Pressure-induced phase transition of TaOx compounds from first-principles investigations

Using particle-swarm optimization algorithm and first-principles calculations, we have systematically investigated the phase stability of Ta–O compounds (TaO_x, x = 1, 1.5, 2, 2.5, and 3) at pressures up to 200 GPa. We successfully discover new structures of TaO_x that exhibit outstanding dynamical, thermodynamic, and mechanical stability at elevated pressures. Especially, at ambient pressure, TaO, Ta₂O₃, TaO₂, Ta₂O₅, and TaO₃ adopt $Pm\bar{3}m$, Pbcn, P4₂/mnm, Pbam and $Pm\bar{3}m$ phases, which transform to P4/nmm (146 GPa), Pnma (39 GPa), P2₁/c (34 GPa), C2/c (8 GPa) and $Im\bar{3}$ (124 GPa) phases respectively, highlighting the important role of pressure in driving structural phase transition. Analyses on chemical bonding characteristics suggest the ion nature of these structures, and electronic structure calculations demonstrate that P4/nmm TaO, Pnma Ta₂O₃, P2₁/c TaO₂, and $Im\bar{3}$ TaO₃ exhibit metallic behaviors, while C2/c Ta₂O₅ is an insulator with a sizable band gap of 4.2 eV. We expect these results to provide valuable insights into the structural and electronic properties of TaO_x at high pressures, which may open up new possibilities for exploring the potential applications of technologically important oxides in harsh conditions.