Electrical conductivity versus dopant ionic radius studies in zirconia- and ceria-based, solid oxide fuel cell electrolyte systems had shown that O-ion conductivity was highest when the host and dopant ions were similar in size. Under these conditions, it was thought that the conduction paths within the crystal lattice become less distorted. Binary ZrO2–M2O3 unit cells were here expanded, via the partial substitution of Ce+4 for Zr+4 into the lattice, in an attempt to identify new ternary zirconia/ceria-based electrolyte systems with enhanced electrical conductivity. The compositions Zr0.75Ce0.08M0.17O1.92 (M = Nd, Sm, Gd, Dy, Ho, Y, Yb, Sc) were prepared by using traditional solid state techniques. Bulk phase characterization and precise lattice parameter measurements were performed with X-ray diffraction techniques. Four-probe direct-current conductivity measurements between 400 and 900C showed that the dopant-ion radius influenced electrical conductivity. The conductivity versus dopant-ion radius trends previously observed in zirconia-based, binary systems were clearly apparent in the ternary systems investigated here. The addition of ceria was found to have a negative influence on the electrical conductivity at 400 to 900C. It was suggested that distortion of the O-ion conduction path by the presence of the larger M3+ and Ce4+ species (relative to Z4+) was the reason for the decreasing electrical conductivity as a function of increasing dopant size and ceria addition, respectively.

Investigation of Electrical Conductivity as a Function of Dopant-Ion Radius in the Systems Zr0.75Ce0.08M0.17O1.92 (M = Nd, Sm, Gd, Dy, Ho, Y, Er, Yb, Sc). J.Kimpton, T.H.Randle, J.Drennan: Solid State Ionics, 2002, 149[1-2], 89-98