| Summary: | This work presents the results from a study of the structure and transport properties of Ca-doped La<sub>2</sub>NiO<sub>4+δ</sub>. La<sub>2−x</sub>Ca<sub>x</sub>NiO<sub>4+δ</sub> (<i>x </i>= 0–0.4) materials that were synthesized via combustion of organic-nitrate precursors and characterized by X-ray diffraction (XRD), in situ XRD using synchrotron radiation, thermogravimetric analysis (TGA) and isotope exchange of oxygen with C<sup>18</sup>O<sub>2</sub>. The structure was defined as orthorhombic (<i>Fmmm</i>) for <i>x </i>= 0 and tetragonal (<i>I4</i>/<i>mmm</i>) for <i>x </i>= 0.1–0.4. Changes that occurred in the unit cell parameters and volume as the temperature changed during heating were shown to be caused by the excess oxygen loss. Typical for Ruddlesden–Popper phases, oxygen mobility and surface reactivity decreased as the Ca content was increased due to a reduction in the over-stoichiometric oxygen content with the exception of <i>x</i> = 0.1. This composition demonstrated its superior oxygen transport properties compared to La<sub>2</sub>NiO<sub>4+δ</sub> due to the enhanced oxygen mobility caused by structural features. Electrochemical data obtained showed relatively low polarization resistance for the electrodes with a low Ca content, which correlates well with oxygen transport properties.
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