Orthorhombic distortion on Li intercalation in anatase

The mechanism of the tetragonal-to-orthorhombic transformation upon Li-intercalation into anatase structured titania has been studied using first principle calculations. The primary mechanism for the formation of the orthorhombic phase is found to be the accommodation of donated charge in localized Ti-d(yz) orbitals leading to a cooperative Jahn-Teller-like distortion of the lattice. This model is examined further by considering electron addition states in pure anatase and the analogous structures of H0.5TiO2 and Na0.5TiO2. It is shown that the rigid band model is not valid and population of the degenerate Ti-d(xy,yz) orbitals occurs beyond a critical concentration due to the repulsive interaction of the localized electrons. It is shown that the stability of the Li0.5TiO2 structure is related to the similarity of the ionic radius of Li+ and Ti+3 ions. Optimal configurations of H0.5TiO2 and Na0.5TiO2 are also predicted.