Dielectric constants of tephroite, fayalite and olivine and the oxide additivity rule

Shannon, R. D.; Subramanian, M.A.; Hosoya, S.; Rossman, George R.

doi:10.1007/bf00199037

Cited by 31 publications

(12 citation statements)

References 36 publications

(26 reference statements)

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“…Comparing Fig. 6(a) to the ideal behaviour of n at infinite wavelength, the average CDA fit n value at zero frequency for Fo 0 () is in good agreement with the average dielectric function for fayalite determined by Shannon et al (1991) (). n at long λ for forsterite should be 2.64 (based on a simple average of ε ν=0 = 6.867, 7.392, 6.739 for each polarization, Shannon & Subramanian 1989), which is in rough agreement but slightly above the value of 2.1 predicted from Fig.…”

Section: Discussionsupporting

confidence: 70%

Infrared laboratory absorbance spectra of olivine: using classical dispersion analysis to extract peak parameters

Pitman

Dijkstra

Hofmeister³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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Laboratory measurements quantifying the effect of Fe substituting for Mg in olivine are needed to distinguish compositional from temperature, grain size and grain shape effects in observational data. To address this need, we study room temperature absorption spectra of a large suite of olivines evenly spaced across Mg and Fe compositions. We apply the principle that classical dispersion theory may be used to determine peak positions as well as peak widths, strengths and possibly optical function (n(λ) and k(λ)) estimates from absorption spectra of thin film samples of these olivines and two additional isotropic and anisotropic minerals with varying hardness and numbers of spectral bands. For olivine, we find that this method provides good estimates of peak position and that accounting for asymmetric peak shapes in this way increases the error on full width at half‐maximum and oscillator strengths. Values from classical dispersion fits better match published n and k derived from reflectivity of single crystals when the dust proxy is soft and the thickness of the sample is independently constrained. Electronic data and peak parameter trends for the laboratory olivine absorption spectra and the viability of the extracted n and k are discussed with regard to astronomy.

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Section: Discussionsupporting

confidence: 70%

Infrared laboratory absorbance spectra of olivine: using classical dispersion analysis to extract peak parameters

Pitman

Dijkstra

Hofmeister³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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“…Though the dielectric constants of the minerals were not fitted while developing the potential, we examined how well their values were predicted by the newly developed potential. The values were calculated using GULP [ Gale and Rohl , ] and are tabulated along with the experimental values [ Shannon et al , ; Olhoeft , ] in Table . For forsterite and fayalite, we notice that while all three diagonal components of the predicted dielectric constants are much lower than those from experiments, they agreed in their relative strengths with those from experiments.…”

Section: Atomic‐scale Simulation Methodologymentioning

confidence: 99%

“…Forsterite and fayalite values from experiments are taken from Shannon et al [], and the orthopyroxene values (i.e., enstatite and ferrosilite) are taken from Olhoeft []. The values from Tilocca et al [] were computed using a shell model.…”

Section: Atomic‐scale Simulation Methodologymentioning

confidence: 99%

Atomic‐scale simulation of space weathering in olivine and orthopyroxene

Quadery

Pacheco

et al. 2015

JGR Planets

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(2015), Atomic-scale simulation of space weathering in olivine and orthopyroxene, J. Geophys. Res. Planets, 120, 643-661, doi:10.1002 Abstract Classical molecular dynamics was used to study the annealing of anion and cation Frenkel defects in olivine and orthopyroxene minerals. While it was found that for both minerals, reorganization of the Si-O bonds, often accompanied by large Si displacements, occurs to maintain the fourfold coordination of the SiO 4 tetrahedra, important differences are observed in their annealing behavior. Specifically, cation defects are substantially more mobile in olivine than in orthopyroxene leading to rapid annihilation of cation Frenkel defects and formation of extended defects in olivine. By contrast, the diffusion rate of anion defects in orthopyroxene is much higher than that in olivine and also exhibits large anisotropy. Consequently, it was found that diffusion in orthopyroxene occurs without significant annihilation of anion Frenkel defects or trapping of anion interstitials or vacancies into clusters. The results obtained here are discussed in the context of space weathering of olivine and orthopyroxene. Specifically, two important observations are made which may explain previous experimental results. First, ion irradiation experiments that show reduced tolerance for radiation damage in orthopyroxene may be explained by the rapid, one-dimensional anion mobility which prevents healing of the lattice. Second, laser heating experiments which show that orthopyroxene has enhanced tolerance to reduction and the evolution of nanophase Fe inclusions could be due to the observed rapid anion diffusion in orthopyroxene, which might allow the bulk to act as a reservoir for the surface.

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“…A theory by Debye and Conwell (1954) implies that a constant α depends on the electric charge of the species (proton) and the dielectric constant of the material. Since dielectric constant of a mineral does not change so much among minerals (e.g., Shannon et al 1992Shannon et al , 1991, α should not depend so much on minerals. The reported values of α for olivine by Poe et al (2010) are larger than other estimated values by a factor of 10 to 50 that is at odd from the theoretical point of view.…”

Section: Parameterization Of Electrical Conductivity: Does Activationmentioning

confidence: 99%

Some remarks on hydrogen-assisted electrical conductivity in olivine and other minerals

Karato

2019

Prog Earth Planet Sci

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Electrical conductivity in minerals is sensitive to hydrogen content, and therefore, it is a potentially important property from which one can infer hydrogen (water) distribution in the mantle. However, there has been much confusion in the reported results on hydrogen-assisted conductivity. In this paper, I review the existing experimental observations on hydrogenenhanced electrical conductivity in olivine and other minerals to identify the causes of confusion. Hydrogen loss as well as hydrogen gain could occur during a conductivity measurement at high pressures and temperatures. Particularly important is the unrecognized hydrogen gain during an experiment that could lead to a large degree of error. Many experiments were conducted under the conditions where specimens were super-saturated with hydrogen making the validity of those results unclear. A model for hydrogen loss is developed showing a strategy by which hydrogen loss can be minimized. When one selects the experimental results in which the influence of hydrogen loss/gain are carefully examined, there is no major discrepancy among the results from different laboratories except differences between the results from low and high temperatures. Differences between low-temperature and high-temperature results are caused by the change in conduction mechanism. At low temperatures, conduction is due to the migration of interstitial ("free") proton and is nearly isotropic, whereas conduction at high temperatures is due to the migration of two protons at M-site that is highly anisotropic. There is no evidence for substantial concentration dependence of activation enthalpy. Observed exceptionally large concentration dependence reported by Poe et al. (Phys Earth Planet Inter 181:103-111, 2010) is inconsistent with all other reports and is likely caused by some experimental artifact. Experimental results in the high-temperature regime explain a majority of geophysical observations on the conductivity of the oceanic asthenosphere: partial melting is not needed in most regions and is rather inconsistent with the observations on the matured oceanic mantle. Exception is the asthenosphere near the ridge and/or near the trench where very high conductivity (~0.1 S/m) is reported at the top of the asthenosphere. Partial melting might play some role in these regions. Electrical conductivity in the continental lithosphere cannot be attributed entirely to olivine. An important role of orthopyroxene and/or other minor materials (graphite, sulfide) is needed to explain high conductivity reported in some regions such as Bushveld in South Africa. The largest remaining uncertainty is the degree to which hydrogen affects electrical conductivity in the lower mantle minerals. Determining the influence of hydrogen on electrical conductivity in lower mantle minerals is critical to make progress in understanding the global water circulation.

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Dielectric constants of tephroite, fayalite and olivine and the oxide additivity rule

Abstract: Abstract.The dielectric constants and dissipation factors of synthetic tephroite (Mn2SiO4), fayalite (Fe2SiO4) and a forsteritic olivine (Mga.soFeo.2zSiO4) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are:

Cited by 31 publications

References 36 publications

Infrared laboratory absorbance spectra of olivine: using classical dispersion analysis to extract peak parameters

Infrared laboratory absorbance spectra of olivine: using classical dispersion analysis to extract peak parameters

Atomic‐scale simulation of space weathering in olivine and orthopyroxene

Some remarks on hydrogen-assisted electrical conductivity in olivine and other minerals

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