AC conductivity and impedance measurements in alkali boro-tellurite glasses

Abstract

AC conductivity and impedance measurements were carried out for an alkali boro-tellurite glass system having composition 60B 2O 3-10TeO 2-5TiO 2-25R 2O (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 ( σ ac) 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 ( σ 300) 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.