High-trivalent rare earth ion conduction in solids based on NASICON-type phosphate

Trivalent rare earth ion conductors of the (R0.05Zr0.95)(80/79)Nb(PO4)(3) (R: rare earths) series with NASICON-type structures were successfully prepared and the optimum size of ion-conducting pathways for rare earth ions in (R0.05Zr0.95)(80/79)Nb(PO4)(3) solids was investigated. The most suitable ion-conducting pathway for rare earth ion conduction in this series was realized for R = Dy and the highest conductivity of 3.2 x 10(-4) Scm(-1) at 600 degrees C was obtained for (Dy0.05Zr0.95)(80/79)Nb(PO4)(3) solids. Since R3+ ion conduction was strongly dependent on the ratio of conducting R3+ ion size to crystal lattice size (VR3+/V-lattice; we denote this ratio as A ratio in this article), it was clear that the A ratio is a key factor to optimize R3+ ion conduction in NASICON-type structures.