Correlation between Structural and Transport Properties of Ca-Doped La Nickelates and Their Electrochemical Performance

• Main Authors: Elena Pikalova, Vladislav Sadykov, Ekaterina Sadovskaya, Nikita Yeremeev, Alexander Kolchugin, Alexander Shmakov, Zakhar Vinokurov, Denis Mishchenko, Elena Filonova, Vladimir Belyaev
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Crystals
• Subjects: La₂NiO_4+δ; Ca doping; isotope exchange; synchrotron radiation studies; oxygen mobility; polarization resistance
• Online Access: https://www.mdpi.com/2073-4352/11/3/297

This work presents the results from a study of the structure and transport properties of Ca-doped La₂NiO_4+δ. La_2−xCa_xNiO_4+δ (<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 C¹⁸O₂. 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 La₂NiO_4+δ 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.