Abstract
The application of double perovskite cobaltites BaLnCo2O6−δ (Ln = lanthanide element) in electrochemical devices for energy conversion requires control of their properties at operating conditions. This work presents a study of a series of BaLnCo2O6−δ (Ln = La, Pr, Nd) with a focus on the evolution of structural and electrical properties with temperature. Symmetry, oxygen non-stoichiometry, and cobalt valence state have been examined by means of Synchrotron Radiation Powder X-ray Diffraction (SR-PXD), thermogravimetry (TG), and X-ray Absorption Spectroscopy (XAS). The results indicate that all three compositions maintain mainly orthorhombic structure from RT to 1000 °C. Chemical expansion from Co reduction and formation of oxygen vacancies is observed and characterized above 350 °C. Following XAS experiments, the high spin of Co was ascertained in the whole range of temperatures for BLC, BPC, and BNC.
Highlights
The double perovskite cobaltites BaLnCo2 O6-δ have been a subject of research attention in recent years due to their transport properties and possible application as electrodes in electrochemical devices for energy conversion
The polycrystalline BaLnCo2 O6-δ samples used in this study were prepared through a conventional solid-state reaction
The structure of double perovskite cobaltites has been the subject of numerous studies [7,8,9,10,11,12]
Summary
The double perovskite cobaltites BaLnCo2 O6-δ (where Ln is a lanthanide) have been a subject of research attention in recent years due to their transport properties and possible application as electrodes in electrochemical devices for energy conversion. The substantial number of oxygen vacancies in oxygen-deficient layers of LnOδ is believed to be beneficial for fast oxygen ion diffusion in these materials, while an overlap of Co3d and O2p orbitals in the Co-O slabs is favorable for enhanced electronic transport [1,2]. The flexibility of the double perovskite structure allows for substantial variations in oxygen non-stoichiometry and effective cobalt valence state, giving rise to high mixed ionic and electronic conductivity and fast surface kinetics [3]. We report the influence of temperature on structure and oxygen non-stoichiometry for a series of BaLnCo2 O6−δ compositions. In combination with thermogravimetry (TG), thermal and chemical unit cell expansion has been established for
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