Two-fold stoichiometry relaxation - Simulated relaxation kinetics of ionic and electronic defect concentrations

The relaxation kinetics of defect concentrations in an oxide containing protons, oxygen vacancies, and holes after an increase of water partial pressure are simulated using materials parameters representative for perovskite proton conductors. Different regimes are identified (e.g. single-fold chemical diffusion of water at low pO2, two-fold relaxation at high pO2). It is shown that the analysis of ionic defect concentrations (which could be measured e.g. by thermogravimetry) and electronic defect concentrations (detectable by conductivity relaxation) yields different effective diffusion coefficients. Owing to the transition between different defect chemical and diffusion regimes, extracted effective activation energies are related to the fundamental transport parameters in a complex way.