Evidence for absorption by exchange-coupled Fe2+-Fe3+ pairs in the near infra-red spectra of minerals

Smith, G.

doi:10.1007/bf00311848

Cited by 54 publications

(13 citation statements)

References 12 publications

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“…Compared to olivine, the extinction coeffi cient increased by more than a factor of ten, despite that the coordination polyhedron around Fe 2+ in ringwoodite is less distorted than in olivine. A similar intensifi cation of the crystal fi eld bands of Fe 2+ has been observed in several silicate minerals containing both Fe 2+ and Fe 3+ in adjacent polyhedra (Smith 1978;Mattson and Rossman 1987). However, the physical mechanism behind this intensifi cation is not yet fully understood.…”

Section: Absorption Spectrum At 1 Barmentioning

confidence: 80%

Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle

Keppler

Smyth

2005

American Mineralogist

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Section: Absorption Spectrum At 1 Barmentioning

confidence: 80%

Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle

Keppler

Smyth

2005

American Mineralogist

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“…5, EA-2). The features at ϳ 725, 920, and 1195 nm are related to the presence of Fe 2ϩ or Fe 3ϩ -Fe 2ϩ charge transfer (Faye, 1968;Robbins and Strens, 1972;Smith and Strens, 1976;Smith, 1978;Kliem and Lehmann, 1979). Changes in the Fe-dominated region of the NIR spectrum after reaction are somewhat pH-dependent.…”

Section: Solids Characterizationmentioning

confidence: 96%

Transient and quasi-steady-state dissolution of biotite at 22–25°C in high pH, sodium, nitrate, and aluminate solutions

Samson¹,

Nagy²,

Cotton³

2005

Geochimica et Cosmochimica Acta

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“…S2), as would be expected for single-ion crystal field bands, suggesting that the absorption of light by the A-site HS Fe 2+ is enhanced by interactions with the edge-sharing B-site Fe 3+ . Indeed, exchange-coupling interactions of adjacent transition metal ions have been employed to explain the anomalous temperature and concentration behavior of the crystal field bands 27,28 . However, the importance of this transition mechanism for the absorption coefficient of lower mantle minerals has been previously overlooked.…”

mentioning

confidence: 99%

Radiative conductivity and abundance of post-perovskite in the lowermost mantle

Lobanov

Holtgrewe

Lin

et al. 2017

Earth and Planetary Science Letters

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Thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary-scale geological processes. Yet, there are no direct experimental measurements of thermal conductivity at relevant pressure-temperature conditions of Earth's core-mantle boundary. Here we determine the radiative conductivity of post-perovskite at near core-mantle boundary conditions by optical absorption measurements in a laser-heated diamond anvil cell. Our results show that the radiative conductivity of Mg 0.9 Fe 0.1 SiO 3 post-perovskite (< 1.2 W/m/K) is ~ 40% smaller than bridgmanite at the base of the mantle. By combining this result with the present-day core-mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post-perovskite is as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep Earth. Main textThe lowermost 200-400 km of the mantle is a critical region responsible for the coremantle interaction powering all major geological processes on Earth 1 . Specifically, thermal conductivity of the thermal boundary layer (TBL) above the core-mantle boundary (CMB) determines the heat flow out of the core that provides energy to sustain the mantle global circulation and to drive the geodynamo 1, 2 . Seismic structures of the lowermost mantle, however, are complex 3, 4 implying that the thermal conductivity of the region is non-uniform due to variations in chemical (e.g. iron) and/or mineralogical contents as well as texturing of the constituting minerals. The nature of the seismic heterogeneity near the CMB, including a sharp increase in shear wave velocity and anti-correlations of seismic parameters, has been linked to the bridgmanite (Bdgm) to post-perovskite (Ppv) transition 5, 6 , as these phases have contrasting elastic, rheological, and transport properties (e.g. Ref. 6 ). Indeed, measurements and computations of lattice thermal conductivity (k lat ) in Bdgm and Ppv revealed that Ppv conducts heat 50-60 % more efficiently than Bdgm 7, 8 , suggesting that the distribution of the Ppv phase can significantly enhance the heat flux out of the core. However, no mineral physics constraints are available on the radiative thermal conductivity (k rad ) of Ppv, which should play an increasingly important role at high temperature 9 , as well as on the Ppv abundance in the lowermost mantle. This has hampered our understanding of how the heat flux across the CMB may vary laterally and what magnitude of the energy source in the mantle and the outer core is needed to power their convections.Previous estimates of radiative thermal conductivity at lower mantle conditions were based on high-pressure room-temperature measurements of the absorption coefficients of representative minerals in the mid/near-infrared and visible spectral range [10][11][12][13][14] . The presence of an intense thermal radiation emitted from the hot sample makes measurements of the optical properties at high temperatures releva...

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Evidence for absorption by exchange-coupled Fe2+-Fe3+ pairs in the near infra-red spectra of minerals

Cited by 54 publications

References 12 publications

Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle

Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle

Transient and quasi-steady-state dissolution of biotite at 22–25°C in high pH, sodium, nitrate, and aluminate solutions

Radiative conductivity and abundance of post-perovskite in the lowermost mantle

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