Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite.

Dias, Lorena Nunes; Pinheiro, Mauricio Veloso Brant; Moreira, Roberto Luiz; Krambrock, Klaus Wilhelm Heinrich; Guedes, Kassílio José; Menezes Filho, Luiz Alberto Dias; Karfunkel, Joachim; Schnellrath, Jurgen; Cipriano, Ricardo Augusto Scholz

Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite.

Date

2010

Authors

Dias, Lorena Nunes

Pinheiro, Mauricio Veloso Brant

Moreira, Roberto Luiz

Krambrock, Klaus Wilhelm Heinrich

Guedes, Kassílio José

Menezes Filho, Luiz Alberto Dias

Karfunkel, Joachim

Schnellrath, Jurgen

Cipriano, Ricardo Augusto Scholz

Abstract

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.

Keywords

Montebrasite, Amblygonite, Niobyl

Citation

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.