Dielectric response and polarization mechanism of alkali silicate glasses in gigahertz to terahertz frequency range

Abstract

AbstractOxide glasses are dielectric materials with potential applications in high‐frequency communications; hence, their dielectric properties in the gigahertz to terahertz frequency range should be investigated. In this study, the dielectric properties of silica glass and five single alkali silicate glasses were measured at 0.5–10 THz using terahertz time‐domain spectroscopy and far‐infrared spectroscopic ellipsometry. At 0.5–10 THz, the silica glass exhibited low dielectric dispersion with a low dielectric constant and loss. By contrast, the alkali silicate glasses exhibited high dielectric dispersion, and the dielectric constant and loss were higher than those of the silica glass. The shape of the dielectric dispersion profile depended on the alkali‐metal ions; it was broader for lighter ions such as Li ions and sharper for heavier ions such as Cs ions. The peak dielectric loss shifted toward a lower frequency as the weight of the alkali‐metal ions in the alkali‐silicate glass increased. To understand the dielectric dispersion, the complex permittivity was calculated using molecular dynamics simulations. The theoretical results qualitatively agreed with the experimental data. Ion dynamics analysis revealed that alkali‐metal ions vibrate and migrate under an applied electric field, which affects the dielectric constant and loss of alkali‐silicate glasses at gigahertz to terahertz frequencies. To fabricate filter devices at low temperatures, alkali metals should be added to silicate glass; therefore, a minimum amount of light alkali metals should be used to minimize the dielectric loss of the glass materials while maintaining productivity.