Dielectric polarizability of SiO₂ in niobiosilicate glasses

Abstract Understanding 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 (100‐2 x )SiO 2 ‐ x Nb 2 O 5 ‐ x Li 2 O 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 SiO 2 polarizability in niobiosilicates was calculated to be 6.16 Å 3 , which is much higher than the SiO 2 polarizability in fused silica glass (5.25 Å 3 ), alkali modified silicates (5.37 Å 3 ), and aluminosilicates (5.89 Å 3 ). The increasing trend in SiO 2 polarizability is attributed to the disruption in the connectivity of the SiO 4 tetrahedral network as it accommodates different network formers. The high SiO 2 polarizability of 6.16 Å 3 accurately predicts measured dielectric permittivity when Nb 2 O 5 = 25, 30, and 32.5 mol%, but overpredicts measured permittivity when Nb 2 O 5 ≤ 15 mol%, which is attributed to a decrease in SiO 2 polarizability as the percentage of corner sharing SiO 4 tetrahedra with NbO 6 octahedra goes down. This work demonstrates that SiO 2 polarizability depends on chemistry and connectivity of the glass, which has important implications in designing glass compositions for microwave frequency applications.