Mechanochemical synthesis and ionic conductivity in the Gd ₂(Sn_1-yZr_y)₂O ₇ (0≤y≤1) solid solution

Several compositions within the Gd₂(Sn_{1- y}Zr_y)₂O₇ solid solution with a pyrochlore-type of structure, have been prepared at room temperature in a planetary ball mill starting from stoichiometric mixtures of the constituent oxides, SnO₂, ZrO₂ and Gd₂O₃. Phase evolution in the powder mixtures as a function of composition and milling time was followed by X-ray diffraction (XRD) finding out that after 18 h, every mixture consist of a single phase. Mechanically activated chemical reaction takes place after an intial step of particle size refinement and polymorphic transformation of C-Gd₂O₃. We have performed Impedance Spectroscopy measurements to investigate oxygen ion dynamics in the series and conclude that Zr substitution for Sn hardly modifies the importance of ion-ion correlations in the oxygen diffusion process. We also estimate from conductivity measurements the value of the microscopic activation energy needed for independent ion hopping, which is found to be 0.56±0.06 eV, independent of Zr content.