Abstract
Codoping ceria with rare earth elements has been shown to enhance grain ionic conductivity above that of singly doped materials. However, our recent work using a codoping scheme with Sm3+ and Nd3+ showed that 1:1 codoping results in conductivity intermediate between the respective singly doped samples, with Nd-doped ceria being higher than Sm- and Gd-doped. More recent studies have shown that small amounts (2–3%) of a second dopant can significantly enhance conductivity. Here we apply this scheme to the SmxNdyCe0.9O2−δ system with varying x/y codopant ratio. Samples were prepared using solid state reactions and conductivity measurements were done using two-point ac electrochemical impedance spectroscopy from 250–700 °C. Activation energy values were calculated from Arrhenius plots and increase as dopants shift from pure Sm3+ to pure Nd3+ in agreement with literature and the effective index. More importantly, the results of this study conclude that codopant ratio (x/y) variations within the SmxNdyCe0.9O2−δ system does not lead to significant conductivity changes and thus it constitutes a versatile system impervious to potential performance degradation due to preferential dopant segregation and redistribution.
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