57Fe Mössbauer effect study of Al-substituted lepidocrocites.
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1996
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Seven A|-containing lepidocrocite samples, ~/-Fe,_xAlxOOH, prepared from FeC12/AI(NO3)3
solutions with initial A1/(A1 + Fe) mole ratios C~ of 0.0025, 0.01, 0.025, 0.05, 0.075, 0.10 and 0.15 tool/
mol, were examined by means of M6ssbauer spectroscopy at room temperature (RT) and at various
temperatures in the range of 8 to 80 K. The spectra at RT and 80~ consist of broadened quadrupole
doublets and were analyzed in terms of a single doublet and of a model-independent quadrupole-splitting
distribution, the latter yielding the best fit. The observed variations of the quadrupole-splitting parameters
with increasing C i are inconclusive as to whether the A1 cations are substituting into the structure. The
temperature at which the onset of magnetic ordering is reflected in the spectra, was measured by the
therrnoscan method with zero source velocity. A gradual shift from 50 K for Ci = 0.0025 mol/mol to 44
K for Ci = 0.10 mol/mol was observed for that temperature. As compared to earlier studies of Al-free
~-FeOOH samples with similar morphological characteristics, the fractional doublet area in the mixed
sextet-doublet spectra at 35 K is significantly higher for the present lepidocrocites. This observation is
ascribed to the substitution of A1 cations into the lepidocrocite structure. A similar conclusion is inferred
from the variation with C~ of the maximum-probability hyperfine field derived from the spectra recorded
at 8 K and fitted with a model-independent hyperfine-field distribution. The magnetic results suggest that
for the sample corresponding to Ci = 0.15 mol/mol, not all of the initially present A1 has been incorporated
into the structure.
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A1 Substitution, Lepidocrocite, Mossbauer Spectra
Citação
DE GRAVE, E. et al. 57Fe Mössbauer effect study of Al-substituted lepidocrocites. Clays & Clay Minerals, v. 44, p. 214-219, 1996. Disponível em: <https://link.springer.com/article/10.1346/CCMN.1996.0440206>. Acesso em: 20 abr. 2017.