Abstract: Beta-Al₂O₃ structured ionic conductors, involving β- and β’’-Al₂O₃ phases, are among the most favorable solid electrolyte materials
for electrochemical sensors because of their excellent ionic conductivity and chemical stability. Usually they are used in tube or disc forms.
Microcrack-free beta-Al₂O₃ films on α-Al₂O₃ or its composite ceramic substrates were obtained by the surface reaction of the
substrate with lithium and sodium component from beta-Al₂O₃ atmosphere. SEM results show heterogeneous microstructures of the
beta-Al₂O₃ film, with some overgrown grains as large as 15μm. The addition of MgAl_2O_4 spinel phase in the α-Al₂O₃
substrate effectively improves the morphology of the films with maximum grain size of 2～3μm. The kinetic processes of the Na-beta-Al₂O₃
(Li,Mg) film formation on composite substrate are controlled by both the lithium transportation velocity and the rearrangement of α-Al₂O₃
to spinel structure of beta-Al₂O₃. Impedance analyses indicate that the beta-Al₂O₃ films obtained possess comparable electrical properties
to those of ceramic blocks and depend on the relative contents of β- and β’’-Al₂O₃, and obey the Arrehnius relationship.

Key words: beta-Al₂O₃, composite, ionic conduction