Trivalent rare earth ion conduction in the rare earth tungstates with the Sc2(WO4)3-type structure

To realize a trivalent ion conduction in solids, the Sc-2(WO4)(3)-type structure was chosen on the basis of the mobile trivalent ions and the structure which reduces the electrostatic interaction between the framework and the mobile trivalent ionic species as much as possible. The typical conductivity of the rare earth tungstates R-2(WO4)(3) (R = Sc, Y, and Er-Lu) with the Sc-2(WO4)(3)-type structure was found to be on the order of 10(-5) S cm(-1) at 600 degrees C. Among the rare earth tungstates, Sc-2(WO4)(3) (sigma(600 degrees C) = 6.5 X 10(-5) S cm(-1), E-a = 44.1 kJ mol(-1)) was found to be the most suitable size for the ionic conduction with regard to the relation between the mobile ion radius and the lattice size. The rare earth ion conducting characteristics were investigated by means of the rare earth concentration cell measurements and de electrolyses. The electromotive force measurements with the Sc-Y binary alloy and the yttrium tungsten bronze as the electrodes strongly suggest the possibility of the trivalent ion conduction of rare earths such as SC3+ and Y3+. Furthermore, by the de electrolysis, the mobile species was clarified to be the rare earth ions SC3+ and Y3+ in the rare earth tungstates with the Sc-2(WO4)(3)-type structure.