Ionic conduction in silver phosphate glasses doped with silver sulphide

The dielectric properties of (Ag2S)(x)(AgPO3)(1-x) and AgPO3 ionic glasses have been investigated at low frequencies (10 Hz - 10 MHz) by complex impedance measurements in the temperature range between 20 and 330 K and at microwave frequencies (8.2-18 GHz) using a waveguide transmission line and also a cavity resonator at 9 GHz from 77 to 300 K. Analysis on the basis of the jump relaxation model has shown that translational and reorientational hopping motions of mobile Ag+ ions are responsible for the observed frequency-dependent ac conductivity. The temperature dependence of the ac conductivity at fixed frequencies can be fitted using three relaxation processes with characteristic activation energies which differ from each other by an order of magnitude and are closely similar to those obtained from previous ultrasonic attenuation studies on the same glasses. The highest energy (about 0.4 eV) has been associated with the translational hopping motion, responsible for the long-range ionic diffusion through the glasses in the low-frequency limit. The smallest activation energy (about 10 meV) has been ascribed to the topological disorder characteristic of glassy materials and probably corresponds to ion hopping between nearly energetically equivalent available sites. The intermediate energy values (0.05 - 0.1 eV), which depend on the concentration of the modifier, are likely to characterize different reorientational motion and/or different jump lengths.