Terahertz dielectric response of nano-grained barium titanate ceramics measured by far-infrared spectroscopic ellipsometry

Abstract

The effect of grain size on ionic polarization of pure BaTiO3 ceramics was investigated. BaTiO3 ceramics with various grain sizes ranging from 434 nm to 1.85 μm were fabricated by a two-step sintering method. The samples indicated a similar trend in the relationship between grain size and permittivity at low frequencies as other studies, with 803 nm grains having the highest permittivity among the samples. In the THz region, the central, Slater, Last, and Axe modes were observed using a far-infrared ellipsometer. The vibration frequencies of the Slater, Last and Axe modes were 115, 179, and 490 cm−1, respectively, and did not change with decreasing grain size. In contrast, the central mode was shown to be influenced by the grain size. The grain size dependence of the central mode contribution was discussed based on the effect of the formation of 90° domain configurations and the grain boundary stress.