Ionic conductivity of Ln2+xZr2-xO7-x/2 (Ln = Sm-Gd) solid solutions

The electrical conductivity of Ln(2+x)Zr(2-x)O(7-x/2) (Ln = Sm-Gd) solid solutions prepared from mechanically activated Ln(2)O(3) and ZrO2 is shown to correlate with their structural properties. In the three systems, the x-T regions are determined in which electrical transport is dominated by oxygen-ion conduction. In the Sm2O3-ZrO2 system, ionic conductivities from 5 x 10(-4) to 6 x 10(-3) S/cm at 740 degrees C are found in Sm2+xZr2-xO7-x/2 with 26.6, 33.3, 35.5, 37, and 40 mol % Sm2O3 prepared at 1450, 1530, and 1600 degrees C. Eu2+xZr2-xO7-x/2 and Gd2+xZr2-xO7-x/2 containing 33.3 to 37 mot % Ln(2)O(3) have 740 degrees C ionic conductivities of 10(-3) to similar to 7.5 x 10(-3) and 10(-3) to 7 x 10(-3) S/cm, respectively. The activation energy of conduction in Ln(2+x)Zr(2-x)O(7-x/2) (Ln = Sm-Gd), E-a = 0.84-1.04 eV, increases with the atomic number of Ln and x. The highest ionic conductivity is offered by the stoichiometric Ln(2)Zr(2)O(7) (Ln = Sm-Gd) pyrochlores prepared at 1600 degrees C, owing to the optimal concentration of Ln(Zr) + Zr-Ln antistructure pairs (similar to 5-22%). The grains in the ceramic samples studied range in size from 0.5 to 2 mu m.