Electrical and photoadsorptive properties of valence-controlled .alpha.-iron hydroxide oxide

Kaneko, Katsumi; Inoue, N.; Ishikawa, Toshiaki

doi:10.1021/j100342a056

Cited by 19 publications

(8 citation statements)

References 9 publications

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“…Latta et al [37] found that Al-substitution in goethites reduced the Fe atom exchange rate between Fe(II) aq and Al-goethites, and that the reduced electron conductivity in the bulk mineral resulted from the surface Al-coating. As shown in Figure 2, the morphology of Cr-goethites transformed from an acicular nature into a rod-like nature with a smaller diameter than that of pure goethite, which would result in a reduction in conductivity [39]. Based on previous reports and our results, the lower Fe atom exchange rates in goethite with Cr-substitutions were expected to have a higher degree of crystallinity and lower bulk conductivity.…”

Section: Influence Of Cr-substitution On Fe Atom Exchange and Electrosupporting

confidence: 66%

<strong>Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization</strong>

Liu

Hua

Chen³

et al. 2018

Proceedings of the 1st International Electronic Conference on Mineral Science

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Abstract:The interaction between aqueous Fe(II) (Fe(II) aq ) and iron minerals is an important reaction of the iron cycle, and it plays a critical role in impacting the environmental behavior of heavy metals in soils. Metal substitution into iron (hydr)oxides has been reported to reduce Fe atom exchange rates between Fe(II) aq and metal-substituted iron (hydr)oxides and inhibit the recrystallization of iron (hydr)oxides. However, the environmental behaviors of the substituted metal during these processes remain unclear. In this study, Fe(II) aq -induced recrystallization of Cr-substituted goethite (Cr-goethite) was investigated, along with the sequential release behavior of substituted Cr(III). Results from a stable Fe isotopic tracer and Mössbauer characterization studies show that Fe atom exchange occurred between Fe(II) aq and structural Fe(III) (Fe(III) oxide ) in Cr-goethites, during which the Cr-goethites were recrystallized. The Cr substitution inhibited the rates of Fe atom exchange and Cr-goethite recrystallization. During the recrystallization of Cr-goethites induced by Fe(II) aq , Cr(III) was released from Cr-goethite. In addition, Cr-goethites with a higher level of Cr-substituted content released more Cr(III). The highest Fe atom exchange rate and the highest amount of released Cr(III) were observed at a pH of 7.5. Under reaction conditions involving a lower pH of 5.5 or a higher pH of 8.5, there were substantially lower rates of Fe atom exchange and Cr(III) release. This trend of Cr(III) release was similar with changes in Fe atom exchange, suggesting that Cr(III) release is driven by Fe atom exchange. The release and reincorporation of Cr(III) occurred simultaneously during the Fe(II) aq -induced recrystallization of Cr-goethites, especially during the late stage of the observed reactions. Our findings emphasize an important role for Fe(II) aq -induced recrystallization of iron minerals in changing soil metal characteristics, which is critical for the evaluation of soil metal activities, especially those in Fe-rich soils.

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Section: Influence Of Cr-substitution On Fe Atom Exchange and Electrosupporting

confidence: 66%

<strong>Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization</strong>

Liu

Hua

Chen³

et al. 2018

Proceedings of the 1st International Electronic Conference on Mineral Science

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“…Below 45 GPa, ε-FeOOH is well de ned as an insulating phase. It has the same small polaron hopping conduction as many other insulating hydroxide or hydrous minerals 38 . At 53.5 GPa, a second semi-circular arc appears in the low frequency region next to the main circle (Fig.…”

Section: Resultsmentioning

confidence: 96%

Metallized ε-FeOOH and the heterogeneous electrical conductivity structure in the lower mantle

Zhuang

Cui

Tang

et al. 2020

Preprint

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Electrical heterogeneity at the depth of 900-1400 km in Earth’s interior is a key factor to constrain the minor phase composition of the lower mantle. However, prevailing mineralogical models including Fe- or Al-enriched silicates or ferropericlase are insufficient to explain the ultra-high electrical conductivity in local areas of subduction slabs. Here, we measure the electrical conductivity of ε-FeOOH up to 61 GPa. A 3-order abrupt jump of electrical conductivity is observed in 45-50 GPa, reaching 1.24±0.19 × 103 S/m at 61 GPa. Density mean field theory simulations suggest that ε-FeOOH undergoes a Mott-type electronic transition, which leads the conduction mechanism to switch from small polaron conduction to free electron conduction. Compared with bridgmanite, ferropericlase and conventional mantle compositional models, the electrical conductivity of the metallic ε-FeOOH is 1-3 orders of magnitude higher. Minor or moderate incorporation of metallic ε-FeOOH into the ambient lower mantle could reproduce the observed electrical heterogeneity derived from geomagnetic data at 900-1400 km depth.

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“…FeZQ has an extra d-electron, a so-called quasi-free electron.126, 271 The increase in the quasi-free electron" 6] concentration with doping varies the electrical and optical properties of a-Fe,O, . Figure 2 shows varaition of the electrical conductivity of Ti-doped a-Fe,O, filmsr281 and powder [29] with the dopant amount at 303 K. The conductivity of the powder steeply increases with doping up to 3 atomic-% due to a significant segregation effect. This increase is due to the creation of quasi-free electrons, which leads not only to an increase in the carrier concentration, but also to a decrease in the activation energy for conduction.…”

Section: Homogeneous Valence Controlled Oxide 4 Instable Phase Formamentioning

confidence: 99%

Transition metal oxide films

Uekawa

Kaneko

1995

Advanced Materials

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The sol‐gel method can be used to produce multicomponent oxide materials which have a homogeneous composition even at the atomic level. Thin transition metal oxide films are shown to exhibit different properties from those of the bulk materials and both the crystal structure and the valence state of the materials can be sensitively controlled by doping. Recent progress in the field is reviewed, including the production of highly oriented films, valence‐controlled oxides, the control of instable phase formation and atmosphere‐sensitive structural transformations.

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Electrical and photoadsorptive properties of valence-controlled .alpha.-iron hydroxide oxide

Cited by 19 publications

References 9 publications

<strong>Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization</strong>

<strong>Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization</strong>

Metallized ε-FeOOH and the heterogeneous electrical conductivity structure in the lower mantle

Transition metal oxide films

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