Complex impedance analysis of silver-phosphate glassy system doped with different concentrations of silver iodide

Electric and dielectric properties of silver phosphate glass of the composition (NH4H2PO4)1−x (AgNO3)1−x(AgI)x (x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) were characterised using impedance spectroscopy. Samples were synthesized using the conventional melt quenching method. A decrease in the bulk resistance of the samples was observed with either increasing the temperature and/or dopant concentration, which indicates a semi-conducting behaviour with thermal activation conduction mechanism. In addition, the relaxation peak was observed to shift towards higher frequency with increasing temperature or dopant concentration. The slight asymmetrical shape of the relaxation peak together with the presence of the centre of the semicircle in Nyquist plot below the real axis indicate a non-Debye relaxation type. Electrical conductivity was found to switch from DC-conductivity to AC-conductivity at a certain frequency (crossover frequency). The crossover activation energy showed an inverse proportion with dopant concentration. The material was observed to follow Jonscher’s power law, where the values of the power law exponent were found to decrease with increasing temperature. This behaviour indicates that the dominant conduction mechanism can be well-explained in terms of the Correlated Barrier Hopping (CBH) model. The activation energy and the hopping energy were found to decrease with increasing AgI-dopant level, indicating an enhancement in the electrical conductivity of the samples.