Electrical relaxation in mixed alkali iron pyrophosphate glasses

The electrical relaxation of mixed alkali, sodium and potassium, iron pyrophosphate 20[(1 - x)K2O-xNa(2)O]-20Fe(2)O(3)-60P(2)O(5), (0 less than or equal to x less than or equal to 1), glasses has been studied in the frequency range from 0.1 Hz to 10 kHz and over the temperature range from 303 to 423 K. The ac conductivity as a function of the temperature was divided into two domains, one where the absolute magnitude of ac conductivity is close to the de conductivity, and another when the absolute magnitude of ac conductivity is larger than the de conductivity. The thermally stimulated polarization current technique was used to study de conductivity in these iron phosphate glasses. The de conductivity calculated from thermally stimulated current measurements was in agreement with the de conductivity obtained from impedance measurements. At the same temperature, the de conductivity varies slightly in the glasses with different sodium and potassium content. The conductivity was examined on the basis that the activation energy for electronic conduction is lower than that for ionic conduction. The conductivity in these mixed alkali iron phosphate glasses depends upon iron oxide content which suggests electronic conduction. (C) 2000 Elsevier Science B.V. All rights reserved.