Influence of Nano-Structural Feature on Electrolytic Properties of Gd Doped CeO₂ Solid Electrolytes

Abstract

Doped ceria (CeO₂) compounds are fluorite type oxides which show oxide ionic conductivity higher than yttria stabilized zirconia, in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for ‘low (500°-650°C)’ or ‘intermediate (650°-800°C)‘ temperature operation of solid oxide fuel cells (SOFCs). In this study, the authors prepared Gd_xCe_1-xO_2-δ (x=0.1, 0.15, 0.21, and 0.25) and Gd/Sr co-doped CeO₂ [(Gd_0.8Sr_0.2)_0.175Ce_0.825O_1.895] specimens using carbonate co-precipitation method, in order to examine the influence of nano-structural feature on electrolytic properties in the sintered bodies. And the relationship between the microstructural feature in nano-scale and the conducting property in those electrolytes were examined. A diffuse scatter was observed in the background of selected area electron diffraction pattern recorded from all sintered bodies. In addition, all specimens had extra spots in the selected area electron diffraction patterns recorded from sintered bodies. The diffuse scatter means that coherent micro-domain with ordered structure is in the lattice. Extra spots indicate the growth of micro-domain. From the comparison of calculated electron diffraction patterns between fluorite structure and b-type rare earth structure, it is concluded that the structure of micro-domain is distorted b-type rare earth structure or b-type related structure. From the observation of high-resolution transmission electron microscope (HR-TEM), it is concluded that the conducting property in Gd doped CeO₂ and Gd/Sr co-doped systems was strongly influenced by the size of micro-domain with ordered structure. The conductivity in Gd_0.21Ce_0.79O_1.895 sintered body with big micro-domain was lower than that in (Gd_0.8Sr_0.2)_0.175Ce_0.825O_1.895 sintered body with small micro-domain. Therefore, the author concluded that domain control is a key for development of doped CeO₂ electrolytes.