Dielectric polarizability of alkali and alkaline-earth modified silicate glasses at microwave frequency

The dielectric properties of alkali and alkaline earth-modified silicate glasses were characterized in the frequency range where electronic and ionic polarizabilities contribute to permittivity. From the Clausius–Mossotti (CM) model, dielectric polarizability of each cation-oxygen constituent was determined from the permittivity and molar volume. The silicon–oxygen polarizability of silica glass (5.24 Å3) is significantly higher than that of crystalline quartz (4.87 Å3), suggesting that additional polarization modes contribute to glass permittivity. A full range of alkali species (Li, Na, K, Rb, and Cs) were then added as glass network modifiers through a series of binary silicate glasses, and the silicon–oxygen polarizability increased to 5.38 Å3. A similar trend was observed for alkaline-earth aluminosilicate glasses in which the polarizability increased with the addition of cationic modifiers to 5.89 Å3. CM analysis provides a method to explore the fundamental relationship between the glass structure and its unique polarization response in the microwave frequency range. Microwave permittivity values are predicted over broad compositional ranges for alkali and alkaline earth-modified silicate glasses using the CM relationship.