abstract
The total conductivity and Seebeck coefficient of La2Ni0.9Fe0.1O4+delta with K2NiF4-type structure, studied in the oxygen partial pressure range from 10(-5) to 0.5 atm at 973-1223 K, were analyzed in combination with the steady-state oxygen permeability, oxygen non-stoichiometry and Mossbauer spectroscopy data in order to examine the electronic and ionic transport mechanisms. Doping of La2NiO4+delta with iron was found to promote hole localization on nickel cations due to the formation of stable Fe3+ states, although the electrical properties dominated by p-type electronic conduction under oxidizing conditions exhibit trends typical for both itinerant and localized behavior of the electronic sublattice. The segregation of metallic Ni on reduction, which occurs at oxygen chemical potentials close to the low-p(O-2) stability boundary of undoped lanthanum nickelate, is responsible for the high catalytic activity towards partial oxidation of methane by the lattice oxygen of La2Ni0.9 Fe0.1O4+delta as revealed by thermogravimetry and temperature-programmed reduction in dry CH4-He flow at 573-1173 K. A model for the oxygen permeation fluxes through dense La2Ni0.9Fe0.1O4+delta ceramics, limited by both bulk ionic conduction and surface exchange kinetics, was proposed and validated. (c) 2008 Elsevier Inc. All rights reserved.
keywords
TRANSPORT-PROPERTIES; ELECTROCHEMICAL-BEHAVIOR; METHANE OXIDATION; PEROVSKITE-TYPE; NONSTOICHIOMETRY; LA2NIO4+DELTA; STABILITY; DIFFUSION; OXIDES; CONDUCTORS
subject category
Chemistry
authors
Kharton, VV; Tsipis, EV; Naumovich, EN; Thursfield, A; Patrakeev, MV; Kolotygin, VA; Waerenborgh, JC; Metcalfe, IS
our authors
Vladislav Kharton
Invited Principal ResearcherGroups