Grain boundary segregation and its influences on ionic conduction properties of scandia doped zirconia electrolytes

Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper, ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 °C were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size. However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc³⁺ is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature.