Phase transitions and mechanical stability of TiO2 polymorphs under high pressure

Structures, phase transitions, elastic properties and mechanical stability of thirteen TiO2 polymorphs (fluorite, pyrite, rutile, anatase, hollandite, brookite, ramsdellite, columbite, cotunnite, modified fluorite, bronze, baddeleyite and hexagonal Fe2P-type phases) under pressure have been investigated using first-principles calculations. The optimal structural parameters and densities of thirteen TiO2 polymorphs under zero or high pressure have been obtained and analyzed. The pressures of phase transitions and stability-instability transitions have been predicted, particularly the latter has been systematically discussed using the modified Born stability conditions.