Prediction of Fe₂P-type TiTe₂ under pressure

Fe2P-type dioxides are significant both for geoscience and condensed-matter physics. For example, Fe2P-type SiO2 has been proposed to be one of the dominant components in the mantles of super-Earths and Fe2P-type TiO2 has been shown to have a large visible absorbance. Here we report the discovery of an Fe2P-type phase in a typical transition-metal dichalcogenide (TMD), TiTe2, using crystal structure prediction and first-principles calculations. Ambient layered TiTe2 will first transform to a monoclinic C2/m phase and then finally to the hexagonal Fe2P-type phase above 33 GPa. Fe2P-type TiTe2 is predicted to be metallic, contrasting with the semiconductivity of Fe2P-type TiO2. The same high-pressure phase (Fe2P type) appears both in transition-metal dioxides and TMDs, indicating that the stacking patterns of anions and cations play an increasingly important role in determining the high-pressure phase.