Li sites and phase stability in TiO2-anatase and Zr-doped TiO2-anatase

Abstract

The phase stability of Zr-doped Li-anatase has been studied for a wide range of Li concentrations using density functional theory calculations of representative ordered structures. Thermodynamically stable structures have been established through the full relaxation of the internal coordinates and the size and shape of the periodic unit cell. The stability of the Li-poor tetragonal phase is found to correspond to the Li occupancy in the centre of the octahedral sites. Occupancy of the off-centre site results in the formation of an orthorhombic phase, which is similar to that observed in Li-anatase. It is demonstrated that doping of anatase with Zr-ions does not affect the two-phase nature of Li insertion. Hypothetical high doping with Zr ions results in a decrease of the Li intercalation potential for anatase but within the solubility limit the effect is negligible. It is confirmed that Ti⁴⁺ ions play a major role in the accommodation of the electron density donated by Li and that the intercalation potential in the two-phase region is correlated to the participation of Ti ions in accommodation of the electron density.