Ionic Conductivity of Ln2 + x Zr2 − x O7 − x/2 (Ln = Sm-Gd) Solid Solutions

Abstract

The electrical conductivity of Ln2 + xZr2 − xO7 − x/2 (Ln = Sm-Gd) solid solutions prepared from mechanically activated Ln2O3 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 × 10−4 to 6 × 10−3 S/cm at 740°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°C. Eu2 + xZr2 − xO7 − x/2 and Gd2 + xZr2 − xO7 − x/2 containing 33.3 to 37 mol % Ln2O3 have 740°C ionic conductivities of 10−3 to ∼7.5 × 10−3 and 10−3 to 7 × 10−3 S/cm, respectively. The activation energy of conduction in Ln2 + xZr2 − xO7 − x/2 (Ln = Sm-Gd), Ea = 0.84–1.04 eV, increases with the atomic number of Ln and x. The highest ionic conductivity is offered by the stoichiometric Ln2Zr2O7 (Ln = Sm-Gd) pyrochlores prepared at 1600°C, owing to the optimal concentration of LnZr + ZrLn antistructure pairs (∼5–22%). The grains in the ceramic samples studied range in size from 0.5 to 2 µm.