Quantifying the oxygen stoichiometry of Pr-doped ceria through X-ray diffraction

Recent studies on Pr-doped CeO$_{2}$ (PCO) model electrodes suggest that the fast oxygen surface exchange coefficient and high ionic conductivity of PCO hold the potential for a high performance air electrode material for solid oxide fuel cells (SOFCs).[1] PCO behaves as a mixed ionic-electronic conductor (MIEC) in air at elevated temperature due to the reduction of Pr$^{4+}$ to Pr$^{3+}$ and a concomitant polaronic conductivity σpol. In this study, we characterize the reduction behavior of PCO with different Pr contents in air using high temperature X-ray diffraction (HT-XRD) and compare the results to TGA measurements. Rietveld analysis of the HT-XRD data reveals a temperature-dependent micro-strain in the PCO lattice that we associate with lattice disorder due to the different ionic radii of Pr$^{4+}$ and Pr$^{3+}$. This allows us to identify the precise temperature at which the polaronic conductivity σpol is highest for a given Pr-content. We discuss the effect of the temperature dependence of σpol for air electrodes in the context of conductivity and impedance measurements.1. Chen, D., S.R. Bishop, and H.L. Tuller, Praseodymium-cerium oxide thin film cathodes: Study of oxygen reduction reaction kinetics. Journal of Electroceramics, 2012. 28(1): p. 62-69