Ionic conductivity of Gd2GaSbO7-Gd2Zr2O7 solid solutions with structural disorder

A new pyrochlore solid solution family, Gd2GaSbO7-Gd2Zr2O7 (Gd-2(GaSb)(1-x) Zr2xO7; 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 f unctions 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 x 10(-3) S/cm at 1000 degreesC, and an activation energy of 0.51+/-0.003 e V. The Frenkel disorder enthalpy was found to decrease rapidly with increas ing x, dropping to approximate to0 eV at x = 0.8. The oxygen vacancy mobili ty was found to increase with x which, together with the increase in carrie r density, led to a very sharp increase in ionic conductivity at higher val ues of x. The GGSZ system is compared with the Gd2Ti2O7-Gd2Zr2O7 and Gd2Sn2 O7-Gd2Zr2O7 systems also known to exhibit a structural disorder Correlated ionic conductivity. (C) 2000 Elsevier Science B.V. All rights reserved.