Mechanism of THz dielectric constant enhancement in multi-component oxide glasses investigated by infrared and THz spectroscopies

Dielectric properties of multi-component silicate oxide glasses are investigated with a focus on high dielectric constant oxyfluorosilicate (OFS) glasses by using the infrared reflection spectroscopy and terahertz (THz) time-domain spectroscopy. On the basis of multiple Lorentz oscillator model, vibrational parameters and most responsible ionic pairs are identified for major modes in OFS glasses. The lowest frequency mode is found to dominate the total THz dielectric strength. Among various glasses, the high frequency (optical) dielectric constant shows a superlinear dependence on the electronic polarizability of oxygens. In contrast, the low frequency (THz) mode contribution to the dielectric constant is enhanced by the ionicity (expressed by the polarization ionicity parameter) and exhibits an even steeper dependence on the electronic polarizability. This feature well explains the mechanism of attaining the highest THz dielectric constant in an OFS glass (e.g. ZNbKLSNd glass). Also, the oxygen ion effective charges bearing the lowest frequency modes of OFS glasses are evaluated and found to behave consistently with the polarization ionicity parameter, confirming the relevance of both of these parameters as good ionicity indicators.