Methods of isotopic relaxations for estimation of oxygen diffusion coefficients in solid electrolytes and materials with mixed ionic-electronic conductivity

Theoretical basis of isotopic oxygen exchange in a gas-solid oxide system are considered. A generalized model is suggested that accounts for diffusion of tracer oxygen atoms and allows within a single approach to perform numeric analysis of isotope experiments implemented in reactors of various types and in different temperature modes. It is shown that when C¹⁸O₂ is used as an isotopic reagent, the oxygen exchange rate on the metal oxide surface increases manifold (as compared to ¹⁸O₂), which allows determining more precisely diffusion limitations in case of isotopic exchange of oxygen in the oxide bulk. Estimates of oxygen self-diffusion coefficients are obtained in dispersed systems based on doped cerium-zirconium oxides with a fluorite-type structure, doped lanthanum silicates with an apatite-type structure, and also mixed praseodymium nickelates-cobaltites and their composites with yttrium-doped ceria.