Effects of mixed-alkali oxides on AC conductivity and dielectric properties of xNa2O-(20-x)K2O-30V2O5-50TeO2 glasses

The melt-quenching technique was used to prepare tellurovanadate glasses containing sodium and potassium oxides with compositions of xNa(2)O-(20-x)K2O-30V(2)O(5)-50TeO(2) (x = 0-20 mol%) to examine the impact of mixed-alkali oxide on alternating-current (AC) conductivity and dielectric properties. Structural analysis revealed the presence of bridging oxygen (BO) and non-bridging oxygen (NBO). Thermal analysis results demonstrated a minimum value of glass transition temperature (T-g) at x = 10 mol% with an increase in Na2O content. The variation of AC conductivity (sigma(ac)) revealed a non-linear behaviour with Na2O at temperature < 383 K, where sigma(ac) increased to maximum value at x = 15 mol% and shifted to x = 10 mol% at temperature >= 383 K. This result may be attributed to mixed-alkali effect (MAE) because of the mixing of the two alkali oxides. The increase in sigma(ac) with Na2O might be due to increase in the carrier pathway caused by the opening up of the glass network as NBO increased. Meanwhile, dielectric constant (epsilon') demonstrated an optimal increase at x = 10 mol% prior to the reduction greater than x = 10 mol%. The maximum epsilon' value at x = 10 mol % was in accordance with the sigma(ac) anomaly, which may also related to the MAE that induced formation of heavy dipoles. Consequently, this facilitated the dipole orientation in the glass network. Conduction mechanism at the dispersion region for all glass samples was found to be the correlated barrier hopping (CBH) model. The electrical modulus of the investigated samples revealed the non-Debye type relaxation, which indicates presence of interaction between ions.