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Variable-Temperature Mössbauer Spectroscopy of Nano-Sized Maghemite and Al-Substituted Maghemites

Published online by Cambridge University Press:  28 February 2024

G. M. Da Costa ,
E. De Grave ,
L. H. Bowen ,
P. M. A. De Barker  and
R. E. Vandenberghe
G. M. Da Costa
Affiliation:
Laboratory of Magnetism, Department of Subatomic and Radiation Physics University of Gent, B-9000 Gent, Belgium On leave from Departamento de Química, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil
E. De Grave*
Affiliation:
Laboratory of Magnetism, Department of Subatomic and Radiation Physics University of Gent, B-9000 Gent, Belgium
L. H. Bowen
Affiliation:
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204
P. M. A. De Barker
Affiliation:
Laboratory of Magnetism, Department of Subatomic and Radiation Physics University of Gent, B-9000 Gent, Belgium
R. E. Vandenberghe
Affiliation:
Laboratory of Magnetism, Department of Subatomic and Radiation Physics University of Gent, B-9000 Gent, Belgium
*
*Research Director, National Fund for Scientific Research, Belgium.
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Abstract

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Synthetic aluminum-substituted maghemite samples, γ-(Fe1-xAlx)2O3, have been prepared by thermal decomposition of Al-lepidocrocite (γ-Fe1-xAlxOOH), with × = 0, 0.04, 0.06, 0.14 and 0.18. The particles are needle-shaped and the mean crystallite diameter along the [311] crystallographic direction was found to be between 2.0 and 5.0 nm. Mössbauer spectra were collected at 6 K and from 80 K up to 475 K at steps of 25 K. In a wide range of temperatures the spectra of the non-substituted sample consist of a superposition of a broad sextet and a superparamagnetic doublet, whereas for the Al-maghemites this range is much smaller. From the temperature variation of the fractional doublet area two different parameters were defined: the temperature corresponding to a 50/50 doublet-sextet spectrum (T1/2), and the temperature below which the doublet ceases to exist (T0). These two parameters (T1/2 and T0) decrease from 390 K and 92 K (Al-free sample), to 118 K and 64 K (4 mole % Al) and to 100 K and 48 K (18 mole % Al), respectively. The average hyperfine fields at 6 K undergo a steep drop in going from the Al-free sample (Hhf = 506 kOe) to the sample with 4 mole % Al (Hhf = 498 kOe), but for higher substitutions the effect is much smaller. The A- and B-site quadrupole splittings, obtained from the data between 220 K and 475 K, were found as: ΔEQ,A = 0.86 ± 0.04 mm/s and ΔEQ,B = 0.65 ± 0.04 mm/s for the 4 mole % Al sample. The characteristic Mössbauer temperature, determined from the temperature dependence of the average isomer shift, was found to be in the range of 500–600 K.

Keywords

Al substitutionMaghemiteMössbauer effect
Type
Research Article
Information
Clays and Clay Minerals , Volume 43 , Issue 5 , October 1995 , pp. 562 - 568
Copyright
Copyright © 1995, The Clay Minerals Society

References

Bowen, L. H., Grave, E. De, and Bryan, A. M. 1994. Mössbauer studies in external field of well crystallized Al-maghemites made from hematite. Hyperfine Interactions 94: 1977–1982.Google Scholar
Bryan, A. M., 1993. The thermal transformation of Al-sub-stituted hematite and lepidocrocite to maghemite studied by 57Fe Mössbauer spectroscopy. Ph.D. thesis. North Carolina State University, USA.Google Scholar
da Costa, G. M., Grave, E. De, Bryan, A. M., and Bowen, L. H. 1994a. Mössbauer studies of nano-sized aluminum-substituted maghemites. Hyperfine Interactions 94: 1983–1988.Google Scholar
da Costa, G. M., Grave, E. De, Bowen, L. H., de Bakker, P. M. A., and Vandenberghe, R. E. 1994b. Temperature dependence of the hyperfine parameters of maghemite and Al-substituted maghemites. Phys. Chem. Minerals 22: 178–185.Google Scholar
da Costa, G. M., Grave, E. De, Bowen, L. H., de Bakker, P. M. A., and Vandenberghe, R. E. 1994c. The center shift in Mössbauer spectra of Maghemite and Aluminum maghemites. Clays & Clay Miner. 42: 628–633.Google Scholar
de Bakker, P. M. A., Grave, E. De, Vandenberghe, R. E., Bowen, L. H., Pollard, R. J., and Persoons, R. M. 1991. Mössbauer study of the thermal decomposition of lepidocrocite and characterisation of the decomposition products. Phys. Chem. Minerals 18: 131–143.Google Scholar
De Grave, E., and Alboom, A. Van. 1991. Evaluation of ferrous and ferric Mössbauer fractions. Phys. Chem. Minerals 18: 337–342.Google Scholar
Gillot, B., and Rousset, A. 1990. On the limit of aluminum substitution in Fe3O4 and γ-Fe2O3. Phys. Status Solidi (a) 118: K5–K8.Google Scholar
Haneda, K., and Morrish, A. H. 1977. Vacancy ordering in γ-Fe2O3 small particles. Solid State Comm. 22: 779–782.Google Scholar
Hendriksen, P. V., Oxborrow, C. A., Linderoth, S., Mørup, S., Hanson, M., Johansson, C., Bødker, F., Davies, K., Charles, S. W., and Wells, S. 1993. Particle interaction effects in systems of ultrafine iron oxide particles. Nucl. Inst. Meth. Phys. Res. B76: 138–139.Google Scholar
Koch, J. W. C., Madsen, M. B., and Mørup, S. 1986. Decoupling of magnetically interacting crystallites of goethite. Hyperfine Interactions 28: 549–552.Google Scholar
Le Caer, G., Dubois, J. M., Fischer, H., Gonser, U., and Wagner, H. G. 1984. On the validity of “Fe hyperfine field distribution calculation from Mössbauer spectra of magnetic amorphous alloys. Nucl. Instr. Methods B5: 25–33.Google Scholar
Mørup, S., and Topsøe, H. 1976. Mössbauer studies of thermal excitation in magnetically ordered microcrystals. Appl. Phys. 11: 63–66.Google Scholar
Prené, P., Tronc, E., Jolivet, J. P., Livage, J., Cherkaoui, R., Nogues, M., Dormann, J. L., and Fiorani, D. 1993. Magnetic properties of isolated γ-Fe2O3 particles. IEEE Trans. Magn. 29: 2658–2660.Google Scholar
Schwertmann, U., 1988. Some properties of soil and synthetic iron oxides. In Iron in Soils and Clay Minerals, Stucki, J. W., Goodman, B. A., and Schwertmann, U., eds. Dordrecht: Reidel, pp. 203–250.Google Scholar
Van der Kraan, A. M., 1973. Mössbauer effect studies of surface ions of ultrafine α-Fe2O3 particles. Phys. Status Solidi (a) 18: 215–226.Google Scholar
Vandenberghe, R. E., and Grave, E. De. 1989. Mössbauer studies of oxidic spinels. In Mössbauer Spectroscopy Applied to Inorganic Chemistry. Long, G. J., and eds, F. Grandjean. Vol 3, New York: Plenum Press, pp 59–182.Google Scholar
Wolska, E., and Schwertmann, U. 1989. The vacancy ordering and distribution of aluminium ions in γ-(Fe,Al)2O3. Solid State Ionics 32/33: 214–218.Google Scholar