Migration of sodium and lithium interstitials in anatase TiO^sub 2

Titanium oxide and in particular anatase is an important material due to its high chemical stability and photocatalytic properties, with the drawback that its large band gap constrains its photocatalytic activity to only a small portion of the solar spectrum. Recently, titanium oxide has been doped with lithium and sodium to consider its potential application in Li-ion and Na-ion batteries, respectively. In the present investigation, we employ density functional theory to study the structure, electronic properties and migration of lithium and sodium interstitials in anatase as these can be important for battery applications. It is shown that the introduction of lithium and sodium interstitials results in energy levels into the band gap. The migration energy barriers of lithium and sodium interstitials are 0.32 eV and 0.56 eV respectively.