calculations of the phonon spectra and elastic constants demonstrate that the two predicted phases are dynamically and mechanically stable. The exceptional bulk modulus and significant hardness of these two materials verify that they are potentially ultra-incompressible and superhard materials. Additionally, the elastic anisotropy for the TaB and 2-TaB is also studied by applying sever good anisotropy indices and visual representations of the Young’s and bulk moduli in two and three dimensions. The in-depth analysis of the electronic structure and chemical bonding reveal that the robust covalent interactions of both B-B and B-Ta atoms within these phases mainly contribute to their stability and high hardness. These results will offer a theoretical foundation for the experimental synthesis of these two new materials.