Optical absorption study of natural garnets of almandine-skiagite composition showing intervalence Fe2+ + Fe3+ -&gt; Fe3+ + Fe2+ charge-transfer transition

Taran, Michail N.; Dyar, M. D.; Matsyuk, S. S.

doi:10.2138/am.2007.2163

Cited by 25 publications

(34 citation statements)

References 14 publications

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“…The experimental spectra and three-component fits are shown in Figure 4. The high IS, high QS doublet characteristic of Fe 2+ in either 6-or 8-coordination, which typically has QS ∼3.5 (Woodland and O'Neill 1993;Eeckhout et al 2002;Geiger et al 2003;Taran et al 2007;Woodland et al 2009) was completely absent from all spectra, further confirming that no Fe 2+ was present in our samples.…”

Section: Mössbauer Spectroscopysupporting

confidence: 71%

“…These values are presented without error bars because rather than being direct measurements, they are the optimized values yielding the best fit to the spectroscopic data as shown in the residuals in Figure 4. [Data sources: Amthauer et al (1976), O'Neill (1993), Fei et al (1994), Eeckhout et al (2002), Geiger et al (2003), McCammon et al (2004), Sharma et al (2007), Taran et al (2007), Grew et al (2008), Woodland et al (2009).] (Color online.)…”

Section: Power X-ray Diffractionmentioning

confidence: 99%

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Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite

Hummer

Fei

2012

American Mineralogist

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We have synthesized magnesium-iron silicate perovskites with the general formula Mg 1-x Fe 3+ x+y Si 1-y O 3 , in which the iron cation is exclusively trivalent. To investigate the crystal chemistry of Fe 3+ -bearing perovskite, six samples (both with and without Al) were analyzed using scanning electron microscopy, electron microprobe, X-ray diffraction, and Mössbauer spectroscopy. Results indicate that Fe 3+ substitutes significantly into both the octahedral and dodecahedral sites in the orthorhombic perovskite structure, but prefers the octahedral site at Fe 3+ concentrations between 0.04 and 0.05 Fe per formula unit, and the dodecahedral site at higher Fe 3+ concentrations. We propose a model in which Fe 3+ in the A/B site (in excess of that produced by charge coupled substitution) is accommodated by Mg/O vacancies. Hyperfine parameters refined from the Mössbauer spectra also indicate that a portion of dodecahedral sites undergo significant structural distortion. The presence of Fe 3+ in the perovskite structure increases the unit-cell volume substantially compared to either the Mg end-member, or Fe 2+ -bearing perovskite, and the addition of Al did not significantly alter the volume. Implications for increased compressibility and a partially suppressed spin transition of Fe 3+ in lower mantle perovskite are also discussed.

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Section: Mössbauer Spectroscopysupporting

confidence: 71%

Section: Power X-ray Diffractionmentioning

confidence: 99%

Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite

Hummer

Fei

2012

American Mineralogist

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“…center in which the electron is excited first to a higher energetic level and then falls back to any one of the different centers with equal probability. In the absorption spectra of natural Fe-rich garnets [29], the absorption bands in the near IR range are also observed and connected with the electronic d-d transfer transitions 5 E g ? 5 T 2g in Fe 2?…”

Section: Samples and Experimental Detailsmentioning

confidence: 88%

“…The information about optical properties of the bismuth ferrite in the range between 0.3 and 1 eV is absent as we know. So, we will consider the optical data for other materials containing Fe ions, for example iron yttrium garnet [28] or natural Fe-rich garnets [29].…”

Section: Samples and Experimental Detailsmentioning

confidence: 99%

IR absorption and linear dichroism in BiFe0.5Co0.5O3 films

et al. 2015

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The optical density spectra D(hx) of BiFe 0.5-Co 0.5 O 3 films with thickness d = 230 and 1400 nm on LaAlO 3 substrate were studied in the infrared range from 0.09 to 1.65 eV in unpolarized and linear polarized light at room temperature and at T = 80 K in the magnetic field of 4.5 kOe and without the field. The absorption bands at hx *0.2 and *0.7 eV are revealed in the D(hx) spectra recorded in unpolarized light and attributed to combination of two-phonon and two-magnon absorption and to dd transitions in Fe or Co ions, respectively. In the D(hx) spectra of BiFe 0.5 Co 0.5 O 3 film with d = 230 nm recorded in linear polarized light, the additional bands in the range of 0.3 eV-1.0 eV are found and explained by the nonuniform charge state due to the existence of weakly conductive electric domains and domain walls with higher conductivity and by the scattering of the light on the domains. The position of the bands in the optical density spectra in polarized light D \ (hx) and D jj (hx) depends on the direction of the magnetic field relative to the film and on the temperature, which is explained by the change of the electric domain sizes. The revealed dependence of the optical properties on the magnetic field direction allows recommending BiFe 0.5 Co 0.5 O 3 films as new functional magneto-optical material.

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“…Absorption spectra of Mg 0.9 Fe 0.1 SiO 4 olivine has been described by Hofmeister () that based on her measurements and low‐temperature spectra from Taran and Langer () and high‐temperature from Ullrich et al (). We also use low‐temperature spectra from Taran and Langer () and Taran et al () for (Mg 1.63 Fe 0.27 Ca 0.04 Al 0.02 ) [6] Si 1.97 Al 0.03 O 6 clinopyroxene, (Ca 0.84 Na 0.12 Fe 0.01 ) [8] (Mg 0.91 Fe 0.07 Cr 0.02 ) [6] Si 2.03 O 6 orthopyroxene, and (Mg 1.282 Fe 1.312 Mn 0.028 Ca 0.413 ) [8] (Fe 0.04 Al 1.97 Si 2.971 ) [6] O 12 garnet. For pyroxene spectra we approximate the average of crystallographic orientations.…”

Section: Predictions Of Krad In the Upper Mantlementioning

confidence: 99%

New Constraints on the Thermal Conductivity of the Upper Mantle From Numerical Models of Radiation Transport

Grose

Afonso

2019

Geochem Geophys Geosyst

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To address uncertainties in the values and mathematical form of the radiative thermal conductivity krad in the mantle, we developed new models for the transport, scattering, and absorption of thermal radiation in semitransparent multiphase polycrystalline assemblages. We show that the Rosseland diffusion equation correctly describes the diffusion of thermal radiation and infer the form of the effective spectral coefficients through numerical experimentation. We show that the scattering coefficient depends on the grain size and on interphase contact statistics in complicated ways, but that simplifications can be employed in practice. The effective opacity of a composite random material is a harmonically weighted mixture in the limit of infinitely large grain size and an arithmetically weighted mixture in the limit of infinitesimal grain size. Using existing absorption spectra for major upper mantle minerals, we estimate krad as a function of temperature, grain size, and petrology. In mantle assemblages, the scattering effect is important for small grain sizes (<1 mm), but the grain size effect on the effective opacity of a multiphase medium is important for grain sizes up to 10 cm. We calculate that upper mantle krad is about 2–3.5 W·m−1·K−1 for a representative mean grain size range of 0.01 to 1 cm. This translates to a total thermal conductivity of 5.5–7 W·m−1·K−1. Application of our model to the cooling of oceanic lithosphere shows that krad increases net cooling by about 25%.

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Optical absorption study of natural garnets of almandine-skiagite composition showing intervalence Fe2+ + Fe3+ -> Fe3+ + Fe2+ charge-transfer transition

Cited by 25 publications

References 14 publications

Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite

Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite

IR absorption and linear dichroism in BiFe0.5Co0.5O3 films

New Constraints on the Thermal Conductivity of the Upper Mantle From Numerical Models of Radiation Transport

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