We have prepared different compositions in the Gd 2−y La y Zr 2 O 7 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 1200 • C. Ionic conductivity was found to be thermally activated and almost independent of La content for 0 y 1, since the pre-exponential factor decreases as structural ordering increases; however, there is a concomitant decrease of the activation energy E dc for oxide-ion diffusion, from E dc = 1.13 ± 0.02 eV for the anion-deficient fluorite Gd 2 Zr 2 O 7 to E dc = 0.85 ± 0.03 eV for the partially ordered pyrochlore-type Gd 1.2 La 0.8 Zr 2 O 7 . Electrical conductivity relaxation is well described by a Kohlrausch-Williams-Watts (KWW) function of the form = exp(−(t/τ ) 1−n ), 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.

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Different compositions in the pyrochlore-type Gd 2-y La y Zr 2 O 7 solid solution (0 ≤ y ≤ 1) were prepared at room-temperature 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 long-range ordering of cations and anion vacancies characteristic of pyrochlores was observed in all cases after firing the samples at 1500°C. Interestingly, activation energy for oxygen migration in the series decreases as La-content increases, from 1.13 eV for Gd 2 Zr 2 O 7 to 0.81 eV for GdLaZr 2 O 7 , whereas ionic conductivity was found to be almost La-content independent, at least for y ≤ 0.8 at T = 500°C and y ≤ 0.4 at T = 800°C. These results are explained in terms of weaker ion-ion interactions in better ordered structures (i.e., as La-content increases) and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions. Keywords: Pyrochlores; mechanical milling; zirconates; SOFCs; lanthanum.Síntesis y propiedades eléctricas de la solución sólida Gd 2-y La y Zr 2 O 7 con estructura de tipo pirocloro Partiendo de mezclas estequiométricas de los óxidos correspondientes, se prepararon por molienda mecánica y a temperatura ambiente diferentes composiciones en la solución sólida Gd 2-y La y Zr 2 O 7 (0 ≤ y ≤ 1) con estructura de tipo pirocloro y conductora de iones oxígeno. Independientemente del contenido de lantano, los polvos extraídos del molino presentaron difractogramas similares al de una fluorita no estequiométrica aunque en todos los casos, el tratamiento térmico a 1500°C indujo la aparición del ordenamiento de largo alcance de cationes y vacancias aniónicas característico de pirocloros. La energía de activación para el proceso de migración de iones oxígeno en la serie disminuye a medida que se incrementa el contenido de lantano, desde 1.13 eV de Gd 2 Zr 2 O 7 hasta 0.81 eV de GdLaZr 2 O 7 , mientras que la conductividad resultó ser prácticamente independiente del mismo hasta y ≤ 0.8 para T = 500°C e y ≤ 0.4 para T = 800°C. Estos resultados se explican en términos de una menor interacción entre portadores de carga en las estructuras más ordenadas (a medida que se incrementa el contenido de La) y subraya la influencia del orden/desorden estructural en la dinámica de iones móviles.