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. Effect of La Substitution for Gd in the Ionic Conductivity and Oxygen Dynamics of Fluorite-type Gd2Zr2O7. Journal of Physics: Condensed Matter (ISSN: 0953-8984). 2007, Vol. 19, p. 356212-1-2007.
We have prepared different compositions in the Gd2-yLayZr2O7 solid solution by mechanically milling stoichiometric mixtures of the corresponding oxides. Irrespective of their lanthanum content, as-prepared powder samples consist of single-phase anion deficient fluorite materials, although the long-range ordering of cations and anion vacancies characteristic of pyrochlores was observed for y < 0.4 after post-milling thermal treatments at 1200ºC. Ionic conductivity was found to be thermally activated and almost La-content independent for 0 ≤ y ≤ 1, since the pre-exponential factor decreases as structural ordering increases, but there is a concomitant decrease of the activation energy Edc for oxide-ion diffusion, from Edc = 1.13 ± 0.02 eV for the anion deficient fluorite Gd2Zr2O7, to Edc = 0.85 ± 0.03 eV for the partially ordered pyrochlore-type Gd1.2La0.8Zr2O7. Electrical conductivity relaxation is well described by a Kohlrausch-Williams-Watts (KWW) function where the fractional exponent n decreases as the La-content (ordering) increases. These results are explained in terms of weaker ion-ion interactions in the better ordered structure and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.
We have prepared different compositions in the Gd2-yLayZr2O7 solid solution by mechanically milling stoichiometric mixtures of the corresponding oxides. Irrespective of their lanthanum content, as-prepared powder samples consist of single-phase anion deficient fluorite materials, although the long-range ordering of cations and anion vacancies characteristic of pyrochlores was observed for y < 0.4 after post-milling thermal treatments at 1200ºC. Ionic conductivity was found to be thermally activated and almost La-content independent for 0 ≤ y ≤ 1, since the pre-exponential factor decreases as structural ordering increases, but there is a concomitant decrease of the activation energy Edc for oxide-ion diffusion, from Edc = 1.13 ± 0.02 eV for the anion deficient fluorite Gd2Zr2O7, to Edc = 0.85 ± 0.03 eV for the partially ordered pyrochlore-type Gd1.2La0.8Zr2O7. Electrical conductivity relaxation is well described by a Kohlrausch-Williams-Watts (KWW) function where the fractional exponent n decreases as the La-content (ordering) increases. These results are explained in terms of weaker ion-ion interactions in the better ordered structure and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.