Mössbauer study of the thermal decomposition of lepidocrocite and characterization of the decomposition products

Bakker, P. M. A. de; Grave, E. De; Vandenberghe, R. E.; Bowen, L. H.; Pollard, R. J.; Persoons, Rosita

doi:10.1007/bf00216606

Cited by 44 publications

(32 citation statements)

References 44 publications

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“…At 4.2 K values as high as 0.48 mm/s for ~A and 0.62 for bB have been reported (Pollard, 1988;Pollard and Morrish, 1987;Collyer et al, 1988;Mehner et al, 1990;de Bakker et al, 1991;Nikumbh et aL, 1992). In an attempt to resolve this discrepancy, variable-temperature Mrssbauer spectra (MS) between 8 K and 475 K, and in addition at 4.2 K and 275 K with the absorber subjected to an external field of 60 kOe, were collected for a number of wellcrystallized maghemite and Al-maghemite samples.…”

Section: Introductionmentioning

confidence: 86%

“…Commonly occurring effects such as small-particle size distributions and partial substitution of the iron atom by another cation tend to cause line broadening and/or a line-shape asymmetry, and in many cases the RT spectrum has to be fit with a distribution of unresolved A-and B-site hyperfine fields Copyright 9 1994, The Clay Minerals Society (de Bakker et aL, 1991). On lowering the temperature it is possible, depending on the crystallinity, to obtain a somewhat better resolution of the two sites, but the only way to have them sufficiently separated is by applying strong external magnetic fields (Armstrong et al, 1966).…”

Section: Introductionmentioning

confidence: 99%

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The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites

Costa

1994

Clays and clay miner.

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Abstract--Synthetic, relatively well-crystallized aluminum-substituted maghemite samples, y-(Aly. Fe~_y)203, with y = 0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by X-ray diffraction and zero-field Mrssbauer spectroscopy in the range 8 K to 475 K, and also with an external field of 60 kOe at 4.2 K and 275 K. It was found that there are two different converging models for fitting the zero-field spectra of the maghemites with a superposition of two Lorentzian-shaped sextets, both resulting in inconsistent values for the hyperfine fields (Hhf) and/or the center shifts (6) of the tetrahedral (A) and octahedral (B) ferric ions. From the applied-field measurements it is concluded that there is a constant difference of 0.12 _+ 0.01 mm/s between 6B and 6A, regardless of the A1 content.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites

Costa

1994

Clays and clay miner.

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“…The ubiquity of its explanation originates in an inability to distinguish between the surface and finite-size effects in a nanoparticle system as their influences are, in most cases, mixed together. In addition, it is also not clear, if spin canting anomaly in maghemite nanoparticles is peculiar only to the octahedral sites with cation vacancies [64] or if it is the same for both sites conserving thus the antiparallel orientation of the A-site and B-site magnetic moments with respect to each other [79].…”

Section: O N C L U S I O Nmentioning

confidence: 98%

Zero-field and in-field Mössbauer spectroscopy as a tool for structural and magnetic characterization of maghemite (γ-Fe2O3) nanoparticles

Zbořil

2005

Czech J Phys

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“…Our XRD data for nearly pure maghemites LPS2-3-265 and LPS2-300-223 ( heating period (discussed below), it is not possible to correlate results with heating temperature. However, our hematites, like those of de Bakker et al (1991), are well ordered compared to their maghemite precursor.…”

Section: Figmentioning

confidence: 79%

“…Gehring and Hofmeister (1 994), using heating periods of 0.5 h, report dehydroxylation in the interval 175-300 "C for their bulk susceptibility data. The thermogravimetric data of Lauer (1981) for LPS2 andde Bakker et al (1991) for lepidocrocite L86 show dehydroxylation (measured as weight loss) in the interval -190-240 "C (heating rate of 30 "C/h) and -200-275 "C (heating rate of 120 "C/h), respectively.…”

Section: Magnetic Propertiesmentioning

confidence: 99%

Lepidocrocite to maghemite to hematite: A pathway to magnetic and hematitic Martian soil

Morris

Golden²,

Shelfer³

et al. 1998

Meteorit & Planetary Scien

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Abstract-We examined decomposition products of lepidocrocite, which were produced by heating the phase in air at temperatures up to 525 "C for 3 and 300 h, by x-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic methods, and reflectance spectroscopy (visible and near-infkared (IR)). Singlecrystal lepidocrocite particles dehydroxylated to polycrystalline particles of disordered maghemite that subsequently transformed to polycrystalline particles of hematite. Essentially pure maghemite was obtained at 265 and 223 "C for the 3 and 300 h heating experiments, respectively. Its saturation magnetization (J,) and mass specific susceptibility are -50 Am2/kg and -400 x lo4 m3/kg, respectively. Because hematite is spectrally dominant, spectrally hematitic samples (ie., a minimum near 860 nm and a maximum near 750 nm) also could be strongly magnetic (J, up to -30 Am2/kg) from the masked maghemite component. Analyses by TEM showed that individual particles are polycrystalline with respect to both maghemite and hematite. The spectrally hematitic and magnetic Mh + Hm particles can satisfy the spectral and magnetic constraints for Martian surface materials over a wide range of values of Mh/(Mh + Hm) either as pure oxide powders or (within limits) as components of multiphase particles. These experiments are consistent with lepidocrocite as the precursor of Mh + Hm assemblages on Mars, but other phases (e.g., magnetite) that decompose to Mh and Hm are also possible precursors. Simulations done with a copy of the Mars Path$nder magnet array showed that spectrally hematitic Mh + Hm powders having Js equal to 20.6 Am2/kg adhered to all five magnets.

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Mössbauer study of the thermal decomposition of lepidocrocite and characterization of the decomposition products

Cited by 44 publications

References 44 publications

The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites

The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites

Zero-field and in-field Mössbauer spectroscopy as a tool for structural and magnetic characterization of maghemite (γ-Fe2O3) nanoparticles

Lepidocrocite to maghemite to hematite: A pathway to magnetic and hematitic Martian soil

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