HIGH IONIC-CONDUCTIVITY AND UNUSUAL THERMODYNAMIC PROPERTIES OF SILVER-IODIDE IN AGI-AL2O3 NANOCOMPOSITES

Composites (1-x)AgI-xAl(2)O(3) were obtained using mechanical treatmen t of pure AgI with highly dispersed alumina (specific area 270 m(2)/g) in planetary ball mill followed by sintering at 570-870 K. As the con centration of alumina rises, properties of the composites change: both temperature of the superionic phase transition and the heat of the tr ansformation decreases. Average grain size of AgI diminishes with x an d at x > 0.6 becomes less than 100 nm, hence, the composites may be at tributed to nanocomposites. The phase transition, being very sharp in AgI, becomes diffusive for x > 0.5, the absolute values of the conduct ivity of both phases approaches each other. All the facts mentioned ma y be explained by strong interface interaction between Al2O3 and AgI i n the nanocomposites leading to a stabilization of a metastable high-d isordered state of AgI at low temperatures. Properties of the composit es are shown to be sensitive to agents adsorbed on the alumina surface . Silver iodide occurring in a metastable state within the composite m ay be easily transformed to stable beta-AgI by treatment with water va pour. It is likely that water molecules substitute for Ag+ ions weakly bonded to surface oxygen atoms of alumina, destroying the AgI-Al2O3 i nterfaces.