Determination of inter-diffusion coefficients for the A- and B-site in the A2BO4 + δ (A = La, Nd and B = Ni, Cu) system

A- and B-site cation diffusion in the La2NiO4 + δ system was investigated by, respectively, La2NiO4 + δ–Nd2NiO4 + δ and La2NiO4 + δ–La2CuO4 + δ inter-diffusion couples, annealed 100–600 h in ambient air at 950–1300 °C. Concentration profiles of the inter-diffusing cations were obtained by means of Electron Probe Micro Analysis (EPMA) from cross-sections. These profiles were fitted to the solution of Fickʹs second law for constant source and to Whipple–Le Claireʹs equation from which bulk and grain boundary diffusion coefficients, respectively, were derived. The diffusivity of A- and B-site cations in the grain interiors (bulk) are essentially comparable, while grain boundary diffusion of the B-site cations is enhanced, around 5 orders of magnitude within the investigated temperature range. Element mapping of the cross-sections of La2NiO4 + δ–La2CuO4 + δ couples visualises the enhanced grain boundary diffusion of B-site cations. The activation energies are 275 ± 12 kJ/mol for A-site bulk diffusion, and 450 ± 20 and 125 ± 24 kJ/mol for B-site bulk and grain boundary diffusion, respectively.