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 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 Sm_{2 + x}Zr_{2 − x}O_{7 − x/2} with 26.6, 33.3, 35.5, 37, and 40 mol % Sm₂O₃ prepared at 1450, 1530, and 1600°C. Eu_{2 + x}Zr_{2 − x}O_{7 − x/2} and Gd_{2 + x}Zr_{2 − x}O_{7 − 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 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 Ln₂Zr₂O₇ (Ln = Sm-Gd) pyrochlores prepared at 1600°C, owing to the optimal concentration of Ln_Zr + Zr_Ln antistructure pairs (∼5–22%). The grains in the ceramic samples studied range in size from 0.5 to 2 µm.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 975–984.Original Russian Text Copyright © 2005 by Shlyakhtina, Kolbanev, Knotko, Boguslavskii, Stefanovich, Karyagina, Shcherbakova.