Dielectric polarizability of SiO2 in niobiosilicate glasses

Abstract

AbstractUnderstanding the mechanisms contributing to dielectric properties of glasses is critical for designing new compositions for microwave frequency applications. In this work, dielectric permittivity was measured using a cavity perturbation technique at 10 GHz for a series of niobiosilicate glasses with the compositions (100‐2x)SiO2‐ xNb2O5‐ xLi2O where x = 32.5, 30, 25, and 15 mol%. Permittivity measurements and glass compositions were used to calculate the polarizability of each cation‐anion unit in the glass network using the Clausius‐Mossotti equation. The SiO2 polarizability in niobiosilicates was calculated to be 6.16 Å3, which is much higher than the SiO2 polarizability in fused silica glass (5.25 Å3), alkali modified silicates (5.37 Å3), and aluminosilicates (5.89 Å3). The increasing trend in SiO2 polarizability is attributed to the disruption in the connectivity of the SiO4 tetrahedral network as it accommodates different network formers. The high SiO2 polarizability of 6.16 Å3 accurately predicts measured dielectric permittivity when Nb2O5 = 25, 30, and 32.5 mol%, but overpredicts measured permittivity when Nb2O5 ≤ 15 mol%, which is attributed to a decrease in SiO2 polarizability as the percentage of corner sharing SiO4 tetrahedra with NbO6 octahedra goes down. This work demonstrates that SiO2 polarizability depends on chemistry and connectivity of the glass, which has important implications in designing glass compositions for microwave frequency applications.