Browsing by Author "Schnellrath, Jurgen"

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    Rockbridgeite inclusion in rock crystal from Galileia region, Minas Gerais, Brazil.
    (2013) Faulstich, Fabiano Richard Leite; Schnellrath, Jurgen; Oliveira, Luiz F. C. de; Cipriano, Ricardo Augusto Scholz
    A set of rock crystals with pleochroic inclusions were analyzed by optical microscopy, scanning electron microscopy, Raman spectroscopy and energy-dispersive spectrometry (EDS). The inclusions occur in fracture planes, have a discoid form with radial and concentric structure, diameters ranging from a few micrometers to several millimeters and thicknesses smaller than 50 mm. They have a pronounced pleochroism ranging from yellow to green when fresh and a brown color when oxidized. The Raman spectrum of the inclusion is characterized by a set of bands associated to the n1 and n3 PO4 tetrahedra stretching region (at 1186, 1137, 1061, 981 and 937 cm 1), overlapping bands associated to the n2 and n4 bending phosphate tetrahedra (at 638, 616, 576 and 463 cm 1), a suite of overlapping vibrations of XO6 octahedra (382, 333, 299 and 241 cm 1), a broad band between 3000 and 3500 cm 1 associated to the OH stretching vibration of molecular water and a sharp band at 3575 cm 1 corresponding to the stretching vibrations of OH groups. The spectrum and compositional data indicating iron, manganese and phosphorous as the main elements point to rockbridgeite, with the empirical formula (Fe2þ, Mn2þ)Fe3þ 4(PO4)3(OH)5 and an Fe2þ:Mn2þ ratio close to 1.
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    Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite.
    (2010) 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
    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.