Vacancy ordering in γ-Fe2O3 small particles

Haneda, K.; Morrish, A. H.

doi:10.1016/0038-1098(77)90067-9

Cited by 142 publications

(57 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…All observed peaks can be assigned to the spinel phase. Some superstructure lines are clearly visible, indicating an ordered arrangement of the vacancies on the B sites (Haneda and Morrish, 1977). The diffractograms for the other samples all resemble those shown in Figure 1.…”

Section: Methodssupporting

confidence: 61%

“…It is commonly represented by the formula (Fe) However, some authors also report the vacancies to enter both octahedral and tetrahedral sites simultaneously (Armstrong et al, 1966;Annersten and Hafner, 1973;Haneda and Morrish, 1977). Besides its technological importance as a material for recording devices, maghemite is of considerable geophysical interest since it occurs in many tropical magnetic soils (Schwertmann and Fechter, 1984;Fontes and Weed, 1991) and is believed to be a significant constituent of the Martian surface (Coey et aL, 1990).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites

Costa

1994

Clays and clay miner.

View full text Add to dashboard Cite

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.

show abstract

Section: Methodssupporting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites

Costa

1994

Clays and clay miner.

View full text Add to dashboard Cite

show abstract

“…It can be represented by the formula Fe 34 [Fe345/3 [~/3104, where again the brackets represent octahedral sites. The vacancies ([2) are also reported to occur in both sites simultaneously (Armstrong et al 1966;Annersten and Hafner 1977;Haneda and Morrish 1977). The zero-field room temperature Mtssbauer spectrum is composed of two sextets, but their hyperfine parameters are so close to one another that they can only be distinguished by numerical deconvolution.…”

Section: Introductionmentioning

confidence: 99%

Influence of Nonstoichiometry and the Presence of Maghemite on the Mössbauer Spectrum of Magnetite

Costa

1995

Clays and clay miner.

View full text Add to dashboard Cite

Abstract--Several samples of large-and small-particle magnetite (Fe304), as well as its thermal decomposition products formed at different temperatures and atmospheres, have been studied extensively by Mrssbauer spectroscopy (MS), both with and without an applied field of 6T. Synthetic mixtures of magnetite and poorly-or well-crystallized maghemite have also been studied. Large-particle magnetite (MCD > 200 nm), when heated in air for 12 hours at T < 400*(2, transforms to a mixture of wellcrystallized hematite and magnetite, the latter one remaining stoichiometric, according to the relative area-ratios obtained from MS. Thermal treatment at 1300"C in a controlled 02 partial pressure, produced a mixture of stoichiometric and nonstoichiometric magnetite, but the latter component seems to be composed of particles with different degrees of nonstoichiometry. The Mrssbauer spectra of the decomposition products at T < 200"C in air of small-particle magnetite (MCD ~ 80 nm) could be successfully interpreted as a mixture of magnetite and maghemite, rather than nonstoichiometric magnetite. This suggestion is further supported by the experiments with the synthetic mixtures. It is clearly demonstrated that is not possible, even by applying a strong external field, to separate the contribution of the A-site of magnetite from that of maghemite.

show abstract

“…Перспективным [14] и ссылки там), тем не менее, их аномальные магнитные свойства, такие как пониженная намагниченность насыщения, по сравнению с объем-ными величинами, обменное смещение в однофазных наночастицах и высокополевые восприимчивости все еще плохо изучены и обычно приписываются скосу спи-новой структуры или дефектам на внешней поверхности частиц [19,20]. Отсюда следует, что необходимы иссле-дования, связывающие структурные особенности (напри-мер, дефекты) внутри магнитных наночастиц (МНЧ) с наблюдаемыми аномальными магнитными свойствами.…”

Section: Introductionunclassified