Kinetic modeling of near-interface defect segregation during thermal annealing of oxygen-conducting solid electrolytes

Solid electrolytes are widely employed in devices for energy storage and conversion. Extended defects (grain boundaries, surfaces and dislocations) can generate substantial resistance to ionic transport due to defect segregation. When synthesized through solid state reaction or sintered from powders, solid electrolytes go through thermal annealing processes at high temperatures. It is during these annealing phases that cation transport becomes fast enough to affect the distribution of cation defects near the interface. We developed a kinetic model of the annealing process as it affects the near-interface defect behavior based on the Poisson-Cahn model for predicting defect segregation behavior in concentrated solid solutions. Taking the fluorite-structured solid solution CeO2-Gd2O3 as a model system, results reveal that dopant profiles approach equilibrium on a timescale of seconds at 1300 °C and 20%, 1% and 0.1% dopant cation concentration. At lower temperatures, the dopant profile developed much more slowly. The quench temperature is predicted to be around 900 °C, where it requires > 15 h for the dopant profile to reach equilibrium.