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The hidden story in BaNiO3 to BaNiO2 transformation: adaptive structural series and NiO exsolution
Angel M Arévalo-López1, Marielle Huvé, Pardis Simon
1Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 - UCCS - Unité de Catalyse et Chimie du Solide, F-59000 Lille, France. olivier.mentre@ensc-lille.fr.
Abstract:
BaNiO3 crystal to BaNiO2 crystal transformation is reported. Contrary to an intuitive topochemical reduction, a two step reaction was observed. In the first step, NiO exsolution occurs and intermediate Ba1+xNiO3 phases were obtained and isolated. A composite approach was used to solve the novel structure for x ∼ 1/6 with charge ordered Ni2+ and Ni4+. We argue that this NiO exsolution is responsible for the increased oxygen enhanced reactivity recently reported. Upon re-oxidation, oxygen-deficient mixed valent BaNi3/4+O3-x are obtained such that the full redox cycle is irreversible and goes through a diversity of structural and nickel valence adaptative oxides.
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