The effect of homovalent A-site substitutions on the ionic conductivity of pyrochlore-type Gd 2Zr 2O 7

Abstract

We evaluate in this work the effect of Gd substitution on the dc activation energy, E dc, and ionic conductivity of the pyrochlore-type gadolinium zirconate, P-Gd 2Zr 2O 7. Several compositions with the general formulae Gd 2− y Ln y Zr 2O 7 (Ln = Er 3+, Y 3+, Dy 3+, Sm 3+, Nd 3+ and La 3+) were prepared by mechanically milling and firing stoichiometric mixtures of the corresponding elemental oxides and their electrical properties analyzed as a function of frequency and temperature by using impedance spectroscopy. Whereas Gd substitution in P-Gd 2Zr 2O 7 by smaller lanthanides induces a pyrochlore to fluorite phase transition, using larger dopant cations yields partially disordered pyrochlores. Despite of higher structural disorder, ionic conductivity values measured for the fluorite-type materials are lower than those observed for pyrochlores whereas activation energies for oxygen migration in the series decrease monotonically as the average size of the A cation increases.