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. Trivale nt ions especially for aluminum where the polarizability is considerab ly low, are strongly bonded in a crystal lattice and have been believe d to be unlikely to exhibit migration in solids because of high electr ostatic interaction with the surrounding skeleton structure. The mater ial, 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 mobil e species, Al3+, as much as possible. The ionic conduction characteris tics of Al-2(WO4)(3) were investigated by means of electrolysis and el ectromotive force measurement by constructing an aluminum concentratio n cell. The typical electrical conductivity of Al-2(WO4)(3) was, appro ximately 2 x 10(-5) S cm(-1) at 800 degrees C. The dc electrolysis dat a strongly support the conclusion that ionic Al3+ is the mobile specie s in Al-2(WO4)(3). By further electrochemical measurements, it was con firmed that the mobile species was aluminum ion in a trivalent state w ith no contribution due to electronic conduction. The ionic transferen ce number was determined to be unity from the oxygen-air gas concentra tion cell and the aluminum concentration cell method.