A Superstructure in Spinels

Braun, P. B.

doi:10.1038/1701123a0

Cited by 325 publications

(112 citation statements)

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“…The extent of order amongst the cation vacancies has been investigated (e.g. [140][141][142][143]) and there is evidence that three different vacancy distributions can occur depending on the size of the crystals [144] and preparation conditions:…”

Section: Bulk Defects 29mentioning

confidence: 99%

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Iron oxide surfaces

Parkinson

2016

Surface Science Reports

501

463

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The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), hematite (α-Fe 2 O 3 ), and wüstite (Fe 1-x O) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe 3 O 4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment, and because it is an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed.The best understood iron oxide surface at present is probably Fe 3 O 4 (100); the structure is known with a high degree of precision and the major defects and properties are well characterised. A major factor in this is that a termination at the Fe oct -O plane can be reproducibly prepared by a variety of methods, as long as the surface is annealed in 10 Such straightforward preparation of a monophase termination is generally not the case for other iron oxide surfaces. All available evidence suggests the oft-studied (√2×√2)R45° reconstruction results from a rearrangement of the cation lattice in the outermost unit cell in which two octahedral cations are replaced by one tetrahedral interstitial, a motif conceptually similar to well-known Koch-Cohen defects in Fe (0001) is the most studied hematite surface, but 2 difficulties preparing stoichiometric surfaces under UHV conditions have hampered a definitive determination of the structure. There is evidence for at least three terminations: a bulk-like termination at the oxygen plane, a termination with half of the cation layer, and a termination with ferryl groups. When the surface is reduced the so-called "bi-phase" structure is formed, which eventually transforms to a Fe 3 O 4 (111)-like termination. The structure of the bi-phase surface is controversial; a largely accepted model of coexisting Fe 1-x O and α-Fe 2 O 3 (0001) islands was recently challenged and a new structure based on a thin film of Fe 3 O 4 (111) on α-Fe 2 O 3 (0001) was proposed. The merits of the compet...

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Section: Bulk Defects 29mentioning

confidence: 99%

“…(1) cubic structure with random distribution of the vacancies (space group Fd3m); (2) vacancies distributed as the Li cations in LiFe 5 O 8 (space group P4 3 32) [140] (3) an ordered distribution of the vacancies with tetragonal symmetry and a three-fold doubling along the c-axis (space group P4 1 2 1 2) [145].…”

Section: Bulk Defects 29mentioning

confidence: 99%

Iron oxide surfaces

Parkinson

2016

Surface Science Reports

501

463

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“…In the normal spinels, the A 2+ ions are contained in the tetrahedral holes, and the B 3+ in the octahedral holes. In the inverse spinels, on the other hand, the A 2+ ions and half the B 3+ ions are in octahedral holes, and the remaining B 3+ ions are in tetrahedral holes [9][10][11][12] In fact, very few spinels have exactly the normal or inverse structure, and these are sometimes called mixed spinels. Li 2 ZnTi 3 O 8 presents a derived spinel structure with P4 3 32 space group, in which the octahedral 12d and 4b sites are occupied by Ti and Li respectively, and the tetrahedral 8c sites are shared by Zn and Li, suggesting an intermediary spinel structure [13][14][15] .…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Properties of pigment Li2-xZn1-xPrxTi3O8

et al. 2016

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Inorganic compounds doped with rare earths (Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Tm 3+ ) have been used in various applications including light-emitting devices such as fluorescent lamps, cathode ray tubes, lasers and inorganic pigments. In this study, Pr 3+ is doped in spinel Li 2 ZnTi 3 O 8 system and synthesized by the polymeric precursor method, which is based on the process developed by the Pechini, and characterized by X-ray diffraction, UV-visible and CIE-L colorimetric measures * a * b *., in order to study the effect of doping and thermal treatment on its colorimetric properties. With three different samples of Pr 3+ doping (0.01; 0.05 and 0.1 mol%) were prepared and calcined at 500°C, 600°C, 700°C, 800°C and 900°C for 4 h. The analysis of X-ray diffraction confirmed the formation of pure phases with spinel structure and average crystallite size of less than 46 nm. It was found that the colorimetric properties ranging from green to red, in accordance with the increase in the concentration of Pr 3+ and thermal processing temperature.

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“…Because of the ease with which maghemite can be prepared from magnetite in the presence of water, it has been suggested that hydrogen enters the lattice of maghemite. Braun (1952) suggested its presence as OH-ions and Aharoni, Frei and Schieber (1962) suggested the presence of H+ ions in the vacant sites. As will be evident from Table I, the latter suggestion is contrary to experimental magnetic evidence while there may yet be some truth in Braun's suggestion or that of Sinha and Sinha (1957).…”

Section: Crystallographic and Magnetic Structurementioning

confidence: 99%

On the Transition of Magnetite to Haematite and its Implications to Rockmagnetism

Banerjee

1965

J. geomagn. geoelec

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The problems in the crystallographic structure of maghemite is first critically reviewed and magnetic evidences for a superstructure presented. A nondestructive method was used to find maghemite's Curie point and the latter shown to be coincident with its crystallographic transition temperature. The implications of this discovery for rockmagnetism are discussed, including the possibility of a pressure induced remagnetizaiton.

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A Superstructure in Spinels

Cited by 325 publications

References 2 publications

Iron oxide surfaces

Iron oxide surfaces

Spectroscopic Properties of pigment Li2-xZn1-xPrxTi3O8

On the Transition of Magnetite to Haematite and its Implications to Rockmagnetism

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