Pseudo-dielectric functions, band-to-band transitions, and dielectric-related factors in a single-crystal LiTi2O4 thin film

This article is devoted to studying the optical properties of a novel single-crystal LiTi2O4 thin film. A high-quality (011)-oriented LiTi2O4 single-crystal thin film was prepared on a MgAl2O4 (011) substrate by pulsed laser deposition. The weak in-plane optical anisotropy is discovered by Mueller-matrix spectroscopic ellipsometry, which can be attributed to the cooperative Jahn-Teller distortion in the Ti–O octahedrons. The pseudo-dielectric functions were determined in the photon energy of 1.24–5.06 eV using the ellipsometric spectra. The optical conductivity, plasma frequency, effective mass, scattering time and other dielectric-related factors are also discussed. The critical points obtained in the pseudo-dielectric functions are originated from the charge-transfer transitions of the Ti related pairs. The results demonstrate that the enhanced effective mass is responsible for the high optical transparency of LiTi2O4 rather than the large high frequency dielectric constant ε∞.