Behavior of the low-frequency conductivity of silver iodide nanocomposites in the superionic phase transition region

Abstract

The behavior of the specific conductivity of composites based on silver iodide embedded in porous glasses with an average pore diameter of 7 ± 1 nm and in artificial opals with a pore diameter of 40–100 nm has been investigated in the temperature range from 300 to 500 K. It has been shown that a decrease in the characteristic pore size does not lead to a change in the order of the phase transition and that the temperature of the transition to the superionic state of silver iodide in a porous glass and in an opal upon heating is close to the phase transition temperature Tc in the bulk material (∼420 K). Upon cooling, the phase transition temperature Tc significantly decreases, and the phase transition becomes diffuse. With a decrease in the pore size, the region of the temperature hysteresis of the phase transition increases. The dc conductivities of the composites have been estimated from the impedance diagrams. The temperature dependence of the dc conductivity of both composites has a thermally activated nature, and the slope of the curve σ(1/T) changes near the phase transition, which indicates a change in the activation energy. The activation energies in the low-temperature and high-temperature phases have been estimated at ∼450–470 and ∼100 meV, respectively. The equivalent electrical circuit describing the charge transfer processes in the studied samples has been proposed.