Various compositions of the Gd2-yLayZr2O7 solid solution were prepared by mechanically milling stoichiometric mixtures of the corresponding oxides. Regardless of their La content, as-prepared powder samples consisted of single-phase anion-deficient fluorite materials, although the long-range ordering of cations and anion vacancies which was characteristic of pyrochlores was observed for y ≥ 0.4 after post-milling heat treatment at 1200C. The ionic conductivity was found to be thermally activated and almost independent of the La content for 0 ≤ y ≤ 1; since the pre-exponential factor decreased as structural ordering increased. However, there was a concomitant decrease in the activation energy for oxide-ion diffusion: from 1.13eV for the anion-deficient fluorite Gd2Zr2O7 to 0.85eV for the partially ordered pyrochlore-type Gd1.2La0.8Zr2O7. Electrical conductivity relaxation was well-described by a Kohlrausch–Williams–Watts function of the form, Φ = exp(-(t/τ)1-n), where the fractional exponent n decreased as the La content (ordering) increased. The results were explained in terms of weaker ion–ion interactions in the better ordered structure, and highlighted the importance of structural ordering/disordering in determining the dynamics of mobile O ions.

Effect of La Substitution for Gd in the Ionic Conductivity and Oxygen Dynamics of Fluorite-Type Gd2Zr2O7. J.A.Díaz-Guillén, M.R.Díaz-Guillén, J.M.Almanza, A.F.Fuentes, J.Santamaría, C.León: Journal of Physics - Condensed Matter, 2007, 19[35], 356212 (11pp)