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The origin of triple conductivity and water uptake in layered double perovskites: A case study on lanthanum-substituted GdBaCo2O6−δ.

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Title: The origin of triple conductivity and water uptake in layered double perovskites: A case study on lanthanum-substituted GdBaCo2O6−δ.
Authors: Malyshkin, Dmitry1,2 (AUTHOR) dmitry.malyshkin@urfu.ru, Novikov, Andrey1 (AUTHOR), Ivanov, Ivan1 (AUTHOR), Sereda, Vladimir1,2 (AUTHOR), Tsvetkov, Dmitry1 (AUTHOR), Zuev, Andrey1 (AUTHOR)
Source: Journal of Alloys & Compounds. Dec2020, Vol. 845, pN.PAG-N.PAG. 1p.
Subjects: Composite materials, Crystal lattices, Perovskite, Electric conductivity, Methane hydrates, Water, Case studies
Abstract: Some layered double perovskite cobaltites have been shown recently to absorb water and exhibit increasing electrical conductivity in humid atmospheres. However, the assumptions that their crystal lattice is capable of proton uptake, and that these oxides really possess triple (oxide ion, protonic and electronic) conductivity, have already been brought into question. We investigated in detail the crystal structure and phase composition of various lanthanum-substituted GdBaCo 2 O 6−δ and came to several important conclusions. Firstly, in oxidative conditions (e.g. in air), the substitution of La for either only Gd or only Ba in GdBaCo 2 O 6−δ results in formation of multiphase materials. For example, BaCo 1– x Gd x O 3−δ exsolves from Gd 1– x La x BaCo 2 O 6−δ due to the redistribution of La between Gd and Ba sites in Gd 1– x La x BaCo 2 O 6−δ lattice. Secondly, a single-phase double perovskite can be synthesized in air only by simultaneously substituting, within certain limits, both Gd and Ba in GdBaCo 2 O 6−δ with La. Finally, using Gd 0.8 La 0.2 Ba 0.95 La 0.05 Co 2 O 6−δ and BaCo 0.8 Gd 0.2 O 3−δ as examples, we demonstrated that while single-phase double perovskite does not hydrate, in the same conditions, the cubic perovskite BaCo 0.8 Gd 0.2 O 3−δ (BaCo 1– x Gd x O 3−δ is encountered in Gd 1– x La x BaCo 2 O 6−δ as an impurity) absorbs significant amount of water. Thus, the water uptake by lanthanum-substituted GdBaCo 2 O 6−δ is most likely to occur due to the impurities, and not the main double perovskite phase. • Substitution of La for only Gd or only Ba in GdBaCo 2 O 6−δ yields multiphase materials. • Single-phase simultaneously substituted Gd 1– x La x Ba 1– y La y Co 2 O 6−δ can be synthesized. • Water uptake by Gd 1– x La x BaCo 2 O 6−δ is most likely due to impurities. [ABSTRACT FROM AUTHOR]
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Abstract:Some layered double perovskite cobaltites have been shown recently to absorb water and exhibit increasing electrical conductivity in humid atmospheres. However, the assumptions that their crystal lattice is capable of proton uptake, and that these oxides really possess triple (oxide ion, protonic and electronic) conductivity, have already been brought into question. We investigated in detail the crystal structure and phase composition of various lanthanum-substituted GdBaCo 2 O 6−δ and came to several important conclusions. Firstly, in oxidative conditions (e.g. in air), the substitution of La for either only Gd or only Ba in GdBaCo 2 O 6−δ results in formation of multiphase materials. For example, BaCo 1– x Gd x O 3−δ exsolves from Gd 1– x La x BaCo 2 O 6−δ due to the redistribution of La between Gd and Ba sites in Gd 1– x La x BaCo 2 O 6−δ lattice. Secondly, a single-phase double perovskite can be synthesized in air only by simultaneously substituting, within certain limits, both Gd and Ba in GdBaCo 2 O 6−δ with La. Finally, using Gd 0.8 La 0.2 Ba 0.95 La 0.05 Co 2 O 6−δ and BaCo 0.8 Gd 0.2 O 3−δ as examples, we demonstrated that while single-phase double perovskite does not hydrate, in the same conditions, the cubic perovskite BaCo 0.8 Gd 0.2 O 3−δ (BaCo 1– x Gd x O 3−δ is encountered in Gd 1– x La x BaCo 2 O 6−δ as an impurity) absorbs significant amount of water. Thus, the water uptake by lanthanum-substituted GdBaCo 2 O 6−δ is most likely to occur due to the impurities, and not the main double perovskite phase. • Substitution of La for only Gd or only Ba in GdBaCo 2 O 6−δ yields multiphase materials. • Single-phase simultaneously substituted Gd 1– x La x Ba 1– y La y Co 2 O 6−δ can be synthesized. • Water uptake by Gd 1– x La x BaCo 2 O 6−δ is most likely due to impurities. [ABSTRACT FROM AUTHOR]
ISSN:09258388
DOI:10.1016/j.jallcom.2020.156309