Terahertz permittivity of rutile TiO<sub>2</sub> single crystal measured by anisotropic far-infrared ellipsometry

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  • KANEHARA Kazuki
    Nano-Phononics Lab., Graduate School of Science and Engineering, Tokyo Institute of Technology
  • HOSHINA Takuya
    Nano-Phononics Lab., Graduate School of Science and Engineering, Tokyo Institute of Technology
  • TAKEDA Hiroaki
    Nano-Phononics Lab., Graduate School of Science and Engineering, Tokyo Institute of Technology
  • TSURUMI Takaaki
    Nano-Phononics Lab., Graduate School of Science and Engineering, Tokyo Institute of Technology

Abstract

Rutile structured TiO2 has very high dielectric permittivities in non-ferroelectric materials. To understand the reason why rutile TiO2 has high ionic polarizabilities, it is essential to analyze accurate dielectric spectra of rutile TiO2 in the THz region. In this study, the complex permittivity of rutile TiO2 single crystal in the range 30–700 cm−1 (0.90–21 THz) was directly measured using the anisotropic far-infrared spectroscopic ellipsometer. The three Eu modes and one A2u mode, which are all infrared-active phonon modes in rutile TiO2, were observed. Moreover, the resonance frequencies of the phonon modes approximately were coincident with a calculation result of first-principles and the analysis data by a harmonic oscillator model. From the examination of the dielectric response, it was found that Eu(1) mode, which indicates the oscillation of Ti ions against O ions in the same phase, was dominant contributor to the static permittivity for a-axis. On the other hand, the high permittivity for c-axis was due to “soft” A2u mode.

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