Investigation of the optical properties of LiTi₂O₄ and Li₄Ti₅O₁₂ spinel films by spectroscopic ellipsometry

The spinel lithium titanates materials Li₄Ti₅O₁₂ and LiTi₂O₄ were fabricated by pulsed laser deposition. High quality and single phase thin films were successfully grown, thus opening the door for a systematic investigation of the optical properties of the spinel system Li_1+xTi_2-xO₄ (0≤ x ≤1/3). The microstructure of Li_1+xTi_2-xO₄ films were characterized by X-ray diffraction and atomic force microscope. The optical properties of the films were studied by spectroscopic ellipsometry at room temperature. The refractive index, extinction coefficient, and the thickness of the films were obtained by fitting the experimental data over the entire measured wavelength range. The results show that the two spinel oxides exhibit absolutely different dispersion trends in the visible region. The optical band gap of Li₄Ti₅O₁₂ is about 3.14eV. The crystal-field energy splitting of LiTi₂O₄ is about 2.09eV between the eg and the t2g orbitals.