Trivalent Al3+ ion conduction in aluminum tungstate solid

Ionic conduction of trivalent aluminum in solid aluminum tungstate, Al-2(WO4)(3), has been directly and quantitatively demonstrated. Trivalent ions especially for aluminum where the polarizability is considerably low, are strongly bonded in a crystal lattice and have been believed to be unlikely to exhibit migration in solids because of high electrostatic interaction with the surrounding skeleton structure. The material, Al-2(WO4)(3), which has the Sc-2(WO4)(3) structure, was selected in order to reduce the interaction between the framework and the mobile species, Al3+, as much as possible. The ionic conduction characteristics of Al-2(WO4)(3) were investigated by means of electrolysis and electromotive force measurement by constructing an aluminum concentration cell. The typical electrical conductivity of Al-2(WO4)(3) was, approximately 2 x 10(-5) S cm(-1) at 800 degrees C. The dc electrolysis data strongly support the conclusion that ionic Al3+ is the mobile species in Al-2(WO4)(3). By further electrochemical measurements, it was confirmed that the mobile species was aluminum ion in a trivalent state with no contribution due to electronic conduction. The ionic transference number was determined to be unity from the oxygen-air gas concentration cell and the aluminum concentration cell method.