New trivalent rare earth ion (La, Nd, Gd) conducting solid electrolytes

New trivalent rare earth ion conducting (RxZr1-x)(4/(4-x))Nb(PO4)(3) (R: La, Nd, Gd) solid electrolytes based on the NASICON type structure, which have a three-dimensional network structure suitable for the R3+ ion conduction, were prepared and their ion conducting properties in their solids were investigated. The most suitable conducting path size for the R3+ ion conduction in the solids was identified from the relationship between the mobile ion size and the lattice volume. The typical ion conductivity of the rare earth phosphates was found to be in the order of 10(-4) S cm(-1) at 600 degrees C and the highest ion conductivity among the (RxZr1-x)(4/(4-x))Nb(PO4)(3) phosphate series was obtained for R = Nd. The conducting species in the (NdxZr1-x)(4/(4-x))Nb(PO4)(3) solid electrolyte was identified to be the trivalent Nd3+ ion by the AC conductivity measurements in various oxygen partial pressures and also by the DC electrolysis. (c) 2005 Elsevier B.V. All rights reserved.