Oxygen isotope exchange in La2NiO4±δ

Abstract

Oxygen surface exchange kinetics and diffusion have been studied by the isotope exchange method with gas phase equilibration using a static circulation experimental rig in the temperature range of 600–800 °C and oxygen pressure range of 0.13–2.5 kPa. A novel model which takes into account distributions of the dissociative adsorption and incorporation rates has been developed. The rates of the elementary stages have been calculated. The rate-determining stages for a La₂NiO_4±δ polycrystalline specimen have been discussed. The diffusion activation energies calculated using the gas phase equilibration method (1.4 eV) differ significantly from those calculated using isotope exchange depth profiling (0.5–0.8 eV), which was attributed to the influence of different oxygen diffusion pathways.