Hostname: page-component-586b7cd67f-dlnhk Total loading time: 0 Render date: 2024-11-30T17:02:11.168Z Has data issue: false hasContentIssue false
  • English
  • Français

Intervalence Electron Transfer and Magnetic Exchange in Reduced Nontronite

Published online by Cambridge University Press:  02 April 2024

Paul R. Lear  and
Joseph W. Stucki
Paul R. Lear
Affiliation:
Department of Agronomy, University of Illinois, Urbana, Illinois 61801
Joseph W. Stucki
Affiliation:
Department of Agronomy, University of Illinois, Urbana, Illinois 61801
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The effects of chemical reduction of structural Fe3+ in nontronite SWa-1 (ferruginous smectite) on intervalence electron transfer (IT) and magnetic exchange were investigated. Visible absorption spectra in the region 800-400 nm of a chemical reduction series of the SWa-1 nontronite revealed an IT band near 730 nm (13,700 cm−1). Both the intensity and position of this band were affected by the extent of Fe reduction. The intensity increased until the Fe2+ content approached 40% of the total Fe, then decreased slightly with more Fe2+. The position of the band also shifted to lower energy as the extent of reduction increased.

Variable-temperature magnetic susceptibility measurements showed that the magnetic exchange in unaltered nontronite is frustrated antiferromagnetic, but ferromagnetic in reduced samples. Magnetic ordering temperatures are in the range 10–50 K, depending on the extent of reduction. The ferromagnetic component in the magnetization curve increased with increasing Fe2+ in the crystal structure. The positive paramagnetic interaction likely is due to electron charge transfer from Fe2+ to Fe3+ through such structural linkages as Fe2+-O-Fe3+ (perhaps following a double exchange mechanism), which is consistent with the visible absorption spectra.

Keywords

Intervalence electron transferIronMagnetic susceptibilityNontroniteReductionUV-visible spectroscopy
Type
Research Article
Information
Clays and Clay Minerals , Volume 35 , Issue 5 , October 1987 , pp. 373 - 378
Copyright
Copyright © 1987, The Clay Minerals Society

References

Anderson, P. W., 1950 Antiferromagnetism. The theory of superexchange interaction Phys. Rev. 79 350 – 356.CrossRefGoogle Scholar
Anderson, P. W., 1959 New approach to the theory of superexchange interaction Phys. Rev. 115 2 – 13.CrossRefGoogle Scholar
Anderson, W. L., Stucki, J. W., Mortland, M. M. and Farmer, V. C., 1979 Effect of structural Fe2 on visible absorption spectra of nontronite suspensions Proc. Int. Clay Conf., Oxford, 1978 Amsterdam Elsevier 75 – 83.Google Scholar
Ballet, O. and Coey, J. M. D., 1982 Magnetic properties of sheet silicates; 2:1 layer minerals Phys. Chem. Miner. 8 218 – 229.CrossRefGoogle Scholar
Bonnin, D., 1981 Propriétés magnétiques liées aux désordres bidimensionnels dans un silicate lamellaire fer-rique: La nontronite .Google Scholar
Bonnin, D., Calas, G., Suquet, H. and Pezerat, H., 1985 Sites occupancy of Fe3+ in Garfield nontronite: A spectroscopic study Phys. Chem. Minerals 12 55 – 64.CrossRefGoogle Scholar
Coey, J. M. D. and Readman, P. W., 1973 Characterisation and magnetic properties of natural ferric gel Earth Planet. Sci. Letters 21 45 – 51.CrossRefGoogle Scholar
Goodenough, J. B., 1963 Magnetism and the Chemical Bond New York Interscience.Google Scholar
Goodman, B. A., Russell, J. D., Fraser, A. R. and Woodhams, F. W. D., 1976 A Mössbauer and I.R. spectroscopic study of the structure of nontronite Clays & Clay Minerals 24 53 – 59.CrossRefGoogle Scholar
Hush, N. S. and Cotton, F. A., 1967 Intervalence transfer absorption. Part 2. Theoretical considerations and spectroscopic data Progress in Inorganic Chemistry New York Interscience 357 – 390.Google Scholar
Kramers, H. A., 1934 L’interaction entre les atomes mag-nétogènes dans un cristal paramagnétique Physica 1 182 – 192.CrossRefGoogle Scholar
Lear, P. R. and Stucki, J. W., 1985 Role of structural hydrogen in the reduction and reoxidation of iron in nontronite Clays & Clay Minerals 33 539 – 545.CrossRefGoogle Scholar
Schatz, P. N. and Brown, D. B., 1980 A vibronic coupling model for mixed-valence compounds and its application to real systems Mixed-Valence Compounds Boston D. Reidel 115 – 188.CrossRefGoogle Scholar
Stucki, J. W., 1981 The quantitative assay of minerals for Fe2 and Fe3+ using 1,10-phenanthroline: II. A photochemical method Soil Sci. Soc. Amer. J. 45 638 – 641.CrossRefGoogle Scholar
Stucki, J. W., Stucki, J. W., Goodman, B. A., Schwertmann, U. and Dordrecht, D. R., 1987 Structural iron in smectites Iron in Soils and Clay Minerals 625 – 675.CrossRefGoogle Scholar
Stucki, J. W., Golden, D. C. and Roth, C. B., 1984 Effects of reduction and reoxidation of structural iron on the surface charge and the dissolution of dioctahedral smectites Clays & Clay Minerals 32 350 – 356.CrossRefGoogle Scholar
Zener, C., 1951 Interaction between the d shells in the transition metals Phys. Rev. 81 440 – 444.CrossRefGoogle Scholar