Analysis of dielectric response of TiO2 in terahertz frequency region by general harmonic oscillator model

The terahertz range dielectric response of polycrystalline TiO2 (rutile) ceramics and rutile single crystals were invetigated by analyzing infrared-active e phonons by both Fourier-transform far-infared (FT-FIR) reflectivity measurement and terahertz time-domain spectroscopy (THz-TDS). The dielectric functions at room temperature measured by THz-TDS are well expressed using the general harmonic oscillator model. We found that the imaginary part of the dielecrict permittivity of the TiO2 ceramic is threefold higher than that of the rutile single crystal at 300K. The large dielectric loss is attributed to the additional damping of the A(2u) mode or/and an increase in the phonon damping. The low-temperature dielectric loss of the rutile single crystals is exceedingly low. However, TiO2 ceramics shows little temperature dependence. These results indicate that extrinsic scatterng significantly affects the dielectric loss oof the TiO2 ceramics in the THz region.