AC conductivity and impedance measurements in alkali boro-tellurite glasses

AC conductivity and impedance measurements were carried out for an alkali boro-tellurite glass system having composition 60B2O3-10TeO2-5TiO2-25R2O (where R — Li, Na and K). The impedance plots (Z″ (ω) vs. Z′ (ω)) for all glass samples were recorded and found to exhibit good single well-shaped semi circles over the studied temperature range. Frequency dependence of the imaginary part of impedance Z″(ω) and the imaginary part of modulus (M″) for all glass samples at different temperatures was also investigated. The conductivity isotherms show a transition from independent DC region to dispersive region where the conductivity continuously increases with increasing frequency. For low frequency region, conductivity values (σac) at RT are relatively low in the order of 10− 8 to 10− 9 (Ohm-cm)− 1. However, there is an increase in conductivity with temperature for all glass samples showing conductivities at 300 °C (σ300) in the range 10− 6 to 10− 5.5 (Ohm-cm)− 1. In the high frequency region, conductivity is enhanced by one order of magnitude (10− 5 (Ohm-cm)− 1) as temperature is increased. Power law parameter (s) is determined for all the glass samples at various temperatures and lowest ‘s’ values are found to be for lithium-containing glasses. An excellent time-temperature superposition in the imaginary part of the dielectric modulus (M″) confirms that the dynamical process is temperature independent and is also indicative of a common ion transport mechanism.