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  • 1
    Electronic Resource
    Electronic Resource
    The electronic structure of ilvaite and the pressure and temperature dependence of its ^5^7Fe Mossbauer spectrum
    Amsterdam : Elsevier
    Journal of Physics and Chemistry of Solids 41 (1980), S. 985-1001 
    Details
    ISSN: 0022-3697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-3697(80)90106-7
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  • 2
    Electronic Resource
    Electronic Resource
    Fe^3^+ in shocked olivine crystals of the ALHA 77005 meteorite
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 67 (1984), S. 162-166 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0012-821X(84)90111-0
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of Mn-bearing ilvaite CaFe 2−x 2+ MnxFe3+ [Si2O7/O/(OH)] (1989)
    Springer
    Mineralogy and petrology 40 (1989), S. 101-109 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Mn-haltiger Ilvait CaFe 2−x 2+ Mnx Fe3+ [Si2O7/O/(OH)] wurde unter hydrothermalen Bedingungen bei Drucken von 2 und 3 kbar, Temperaturen zwischen 300 und 400°C und bei Sauerstoff Fugazitäten, die durch Festkörperpuffer (Fe2O3/Fe3O4 und Ni/NiO) kontrolliert wurden, hergestellt. Röntgenbeugungsuntersuchungen zeigen, daß mit steigendem Mn-Einbau der monokline Winkelβ kleiner wird, und daß bei x = 0.19 ein Phasenübergang von der monoklinen zur orthorhombischen Struktur erfolgt. Die Fe-Verteilung wurde mit Mössbauer-Spektroskopie bestimmt.
    Notes: Summary Synthesis of Mn-bearing ilvaites, CaFe 2−x 2+ MnxFe3+ [Si2O7/O/(OH)], with 0 ≤ x ≤0.19, have been performed under hydrothermal conditions at 2 and 3 kbars, T = 300 -400°C and at oxygen fugacities defined by the Fe2O3/Fe3O4 - and the Ni/NiO -buffer. As shown by X-ray diffraction, the substitution of Fe2+ by Mn2+ decreases the monoclinic angleβ and causes a phase transition from monoclinic to orthorhombic at x = 0.19. The Fe-distribution has been determined by Mössbauer spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01164320
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  • 4
    Electronic Resource
    Electronic Resource
    The role of Fe2+ and Fe3+ in synthetic Fe-substituted tetrahedrite (1990)
    Springer
    Mineralogy and petrology 43 (1990), S. 73-81 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Die Rolle von Fe2+ und Fe3+ in synthetischen Tetraedriten mit Fe-Substitution Tetraedrite mit einer Zusammensetzung zwischen Cu12Sb4S13 and Cu10Fe2Sb4S13 wurden bei 457 °C und 500 °C aus den Elementen synthetisiert und sorgfdltig mit Mössbauer-Spektroskopie von57Fe untersucht. Zwischen Cu12Sb4S13 and Cu11Fe1Sb4S13 ist Eisen überwiegend dreiwertig. Zwischen Cu11Fe1Sb4S13 and Cu11Fe2Sb4S13 ist Eisen überwiegend zweiwertig und besetzt die tetraedrisch koordinierten M1-Plätze.
    Notes: Summary Tetrahedrites with the composition between Cu12Sb4S13 and Cu10Fe2Sb4S13 were synthesized at 457 °C and 500 °C from the elements and carefully studied by Mössbauer spectroscopy of57Fe. Between Cu12Sb4S13 and Cu11Fe1Sb4S13 iron is predominantly ferric. Between Cu11Fe1Sb4S13 and Cu10Fe2Sb4S13 iron is predominantly ferrous and occupies the tetrahedral M1-sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01164223
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  • 5
    Electronic Resource
    Electronic Resource
    Preface (1995)
    Springer
    Mineralogy and petrology 53 (1995), S. i 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01160147
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of themixed valent iron silicate ilvaite, CaFe3[Si2O7/O/(OH)] (1987)
    Springer
    Mineralogy and petrology 37 (1987), S. 97-108 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Das gemischt valente Eisensilikat Ilvait CaFe 2 2 +Fe3+ [Si2O7/0/(OH)] wurde unter hydrothermalen Bedingungen bei Temperaturen zwischen 300 und 500 °C, Drucken zwischen 1,5 und 4,0 Kbar und bei Sauerstoff-Fugazitäten, die durch Festkörperpuffer (Fe3O4/Fe2O3, Fe/Fe3O4 and Ni/NiO) kontrolliert wurden, hergestellt. Diese Ilvaite sind alle monoklin mit den Zellparameters a0=13,0065 (9) Å, b0 = 8,8073 (7) Å, c0 = 5,8580 (4) Å und β = 90,332 (6)°. Die Qualität der Proben wurde mit Mössbauer Spektroskopie überprüft. Rasterelektronenmikroskopische Aufnahmen zeigten idiomorphe Kristalle mit einer Größe bis 30 μ.
    Notes: Summary The mixed valent iron silicate ilvaite CaFe 2 2 +Fe3+ [Si2O7/O/(OH)] has been synthesized under hydrothermal conditions at temperatures between 300 and 500°C, pressures between 1.5 and 4 Kbars and oxygen fugacities controlled by the solid state buffers Fe3O4/Fe2O3, Fe/Fe3O4 and Ni/NiO. All these ilvaites are monoclinic (P21/a with cell parameters a0 = 13.0065 (9) Å, b0 = 8.8073 (7) Å, c0 = 5.8580 (4) Å, and β = 90.332 (6)°. The quality of the samples has been checked by Mössbauer spectroscopy. Scanning electron microscopic pictures show small euhedral crystals with a size up to 30 μ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01164185
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  • 7
    Electronic Resource
    Electronic Resource
    Electron delocalization in ilvaite, a reinterpretation of its 57Fe Mössbauer spectrum (1984)
    Springer
    Physics and chemistry of minerals 10 (1984), S. 250-255 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The Mössbauer spectra of ilvaite CaFe 2 2+ Fe3+[Si2O7/O/OH] and their temperature dependence between 298 K and 455 K can be satisfactorily least-squares fitted by a superposition of the resonances for Fe2+(8d), Fe3+(8d) and Fe2+(4c). The relative areas under the three resonances are nearly equal and vary only weakly with temperature. No additional resonances or line broadenings have to be introduced, if we assume that the hyperfine interactions of Fe2+(8d) and Fe3+(8d) fluctuate between their values due to electron hopping between the iron ions at the 8d sites. Hopping can be assumed to occur homogeneously among nearly equivalent sites. The fluctuation rate is described by an Arrhenius law with a pre-exponent of about 9 × 108 s−1 and an activation energy of 0.11 eV indicating non-adiabatic hopping. In addition to the intersite hopping process, the strong decrease of the quadrupole splitting and the isomer shift of Fe2+(8d) between 298 K and 360 K suggests the occurrence of intrinsic charge delocalization from Fe2+(8d) which does not involve the neighbouring Fe3+(8d) ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00311949
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  • 8
    Electronic Resource
    Electronic Resource
    Crystallographic phase transition and valence fluctuation in synthetic mn-bearing ilvaite CaFe2+ 2-x Mn2+ xFe3+ [Si2O7/O/(OH)] (1992)
    Springer
    Physics and chemistry of minerals 18 (1992), S. 491-496 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The dependence of the electronic and the crystallographic structure on temperature of synthetic Mnbearing ilvaites CaFe2+ 2-xMn2+ xFe3+ [Si2O7/O/OH] with 0≤x≤0.19 has been investigated. The change of the electronic structure was studied by 57Fe Mössbauer spectroscopy. The spectra show an increasing valence fluctuation rate between Fe2+ and Fe3+ in the double chain of edge-sharing octahedra with increasing temperature resulting in a mixed valent state of iron. The valence fluctuation rate is distinctly increased by the Mnsubstitution. The temperature of the crystallographic phase transition T x as studied by a high temperature Guinier method is distinctly lowered by the Mn-substitution (x = 0.0, T x=390K; x = 0.12, T x =370K; x = 0.19, T x=295K). The reasons for this behaviour are discussed in terms of Fe2 +, Fe3 + cation order-disorder, electronic relaxation rate, and relaxation of the lattice. In the monoclinic phase there is electron hopping between Fe2 +, Fe3 + pairs whereas in the orthorhombic phase there is extended electron delocalization via a narrow, d-band mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00205263
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic properties of the clinopyroxenes aegirine and hedenbergite: a magnetic susceptibility study on single crystals (1997)
    Springer
    Physics and chemistry of minerals 24 (1997), S. 294-300 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Two natural clinopyroxene single crystals were investigated, an aegirine-augite (AEG) and a magnesian hedenbergite (HED). Both samples were carefully characterized by electron microprobe, X-ray diffraction, and Mössbauer spectroscopy. Magnetic susceptibility measurements of powdered samples reveal low temperature antiferromagnetic coupling and Curie-Weiss behaviour with T N =7.5(5) K, Θ P =−19(1) K for AEG, and T N =31(1) K, Θ P =+21(1) K for HED, respectively. Low temperature Mössbauer spectra exhibit relaxation phenomena. Magnetic susceptibility measurements of the single crystals show the direction of the magnetic moments to be lying within the a/c plane for both samples: 50(±2)° from a and 57(±2)° from c in AEG, and 45(±2)° from a and 60(±2)° from c in HED, respectively. The antiferromagnetic interchain interaction competes with the ferromagnetic intrachain interaction in both pyroxenes. In the magnesian hedenbergite a field induced magnetic transition is found. Its dependence on temperature, magnetic field and crystallographic direction is investigated and described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050041
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  • 10
    Electronic Resource
    Electronic Resource
    Study of the electrical charge transport in ilvaite using impedance spectroscopy and thermopower data (1998)
    Springer
    Physics and chemistry of minerals 25 (1998), S. 522-533 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The electrical conduction in the mineral ilvaite was studied between ≈170 and 450 K. A natural ilvaite from Elba (Italy) was found to be semiconducting with a DC conductivity 1.8×10–3 (Ωcm)–1 at 300 K, measured parallel (∥) to the [001] direction; perpendicular (⊥) to [001] it was 1.4×10–5 (Ωcm)–1, i.e. the conductivity is highly anisotropic. The conduction is effected by a hopping charge transport between localized levels in the energy gap associated with activation energies E A =0.3–0.5 eV. It is concluded that impurities (Mg,Al,Mn) may play a decisive role in the charge hopping transport ∥ [001] that is basically governed by Fe2+-Fe3+ pairs on A-sites of the lattice as the source of electrons. Although the EA-values were similar for both measured directions, the sign of thermopower is different which points to different charge transfer mechanisms. The bulk DC conductivity σDC AC for measurements ∥ [001], obtained by extrapolation of AC data using impedance spectroscopy, could only be determined at T〈300 K owing to sample–electrode interfacial effects. In contrast, the bulk σDC AC⊥ [001] showed a slight break at ≈380 K that may reflect the structural phase transition monoclinic→orthorhombic at ≈345 K. From AC conductivity measurements in the frequency range 20 Hz–1 MHz at T〈300 K, a dispersive character of electronic relaxation was found, resembling that of amorphous semiconductors and of impurity conduction in crystalline semiconductors where it was ascribed to charge hopping processes of electrons between localized levels of cation pairs or clusters of limited lengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050144
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