Mixed-Valence Iron Dumortierite Fe13.52.22+(As5+O4- x)8(OH)6 and Its Intricate Topotactic Exsolution at Mild Temperatures

Synthesis, structure and magnetic behavior of iron arsenites with hierarchical magnetic units

Iron-arsenites may cover multiple Fe oxidation states, while the versatile (AsO₃)²⁻ condensation offer ideal spacers between magnetic sub-units with various dimensionalities (D). We show here four novel compounds covering the 0–3D magnetic panorama.

The hidden story in BaNiO3 to BaNiO2 transformation: adaptive structural series and NiO exsolution

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.