Stabilization of New Phases in Ion-Conducting Nanocomposites

Physical properies of ion-conducting nanocomposites are reviewed. Special attention is paid to the change of the bulk characteristics of ionic salts in the nanocomposites due to the formation of the interface phases. The main thermodynamic reason of the formation of the nanocomposite as well as the stabilization of the interface phases is the adhesion energy _a. At sufficiently high _a values, the ionic salt tends to spread along the oxide surface, which leads to the formation of the nanocomposite on sintering. The adhesion is the result of the interface interaction and incorporates the stage of the specific adsorption of the interface ions. It leads to the formation of the double layer formed by the point defects in the interface region of the ionic salt. In the case of the strong adhesion, the structural reconstruction or the formation of the metastable interface phase takes place. Analysis of the experimental data shows that interface phases exist in composites AgI–Al₂O₃, MeNO₃–Al₂O₃ (Me = Li, Na, K, Rb, and Cs), CsHSO₄–SiO₂, RbNO₃–SiO₂ and CsCl–Al₂O₃. Their structure may be either epitaxial crystalline, or amorphous. The thickness of the interface phase as estimated on the basis of the brick-wall model is about 3–4 nm.