Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

Albrecht R, Hunger J, Block T, Poettgen R, Senyshyn A, Doert T, Ruck M (2019)

Publication Type: Journal article

Publication year: 2019

Journal

ChemistryOpen Wiley Open Access: Chemistry Open / Wiley

Book Volume: 8

Pages Range: 74-83

Journal Issue: 1

DOI: 10.1002/open.201800229

Abstract

The reaction of Fe(NO3)3⋅9 H2O with KOH under hydroflux conditions at about 200 °C produces red crystals of K2−xFe4O7−x(OH)x in a quantitative yield. In the crystal structure, edge-sharing [FeO6] octahedra form ∞ 2[Fe2O6] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO4] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P (Formula presented.) 1m) and the hexagonal (P63/mcm) polytypes of K2−xFe4O7−x(OH)x show oriented intergrowth. The sub-stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K2−xFe4O7−x(OH)x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K2−xFe4O7−x(OH)x hydrolyzes and K2CO3 ⋅ H2O forms gradually on the surface of the K2−xFe4O7−x(OH)x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K2−xFe4O7−x(OH)x proceeds via a topotactic transformation into K1+x′Fe11O17, adopting the rhombohedral β’’ or the hexagonal β-aluminate-type structure, before γ-Fe2O3 is formed above 950 °C, which then converts into thermodynamically stable α-Fe2O3.

Involved external institutions

Westfälische Wilhelms-Universität (WWU) Münster DE Germany (DE) Technische Universität München (TUM) DE Germany (DE) Technische Universität Dresden DE Germany (DE)

How to cite

APA:

Albrecht, R., Hunger, J., Block, T., Poettgen, R., Senyshyn, A., Doert, T., & Ruck, M. (2019). Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures. ChemistryOpen, 8(1), 74-83. https://doi.org/10.1002/open.201800229

MLA:

Albrecht, Ralf, et al. "Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures." ChemistryOpen 8.1 (2019): 74-83.

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