Trivalent Aluminum Ionic Conduction in the Aluminum Tungstate−Scandium Tungstate−Lutetium Tungstate Solid Solution System

The solid solutions of the Al 2 (WO 4 ) 3 −Sc 2 (WO 4 ) 3 −Lu 2 (WO 4 ) 3 series which hold the Sc 2 (WO 4 ) 3 -type structure were prepared and their ionic conducting characteristics were investigated. The maximum electrical conductivity was obtained for the solid solution of (Al 2 (WO 4 ) 3 ) 0.1 −((Sc 0.5 Lu 0.5 ) 2 (WO 4 ) 3 ) 0.9 . By the measurements of the electrical conductivity dependencies on oxygen pressure and the polarization analyses, the mobile species in the solid solution was found to be only ionic and also oxide anion was eliminated from the candidates of the conducting ion species. Among the cation species in the solid solution, the mobile ion was demonstrated to be only Al 3+ ion and the rest of the cations such as Sc 3+, Lu 3+, and W 6+ functioned as lattice-forming ions with oxide anion from the electrolysis experiments. Here, the highest Al 3+ ion conduction was obtained in the Sc 2 (WO 4 ) 3 -type structure and the optimal lattice size for the Al 3+ ion migration in the Sc 2 (WO 4 ) 3 -type structure was identified.