Oxygen nonstoichiometry and ionic transport in La2Ni(Fe)O4 + δ

The steady-state oxygen permeation fluxes through dense La2NiO4 + δ and La2Ni0.9Fe0.1O4 + δ ceramics, studied at 973–1223 K for membrane thickness range 0.6 to 2.0 mm, are limited by both bulk ambipolar conductivity and surface exchange kinetics. The permeability data, in combination with total conductivity and equilibrium p(O2)–T–δ diagrams, were used in numerical regression analysis to extract the local chemical potential gradients, defect concentrations, partial conductivities and exchange rates. Doping with iron was found to increase oxygen-ion mobility in K2NiF4-type lanthanum nickelate at 1173–1223 K, whilst activation energies remain essentially similar, 69–80 kJ/mol. At lower temperatures, the surface kinetics and ionic transport in La2Ni0.9Fe0.1O4 + δ become both slower than those in La2NiO4 + δ. Possible defect-interaction and exchange mechanisms relevant to this behavior are briefly discussed.