Ionic conductivity of Gd2GaSbO7–Gd2Zr2O7 solid solutions with structural disorder

A new pyrochlore solid solution family, Gd2GaSbO7–Gd2Zr2O7 (Gd2(GaSb)1−xZr2xO7; GGSZ) exhibiting oxygen ion conduction due to structural disorder, has been investigated. In this study, the ionic conductivity and structural disorder of GGSZ were analyzed by fitting the electrical conductivity as functions of PO2 and temperature to a defect chemical model based on oxygen Frenkel disorder. GGSZ with x=0.8 exhibited an ionic conductivity of 2.14×10−3 S/cm at 1000°C, and an activation energy of 0.51±0.003 eV. The Frenkel disorder enthalpy was found to decrease rapidly with increasing x, dropping to ≈0 eV at x=0.8. The oxygen vacancy mobility was found to increase with x which, together with the increase in carrier density, led to a very sharp increase in ionic conductivity at higher values of x. The GGSZ system is compared with the Gd2Ti2O7–Gd2Zr2O7 and Gd2Sn2O7–Gd2Zr2O7 systems also known to exhibit a structural disorder correlated ionic conductivity.