Structure of the metastable modification of iron(III) oxide

Burgina, E. B.; Kustova, G. N.; Tsybulya, S. V.; Kryukova, G. N.; Litvak, G. S.; Исупова, Л. А.; Садыков, В. А.

doi:10.1007/bf02741997

Cited by 17 publications

(26 citation statements)

References 12 publications

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“…Similarly, other scientists have ascribed non-uniform peak broadening to unusual behaviors with respect to particle morphology, size, microporosity, strain, and stacking faults (Watari et al 1979a(Watari et al , 1979b(Watari et al , 1983Jiang et al 2000;Fan et al 2006). Burgina et al (2000b) counter that morphological and defect features might possibly explain the anomalies in XRD data but not those in the IR spectra. These authors thus support the existence of hydrous hematite-like phases, and they additionally argue that the crystal structures of the precursor phases must be symmetrically different from that of hematite.…”

Section: Doubts Concerning Protohematite and Hydrohematitementioning

confidence: 95%

“…Kustova et al (1992) and others assign additional lines in the IR spectra (3200-3500 and 900-1050 cm -1 ) to structural OHgroups in protohematite (Burgina et al 2000b;Chernyshova et al 2007). An additional band at ~630 cm -1 , they assert, is due either to quasi-tetrahedral defects in the protohematite structure or to OH -substitution (Yariv and Mendelovici 1979;Burgina et al 2000b). Wolska and Szajda (1985) state that the ~3400, 900-950, and 630 cm -1 bands are characteristic of hydrohematite.…”

Section: Recent History-protohematite and Hydrohematitementioning

confidence: 96%

“…Moreover, several research groups have observed a difference in the infrared (IR) and Raman spectra of stoichiometric hematite and antecedent phases (Wolska and Szajda 1985;Kustova et al 1992;Sadykov et al 1996;Burgina et al 2000aBurgina et al , 2000b. According to Burgina et al (2000b), protohematite is identified by shifts in certain IR spectral peaks (308, 445, and 530 cm -1 ) relative to stoichiometric hematite (333, 468, and 543 cm -1 ). Kustova et al (1992) and others assign additional lines in the IR spectra (3200-3500 and 900-1050 cm -1 ) to structural OHgroups in protohematite (Burgina et al 2000b;Chernyshova et al 2007).…”

Section: Recent History-protohematite and Hydrohematitementioning

confidence: 97%

“…According to Burgina et al (2000b), protohematite is identified by shifts in certain IR spectral peaks (308, 445, and 530 cm -1 ) relative to stoichiometric hematite (333, 468, and 543 cm -1 ). Kustova et al (1992) and others assign additional lines in the IR spectra (3200-3500 and 900-1050 cm -1 ) to structural OHgroups in protohematite (Burgina et al 2000b;Chernyshova et al 2007). An additional band at ~630 cm -1 , they assert, is due either to quasi-tetrahedral defects in the protohematite structure or to OH -substitution (Yariv and Mendelovici 1979;Burgina et al 2000b).…”

Section: Recent History-protohematite and Hydrohematitementioning

confidence: 99%

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A refined monoclinic structure for a variety of "hydrohematite"

Peterson

Heaney

Post

et al. 2015

American Mineralogist

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In ferruginous soils, nano-to microscale hematite (a-Fe 2 O 3 ) plays a central role in redox processes and contaminant cycling. Hematite is known to incorporate structural OH -and water, and the requisite charge balance is achieved by iron vacancies. Prior researchers have suggested that the defective hematite structures form unique phases called "protohematite" and "hydrohematite." Infrared and Raman spectroscopic studies have assigned a lower-symmetry space group to "hydrohematite" (R3c) relative to that of stoichiometric hematite (R3c). However, the existence and structure of these phases have been contentious, largely due to the lack of in situ X-ray diffraction dataHere we present a new structure refinement for "hydrohematite" precipitated hydrothermally at 200 °C in a monoclinic space group (I2/a) using time-resolved synchrotron X-ray diffraction (TR-XRD) data collected during the in situ hydrothermal precipitation of akaganeite and its transformation to stoichiometric hematite. Distinct peak splitting was observed in the "hydrohematite" diffraction patterns, indicating a violation of the threefold rotational symmetry. A monoclinic unit cell with parameters of a = 7.3951(10), b = 5.0117(5), c = 5.4417(7) Å, b = 95.666(5)° provided a good fit and significant reduction in c 2 and R wp relative to space group R3c. Rietveld analyses revealed that water concentrations in the first-formed crystals of "hydrohematite" were comparable to water contents of akaganeite and goethite. Thus, the hydrothermal transformation of akaganeite to "hydrohematite" is promoted not by dehydration but by reconstruction of the oxygen framework.

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Section: Doubts Concerning Protohematite and Hydrohematitementioning

confidence: 95%

Section: Recent History-protohematite and Hydrohematitementioning

confidence: 96%

Section: Recent History-protohematite and Hydrohematitementioning

confidence: 97%

Section: Recent History-protohematite and Hydrohematitementioning

confidence: 99%

See 2 more Smart Citations

A refined monoclinic structure for a variety of "hydrohematite"

Peterson

Heaney

Post

et al. 2015

American Mineralogist

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“…This observation suggests that at 700°C, protohematite still exists, being consistent with Gualtieri and Venturelli finding [75] that the conversion of protohematite to fully developed hematite takes place at 800°C. Several works [e.g., 92,93] showed that this transformation could start at even higher temperature, above 900°C.…”

Section: Xrd and Ftir Analysesmentioning

confidence: 99%

Mineral transformations and textural evolution during roasting of bog iron ores

Rzepa

Bajda

Gaweł

et al. 2015

J Therm Anal Calorim

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The processes occurring during roasting of bog iron ores were characterized using TG-DTG-DTA-QMS, XRD, FTIR and specific surface analysis. Removal of physically adsorbed water is followed by dehydroxylation of iron oxyhydroxides and oxidation of organic matter at 200-600°C. The main product of the transformations is disordered nanocrystalline (proto)hematite or hematite/-maghemite mixture, depending on organic matter content and heating conditions. The conversion of iron oxyhydroxides to hematite occurs at temperatures different than those reported for pure compounds. At higher temperatures, protohematite undergoes recrystallization to the stoichiometric hematite, and manganese oxides are partially reduced. At 1000°C, the roasting products consist of hematite and cristobalite together with Mn-Fe spinels if the initial ore contained Mn oxides. The admixtures of various secondary silicates were encountered as well. Low-to moderate-temperature roasting slightly affects the specific surface area and lowers volume of micropores. The hightemperature transformations lead to decrease in the specific surface area and to the destruction of porous texture of the bog iron ores. Although the general course of the processes during roasting was similar in all the samples, some of their details as well as mineralogy and properties of the products are highly dependent on the composition of the initial material.

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Identification of Three Coexistent Defect Types in Hematite Photoanodes through Structure–Property Analysis

2021

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Structural defects present in hematite photoanodes are analyzed by correlating parameters derived from Raman spectra, band structure measurements and photoelectrochemical (PEC) oxygen evolution reaction performance. A series of photoanodes with varying quality of hematite are prepared by sintering akaganeite films with a systematically varied protocol. Data acquired through Raman microscopy, linear sweep voltammetry, and electrochemical impedance spectroscopy is parametrized and systematically compared to detect relationships amongst the data. Correlations between the structural information contained within the Raman spectra and PEC parameters enable the identification of three types of structural defects within the material. Each defect type is found to exert unique influence on PEC behavior and each became dominant under specific fabrication conditions. A straightforward approach to detecting defects in photoelectrodes and identifying their influence on photoelectrode properties and behavior is provided.

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Structure of the metastable modification of iron(III) oxide

Cited by 17 publications

References 12 publications

A refined monoclinic structure for a variety of "hydrohematite"

A refined monoclinic structure for a variety of "hydrohematite"

Mineral transformations and textural evolution during roasting of bog iron ores

Identification of Three Coexistent Defect Types in Hematite Photoanodes through Structure–Property Analysis

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