Terahertz dielectric response of single-domain BaTiO3 measured by far-infrared spectroscopic ellipsometry

The complex dielectric permittivity of single-domain BaTiO3 in the region of 30-700 cm(-1) (0.90-21 THz) was directly measured using a far-infrared spectroscopic ellipsometer. The dielectric responses of the Slater, Last, Axe, and O-4 torsional modes, which are all infrared-active phonon modes in BaTiO3 were clearly observed. The resonance frequencies of the phonon modes estimated in this study were in agreement with the previous data estimated by analysis of reflection spectra using a harmonic oscillator model. These results indicate that the far-infrared ellipsometric technique is effective for analyzing the phonon modes of BaTiO3 single crystals. Additionally, we examine the dielectric response and the damping of the soft mode with respect to the order-disorder model. (C) 2014 The Japan-Society of Applied Physics