High-Pressure Phase Diagram of the Ti-O System.

Titanium oxides are technologically important compounds. The chemistry of the Ti-O system is quite rich, largely because of the multiple oxidation states that titanium atoms can take. In this work, using a combination of variable-composition evolutionary crystal structure prediction (USPEX code) and data mining (Materials Project), we predicted all of the stable titanium oxides in the pressure range 0-200 GPa and found that 27 compounds can be stable at different pressures. We resolved contradictions between previous works and predicted four hitherto-unknown stable phases: P21/c-TiO3, I4/mmm-Ti3O2, Imm2-Ti5O2, and R3̅-Ti12O5. We also showed that the high-pressure P6̅m2-TiO phase is an electride.