Effects of mixed glass former on AC conductivity and dielectric properties of 70[xTeO2+(1-x)B2O3]+15Na2O+15K2O glass system

Abstract

Mixed glass former of composition 70[xTeO2+(1-x)B2O3]+15Na2O+15K2O where x = 0–0.7 mol% have been prepared by melt quenching method to investigate their structural, AC conductivity, and dielectric properties. The variation of conductivity (σ′) with TeO2 showed a non-linear behaviour, where decrease to a minimum value at x = 0.4 mol% before increasing for x > 0.4 mol%. The minimum is suggested to be due to the low migration of Na+ and K+ ions caused by the mixed glass former effect (MGFE). Meanwhile, dielectric constant (ε′) showed a slight increase for x ≤ 0.4 mol% followed by a large increase for x ≥ 0.5 mol% TeO2. The large increase in dielectric constant (ε′) for x ≥ 0.5 mol% is suggested to be due to the presence of some crystalline phase within the amorphous matrix. Structural analysis of the present glass system reveals N4 reached minima at x = 0.2 mol% and 0.4 mol% with addition of TeO2 which attributed to the structural changes due to the conversion of BO4 to BO3 units. Glass transition temperature, Tg exhibited a non-linear increase for x ≤ 0.5 mol% followed by a large increase at x > 0.5 mol%. The conduction mechanism at low frequency region was found to be Inverse – Overlapping Large Polaron Tunnelling (Inverse – OLPT) for x ≤ 0.5 mol%, while the mechanism transformed to the OLPT model for x = 0.7 mol%. The electric modulus of the present glass system showed an asymmetric peak of M’, that reflected a non-Debye type relaxation.