Trivalent Aluminum Ion Conducting Characteristics in Al2(WO4)3 Single Crystals

Single crystals of the trivalent Al 3+ ion conductor Al 2 (WO 4 ) 3 were grown by the Czochralski (CZ) method. The ionic conductivity in the a -, b -, and c -axis directions was determined and Al 3+ ion conduction in the direction of the b -axis was concluded to be the most suitable pathway for ion migration in the tungstate grains. The ionic conductivities in the a- and c -axis directions were 0.3 and 10 -2 times lower than the conductivity in the b -axis. Consistent with this observation, the lowest activation energy ( E a ) for Al 3+ ion migration was obtained for the b -axis direction. The E a of the conductivity in the direction of the c -axis was almost comparable to that of the polycrystalline samples and the E a of the Al 3+ ionic conduction in the grains of this material was explicitly verified to be controlled by the Al 3+ ionic migration in the c -axis direction. The Al 3+ ion conductivity of the polycrystalline sample was higher in the higher temperature region, indicating that the conductivity in the grain boundaries enhances the total Al 3+ ion conductivity to a considerable extent. From the oxygen pressure dependencies of the electrical conductivity and the polarization behavior, the single crystals were demonstrated to be pure Al 3+ ionic conductors showing an anisotropic ion conducting behavior.