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.