The anisotropy of the oxygen anionic conductivity was measured for two mixed ionic electronic conducting (MIEC) oxides with the 2D K 2NiF4-type structure, i.e., Nd2NiO 4+δ and Pr2NiO4+δ, using high quality single crystals. Measurements of the oxygen diffusivity and surface exchange performed parallel and perpendicularly to the  direction, from 450 to 700 C, using the isotope exchange depth profile (IEDP) technique, combining 16O/18O exchange and secondary ion mass spectroscopy (SIMS) are reported. For both materials the diffusion is about 3 orders of magnitude higher along the (a,b)-plane compared to the perpendicular (c-axis) direction. These values are among the highest when compared to several state-of-the-art MIEC materials. The diffusion along the (a,b)-plane for Pr 2NiO4+δ is higher than that of Nd 2NiO4+δ due to a much lower diffusion activation energy (0.5 and 1.4 eV for Pr2NiO4+δ and Nd 2NiO4+δ, respectively). A large anisotropy is also observed in the surface exchange coefficient (k*) values for both materials, with (a,b)-plane coefficients being 1 to 1.5 orders of magnitude larger than those for the c-axis.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films
- Physical and Theoretical Chemistry