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Study of Al-substituted hematites, prepared from thermal treatment of lepidocrocite

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Abstract
A study of the characteristics of the Morin transition in aluminous hematites, alpha-(Fe1-xAlx)(2)O-3, produced from thermally transformed lepidocrocites, is reported. Six compositions with Al contents between 0.2 and 10 at% have been considered. It is argued that these samples present the advantage that they contain smaller amounts of hydroxyl and water as compared to hematites obtained by other preparation methods. The samples were characterised by a variety of conventional techniques, including thermal analyses, X-ray diffraction, FTIR, TEM/EDX, BET surface-area measurements and diffuse reflectance spectroscopy. All results indicate that the Al is structurally incorporated in the hematite lattices. Transmission Mossbauer spectra were recorded at various temperatures between 80 K and room temperature in order to precisely determine the Morin-transition region and the spin structure in both the low-temperature antiferromagnetic and weakly ferromagnetic states. It was found that the Morin-transition temperatures are markedly higher as compared to similar hematites made from aluminous goethites and that a transition phenomenon persists to an Al substitution of up to at least 10 at%. This different behaviour is ascribed to lower concentrations of structural hydroxyl groups in these lepidocrocite-based hematites.
Keywords
characterisation, hematite, Morin transition, Mossbauer spectroscopy, IRON-OXIDES, MORIN TRANSITION, MOSSBAUER, ALUMINUM, COLOR, TRANSFORMATION, SPECTROSCOPY, LIMITATIONS, PARAMETERS, CRYSTALS

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Chicago
Van San, Erwin, Eddy De Grave, Robert Vandenberghe, HO Desseyn, L Datas, V Barrón, and A Rousset. 2001. “Study of Al-substituted Hematites, Prepared from Thermal Treatment of Lepidocrocite.” Physics and Chemistry of Minerals 28 (7): 488–497.
APA
Van San, E., De Grave, E., Vandenberghe, R., Desseyn, H., Datas, L., Barrón, V., & Rousset, A. (2001). Study of Al-substituted hematites, prepared from thermal treatment of lepidocrocite. PHYSICS AND CHEMISTRY OF MINERALS, 28(7), 488–497.
Vancouver
1.
Van San E, De Grave E, Vandenberghe R, Desseyn H, Datas L, Barrón V, et al. Study of Al-substituted hematites, prepared from thermal treatment of lepidocrocite. PHYSICS AND CHEMISTRY OF MINERALS. 2001;28(7):488–97.
MLA
Van San, Erwin, Eddy De Grave, Robert Vandenberghe, et al. “Study of Al-substituted Hematites, Prepared from Thermal Treatment of Lepidocrocite.” PHYSICS AND CHEMISTRY OF MINERALS 28.7 (2001): 488–497. Print.
@article{169491,
  abstract     = {A study of the characteristics of the Morin transition in aluminous hematites, alpha-(Fe1-xAlx)(2)O-3, produced from thermally transformed lepidocrocites, is reported. Six compositions with Al contents between 0.2 and 10 at\% have been considered. It is argued that these samples present the advantage that they contain smaller amounts of hydroxyl and water as compared to hematites obtained by other preparation methods. The samples were characterised by a variety of conventional techniques, including thermal analyses, X-ray diffraction, FTIR, TEM/EDX, BET surface-area measurements and diffuse reflectance spectroscopy. All results indicate that the Al is structurally incorporated in the hematite lattices. Transmission Mossbauer spectra were recorded at various temperatures between 80 K and room temperature in order to precisely determine the Morin-transition region and the spin structure in both the low-temperature antiferromagnetic and weakly ferromagnetic states. It was found that the Morin-transition temperatures are markedly higher as compared to similar hematites made from aluminous goethites and that a transition phenomenon persists to an Al substitution of up to at least 10 at\%. This different behaviour is ascribed to lower concentrations of structural hydroxyl groups in these lepidocrocite-based hematites.},
  author       = {Van San, Erwin and De Grave, Eddy and Vandenberghe, Robert and Desseyn, HO and Datas, L and Barr{\'o}n, V and Rousset, A},
  issn         = {0342-1791},
  journal      = {PHYSICS AND CHEMISTRY OF MINERALS},
  keyword      = {characterisation,hematite,Morin transition,Mossbauer spectroscopy,IRON-OXIDES,MORIN TRANSITION,MOSSBAUER,ALUMINUM,COLOR,TRANSFORMATION,SPECTROSCOPY,LIMITATIONS,PARAMETERS,CRYSTALS},
  language     = {eng},
  number       = {7},
  pages        = {488--497},
  title        = {Study of Al-substituted hematites, prepared from thermal treatment of lepidocrocite},
  url          = {http://dx.doi.org/10.1007/s002690100169},
  volume       = {28},
  year         = {2001},
}

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