Ab initio study of temperature- and laser-induced phase transitions in TiO2

Abstract

We analyze the bulk phase transitions of the three titanium dioxide polymorphs anatase, rutile, and brookite in thermodynamical equilibrium and after ultrafast laser excitation using the generalized solid-state nudged elastic band (G-SSNEB) method. For calculating the forces and stresses needed for G-SSNEB, we use electronic-temperature dependent density functional theory calculations. Our results show that the anatase-rutile and brookite-rutile phase transitions have a considerably lower energy barrier than the anatase-brookite phase transition in the thermodynamical equilibrium and upon laser excitation. The obtained transition temperatures in thermodynamical equilibrium are consistent with experimentally observed ones. Furthermore, our calculations show that the pathways of the phase transition are not affected considerably by the applied laser pulse. Although the pathways do not change considerably we see that the rutile phase is stabilized by the laser pulse.