Using the first principles particle swarm optimization algorithm for crystal structural prediction, we have predicted a hexagonal P 6 _(3) / mmc structure of Tc _(2) C. The new phase is mechanically and dynamically stable, as verified by its elastic constants and phonon dispersion. The formation enthalpy–pressure curves show that the predicted P 6 _(3) / mmc -Tc _(2) C is more energetically favorable than the previously proposed Mo _(2) C-, anti -MoS _(2) -, Re _(2) P-, and Fe _(2) N-type structures in the considered pressure range. The calculated mechanical properties show that it is an ultra-incompressible and hard material. Meanwhile, the directional dependences of the Young's modulus, bulk modulus, and shear modulus for Tc _(2) C are systematically investigated. The analyses of the density of states and electronic localization function reveal the presence of strong covalent bonding between Tc and C atoms, which is of crucial importance in forming a hard material.
展开▼
