Issue 0, 1975

Mössbauer studies in the colloid system β-FeOOH–β-Fe2O3: structures and dehydration mechanism

Abstract

The Mössbauer spectrum of the recently reported β-iron(III) oxide has been measured and that of β-iron(III) oxide hydroxide re-investigated. The Néel temperature of β-iron(III) oxide lies between 300 and 380 K and the average magnetic field at 4.2 K is 49.5 tesla. Magnetic relaxation effects are observed. The spectrum above the Néel temperature is a broad asymmetric doublet, consisting of peaks having a continuous distribution of velocities, with the most probable quadrupole splitting occurring at 1.0 mm s–1, and the most probable isomer shift, extrapolated to 295 K, occurring at 0.31 mm s–1. While the distribution is within the known range of parameters of 6 or 5 co-ordinated Fe3+ in oxides, a proportion of tetrahedral Fe3+, with a lower isomer shift, could also exist within the broad spectral envelope, and a possible concentration range of from 0 to 40 % was estimated.

The spectrum of β-iron(III) oxide hydroxide is consistent with octahedral Fe3+. The high proportion of ions on the internal surfaces of the tubular structure results in a non-stoichiometric surface anion excess, and the conventional formula β-FeOOH has been reformulated as β-FeOx(OH)3–2x, where x≈ 0.9.

Four models of the anion vacancy distribution in β-iron(III) oxide are considered within the framework of the tubular structure retained during dehydration, and a defect structure is proposed which is consistent with the Mössbauer, X-ray, magnetic and B.E.T. data: all the internal Fe3+ ions are 5 co-ordinated whilst the surface Fe3+ ions are tetrahedrally co-ordinated.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans. 1, 1975,71, 22-34

Mössbauer studies in the colloid system β-FeOOH–β-Fe2O3: structures and dehydration mechanism

A. T. Howe and K. J. Gallagher, J. Chem. Soc., Faraday Trans. 1, 1975, 71, 22 DOI: 10.1039/F19757100022

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