Effect of cationic order–disorder on the transport properties of LaBaCo₂O_6–δand La_0.5Ba_0.5CoO_3–δperovskites

Abstract

A‐site cationic ordered LaBaCo2O6−δ and disordered La0.5Ba0.5CoO3−δ perovskite phases were obtained by solid state reaction. Their structural properties were studied at room temperature and 673 K, by combining powder diffraction techniques, X‐ray diffraction and neutron powder diffraction with an independent determination of the oxygen content of the samples by thermogravimetry. La0.5Ba0.5CoO3−δ exhibits cubic symmetry with cations randomly distributed, whereas LaBaCo2O6−δ shows tetragonal symmetry with the La3+ and Ba2+ ions distributed in alternating layers. The diffraction data were analyzed using the Rietveld method and different structural and microstructural models. Bond valence and Fourier methods were used to determine bond distances and neutron/electron density maps. LaBaCo2O6−δ exhibits a higher concentration of oxygen vacancies than La0.5Ba0.5CoO3−δ, because the O atom is weakly bonded to the LaO layers. The anisotropic atomic displacement and the neutron density distribution suggest a two‐dimensional O‐migration path for LaBaCo2O6−δ and a three‐dimensional path for La0.5Ba0.5CoO3−δ.The mechanism of electrical conductivity is via electron holes with high mobilities (μLa0.5Ba0.5CoO3−δ = 2.49 cm2 V−1 s−1 and μLaBaCo2O6−δ = 1.48 cm2 V−1 s−1 at room temperature) and low activation energy (EaLaBaCo2O6−δ = 0.019 eV and EaLa0.5Ba0.5CoO3−δ = 0.030 eV). It has also been found that the higher electronic and ionic conductivities in La0.5Ba0.5CoO3−δ compared to those in LaBaCo2O6−δ are due to the higher dimensionality of transport and to greater overlapping between the Co 3d and O 2p orbitals.

Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo2O5+δ Double Perovskite

“…Above this temperature region, the electric conductivity of La 0.5 Ba 0.5 CoO 3-δ and LaBaCo 2 O 5+δ is consistent with previous reports on p-type semiconductor behavior [32,33,34]. Assuming LaCoO 3 as the host material, substitution of Ba into LaCoO 3 can be described by defect equilibrium (2), using Kröger–Vink notation [33]: $BaCo{O}_3 \stackrel{LaCo{O}_3}{\to } B{a}_{La}^{\prime }+C{o}_{Co}^{.}+3 O_O^x$where the negatively effective charged $B{a}_{La}^{\prime }$ represents Ba 2+ on La 3+ sites and the positively effective charged $C{o}_{Co}^{.}$represents the change of oxidation state of Co from Co 3+ in LaCoO 3 to Co 4+ in BaCoO 3 .…”

“…The oxygen content is critical to promote A-site cation ordering in LaBaCo 2 O 5+δ [15,34,35], but the necessary level of oxygen vacancies that is needed in order to promote A-site cation ordering is not clear from previous studies. Here, we obtained the A-site cation ordered LaBaCo 2 O 5+δ from the disordered La 0.5 Ba 0.5 CoO 3-δ .…”

The Superior Properties of La0.6Ba0.4CoO3-δThin Film Electrodes for Oxygen Exchange in Comparison to La0.6Sr0.4CoO3-δ

“…For both polycrystalline target diffraction patterns all visible peaks could be assigned to the perovskite phases and no sign of impurities was found. Vacancy ordering in LBC (annealed at high temperatures in Ar atmosphere) has been reported 37 for a similar cation stoichiometry (LaBaCo 2 O 6-δ ). However, this tetragonal phase was not observed due to the oxidizing conditions applied during target preparation.…”

Effect of Cation Ordering on the Performance and Chemical Stability of Layered Double Perovskite Cathodes

“…Both the ordered and disordered variants demonstrate low polarization resistances at temperatures as low as 600 °C (<0.2 Ω·cm 2 ) due to the excellent mixed conducting (electron hole and oxide-ion) nature of the material. In addition, Garces et al have studied the influence of the A-site cation ordering on the mixed electronic and oxide-ion conducting properties in this system [29,30]. They obtained a noticeable improvement of performance with A-site cation ordering (0.35 Ω·cm 2 for La 0.5 Ba 0.5 CoO 3−δ vs. 0.12 Ω·cm 2 for LaBaCo 2 O 5+δ at 600 °C in air).…”