Oxide ionic transport features in Gd-doped La nickelates

In this work new RP materials of the La2-xGdxNiO4+delta series were synthesized and their structural features, oxygen stoichiometry and transport properties were studied by X-ray diffraction, TGA, mass relaxation method and oxygen isotope exchange with (CO2)-O-18 in a flow reactor. According to XRD data, La2-xGdxNiO4+delta (x = 0.0; 0.2; 0.4) are single-phase samples with a tetragonal structure. Doping with Gd resulted only in the insignificant increase of the interstitial oxygen content (delta changes in the range of 0.13-0.15). A high oxygen mobility was demonstrated: at 700 degrees C D-chem similar to 10(-5) cm(2)/s (mass relaxation data) and self-diffusion coefficient D* similar to 10(-8) cm(2)/s (oxygen isotope exchange data). Such characteristics are determined by the cooperative mechanism of oxygen migration involving both regular and highly-mobile interstitial oxygen. Gd doping, however, resulted in non-uniformity of the oxygen migration routes. To describe this feature, a mathematical model has been developed including a slow exchange between neighboring oxide anions. Oxygen mobility decreases with increasing Gd content.