Percolation effect, thermodynamic properties of AgI and interface phases in AgI-Al2O3 composites

Properties of AgI in (1-x)AgI-xAl(2)O(3) composites were studied by X-ray powder diffraction, electrophysical and electrochemical methods, infrared spectroscopy and differential scanning calorimetry. Frequency dependencies of conductivity and dielectric permittivity were analyzed. Two maxima were found on concentration dependence of the dielectric permittivity at x = 0.2 and 0.9 in agreement with the two-threshold percolation model. As it was shown from studies of electrochemical cells, Gibbs free energy of AgI in the composites exceeds the corresponding values for pure AgI. Analysis of calorimetric data indicates the presence of three AgI phases in the composites - two crystalline ones with different temperatures of alpha-beta transition and an amorphous phase. Their concentration was estimated from calorimetric data. The thickness of the interface amorphous AgI layer was estimated by means of a simple brick-wall model as 3+/-1 nm. (C) 2000 Elsevier Science B.V. All rights reserved.