Oxygen ion transport in La2NiO4-based ceramics

Abstract

The solid solutions La ₂ Ni _1–x Fe _x O _4+δ (x = 0.02 and 0.10), La _1.9 Sr _0.1 Ni _{1 – x} Fe _x O _{4 + δ} (x = 0.02 and 0.10) and La ₂ Ni _0.88 Fe _0.02 Cu _0.10 O _4+δ with the tetragonal K ₂ NiF ₄ -type structure were prepared by a standard ceramic technique. The thermal expansion coefficients of the ceramic materials, calculated from dilatometric data, are in the range (10.5–13.2) × 10 ^–6  K ^–1 at 300–1100 K. Oxygen permeation fluxes through dense La ₂ NiO _{4 + δ} -based membranes at 970–1170 K were found to be limited by both surface exchange and bulk ionic transport, whereas the limiting effect of the oxygen interphase exchange increases with decreasing oxygen pressure at the membrane permeate side and with decreasing temperature. Applying porous cermet layers of dispersed platinum and praseodymium oxide onto the membrane surface results in enhanced permeation fluxes. The maximum oxygen permeability was found for the La ₂ Ni _0.98 Fe _0.02 O _4+δ and La ₂ Ni _0.88 Fe _0.02 Cu _0.10 O _4+δ solid solutions; oxygen permeability data demonstrated that a vacancy diffusion mechanism and oxygen interstitial migration make significant contributions to the total ionic conductivity.