Effect of Dopant and Impurity Segregation on the Ionic Conductivity of Doped Ceria Electrolytes

Doped ceria is a good electrolyte candidate for intermediate temperature solid oxide fuel cells (IT-SOFC) because of its enhanced ionic conductivity. Segregation of dopants and impurities at grain boundaries may degrade the performance of these materials. This grain boundary segregation can be mitigated through manipulation of processing conditions. Recent studies have shown that, at 550°C, Sm_0.75Nd_0.75CeO_2-δ made by co-precipitation from nitrates followed by microwave sintering exhibits enhanced ionic conductivity (2.8 × 10^-3 S·cm^-1) as compared to the ball milled and conventionally sintered (1.9 × 10^-3 S·cm^-1) samples (1). Here we focus on the effects that the composition and processing have on the bulk and grain boundary contributions to ionic conductivity and gain a systematic understanding of the underlying processes. Scanning electron microscopy (SEM), electron energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD) studies indicate that the co-precipitated and microwave sintered samples exhibit smaller grain size, lower impurity content and less segregation at grain boundaries and triple point junctions as compared to conventional solid state processing route. These results are correlated with ionic conductivity data obtained from electrochemical impedance spectroscopy (EIS). 

REFERENCES:

1. S. Omar, “Enhanced Ionic Conductivity of Ceria-Based Compounds for the Electrolyte Application in SOFCs”, Ph.D. Dissertation, University of Florida (2008).