Ten-fold coordinated polymorph and metallization of TiO2 under high pressure†
Titanium dioxide (TiO2) has a wide range of industrial applications (e.g., in photocatalysis and solar cells). Pressure causes profound structural and electronic changes in TiO2, leading to the fundamental modification of its physical properties. We report the metallization of TiO2 at high pressures through first-principles swarm structure searching calculations. Metallization accompanies the stabilization of a body-centered tetragonal CaC2-type structure (space group I4/mmm), which is more stable than the Fe2P-type structure above 690 GPa. This phase adopts a ten-fold coordinated structure consisting of face-sharing TiO10 dodecahedrons, the highest coordination number among all TiO2 phases known so far. In contrast to the nine-fold Fe2P-type structure, the higher coordination and denser polyhedral packing makes the CaC2-type structure energetically favorable. Our work enables an opportunity to understand the structure and electronic properties of TiO2 at high pressures.