Terahertz dielectric response of single-domain BaTiO₃measured by far-infrared spectroscopic ellipsometry

Abstract

The complex dielectric permittivity of single-domain BaTiO 3 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 BaTiO 3 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 BaTiO 3 single crystals. Additionally, we examine the dielectric response and the damping of the soft mode with respect to the order-disorder model.

Effect of oxygen vacancies on intrinsic dielectric permittivity of strontium titanate ceramics

“…The measurement principles and the details of the ellipsometer are described in previous reports. 33),34),38) Ionic polarizations originating from three kinds of optical phonon modes, i.e., the Slater, Last, and Axe modes, were measured directly to discuss the effect of oxygen vacancies in strontium titanate ceramics.…”

“…However, the Slater-type soft mode of BaTiO 3 is known to be the overdamped phonon mode, which is difficult to be observed directly using conventional methods. 33) For this reason, no direct evidence for hardening of the soft mode has not been reported yet. In contrast, the intrinsic permittivity of strontium titanate (SrTiO 3 ) can mainly be explained by ionic polarization alone, and the Slater-type soft mode of SrTiO 3 is the underdamped mode, 34)36) suggesting that hardening of the soft mode caused by oxygen vacancies may be directly observed in a THz dielectric spectrum.…”

Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics

“…The maximum observable frequency of THz-TDS is a few THz, and it is difficult to observe all TO modes. Another new technique for a broadband THz study is far-infrared spectroscopic ellipsometry, where the maximum frequency is about 20 THz [14].…”

Terahertz permittivity of rutile TiO₂ single crystal measured by anisotropic far-infrared ellipsometry

“…13), 14) In this study, we measured the complex permittivity of rutile TiO 2 single crystal at 0.921 THz using the anisotropic farinfrared ellipsometric system for understanding excellent dielectric properties of rutile TiO 2 from the phononic view point.…”