Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite.
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2010
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Natural single-crystal specimens of the montebrasite/amblygonite series from Brazil, with general
formula LiAlPO4(F,OH), were investigated by electron microprobe, Raman spectroscopy, X-ray diffraction,
and infrared absorption. Since little is known about impurities and their local symmetries,
electron paramagnetic resonance (EPR) was applied. Six different paramagnetic impurities and radiation
defects were detected by EPR. Three of them, all substituting for Al3+ ions, namely, iron (Fe3+),
vanadium (V4+), and niobium (Nb4+) impurities were characterized in this work. The Fe3+ (3d5)-related
EPR spectra and angular dependencies show occupation of low-symmetry sites that are revealed in
the high asymmetry parameter of the electronic fine structure, E/D = 0.27. Vanadium and niobium
impurities are identified through their typical strong hyperfine interactions. Both form interesting
examples for which the properties of 3d1 ion (V4+) and 4d1 ion (Nb4+) in the same host matrix can
be compared. It is shown that both ions form complex defects of type VO2+ (vanadyl) and NbO2+
(niobyl), showing superhyperfine interaction with two equivalent hydrogen ions and not to fluorine.
The EPR rotation patterns are analyzed in detail for three mutually perpendicular crystal planes. Spin
Hamiltonian parameters are calculated and discussed.
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Montebrasite, Amblygonite, Niobyl
Citação
DIAS, L. N. et al. Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite. The American Mineralogist, v. 96, p. 42-52, 2010. Disponível em: <https://rruff-2.geo.arizona.edu/uploads/AM96_42.pdf>. Acesso em: 20 de jun. 2017.