Phase separation and charge localization in UHV-lithiated anataseTiO2nanoparticles

Abstract

The insertion of lithium in anatase $\mathrm{Ti}{\mathrm{O}}_{2}$ nanoparticles under ultrahigh vacuum (UHV) conditions is studied using x-ray absorption spectroscopy (XAS) and resonant photoelectron spectroscopy (RPES) at the Ti ${L}_{2,3}$ edge. It is demonstrated that XAS can be used to monitor the separation into an anatase phase and a lithium titanate phase of formal stoichiometry ${\mathrm{Li}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{2}$. The initial state properties of the Ti $3d$ states of the lithium titanate phase are investigated using ab initio electronic structure calculations. The calculations show a correlation driven separation of Ti $3d$ states from the conduction band in agreement with previous studies. It is shown that Ti in different oxidation states (${\mathrm{Ti}}^{3+}$ and ${\mathrm{Ti}}^{4+}$) is formed as a direct consequence of the electron-electron interaction. RPES and XAS spectra confirm the presence of electronically inequivalent Ti sites. The site-sensitivity of the RPES spectra at selected electron binding energies is found to be consistent with the calculations.