Crystal structures and cation distributions in simple spinels from powder XRD structural refinements: MgCr2O4, ZnCr2O4, Fe3O4 and the temperature dependence of the cation distribution in ZnAl2O4

O’Neill, Hugh; Dollase, W. A.

doi:10.1007/bf00211850

Cited by 223 publications

(101 citation statements)

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“…[5,[28][29][30] Compared with the cationic re-distribution in spinel nanocrystals at moderate temperature (typically 350-600 8C), [12][13][14] electric potential-driven ionic motion in battery materials, [15,16] and ionic rearrangements in bulk oxides (typically above 600 8C), [10,11] O 6 octahedra in the ab-plane. This structural change relieves the lattice strain, as reflected by the degree of octahedral distortion (Figure 2 c, d and Table S5), and lowers the energy of the material.…”

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confidence: 99%

Low‐Temperature Cationic Rearrangement in a Bulk Metal Oxide

Retuerto

Stephens

et al. 2016

Angew Chem Int Ed

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Cationic rearrangement is a compelling strategy for producing desirable physical properties by atomic-scale manipulation. However, activating ionic diffusion typically requires high temperature, and in some cases also high pressure in bulk oxide materials. Herein, we present the cationic rearrangement in bulk Mn2 FeMoO6 at unparalleled low temperatures of 150-300 (o) C. The irreversible ionic motion at ambient pressure, as evidenced by real-time powder synchrotron X-ray and neutron diffraction, and second harmonic generation, leads to a transition from a Ni3 TeO6 -type to an ordered-ilmenite structure, and dramatic changes of the electrical and magnetic properties. This work demonstrates a remarkable cationic rearrangement, with corresponding large changes in the physical properties in a bulk oxide at unprecedented low temperatures.

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Low‐Temperature Cationic Rearrangement in a Bulk Metal Oxide

Retuerto

Stephens

et al. 2016

Angew Chem Int Ed

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“…Reconnaissance study by X-ray powder diffraction method demonstrates shrinkage of the unit cell of silician magnetites compared with normal magnetite (a 0 = 8.3970 Å; O'Neill and Dollase, 1994). Although the peaks are very diffuse due to the variation of silica contents, the specimens from the Yaguki and Tsumo mines, Nos.…”

Section: Occurrence Of Silician Magnetitesmentioning

confidence: 98%

On the Occurrence of Silician Magnetites

Shimazaki

1998

Resource Geology

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About 120 specimens of magnetite from various localities are examined by an electron microprobe analyzer. Magnetites containing more than one weight percent of silica but lack of any other components than ferrous and ferric iron, called silician magnetites in the present paper, are recognized in 23 skarn, one vein and one thermally metamorphosed massive sulfide deposits. Thus it is confirmed that this mineral occurs in nature much more frequently than so far expected. Besides silician magnetites, magnetites with appreciable amounts of Al2O3, CaO, MgO and other components along with silica, are also recognized in some skarn deposits. Magnetites with such unusual compositions are found only in hydrothermal environments, and it is suggested that precipitation mechanisms seem to be responsible for their formation.In silician magnetites, excess electric charge brought by the replacement of ferric iron in tetrahedral site by silicon, could be compensated by the replacement of ferric iron in octahedral site by ferrous iron, known as γ-Fe2SiO4 component. The natural occurrence of silician magnetites, however, gives no positive support to the existence of this component at crustal pressures. Instead a preliminary Mössbauer experiment demonstrates that one silician magnetite has a maghemite -like structure by the omission of ferrous iron from octahedral site.

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“…Depending on site occupancy, spinels are classified into three major types: normal, inverse, and random. Pirochromite MgCr 2 O 4 is classified as normal spinel with cubic crystal structure where Mg and Cr ions occupy the tetrahedral and octahedral sites; it belongs to the space group (Fd3m), with 56 atoms per unit cell (O'Neill and Dollase 1994). MgCr 2 O 4 has attracted the attention of many researchers because it could be utilized in applications such as interconnection material for solid oxide fuel cells (Schoonman et al 1991), high temperature ceramics (Kim et al 2001), humidity sensor elements (Drazic and Trontelj 1989), catalystssupport (Andrade et al 2006), strengthening agents (Hashimoto and Yamagushi 1995) and combustion catalysts (Finocchio et al 1995).…”

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confidence: 99%

Synthesis of nanostructured pirochromite magnesium chromate with egg shell membrane template

Ramachandran

Hamed

2016

Appl Nanosci

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In this work, we report on the use of fresh and boiled egg shell membrane as bio-templates in the coprecipitation of pirochromite. The structure evolution, microstructure and optical properties of the ESM templated MgCr 2 O 4 nanomaterial were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Energy dispersive X-ray spectroscopy, elemental mapping and UV-Vis-NIR spectrophotometry. The annealing of the untemplated and templated co-precipitated MgCr 2 O 4 powders at 1000°C for 4 h produced single phased nanostructured material with spinel cubic crystal structure. The FTIR results showed slight variations in the band positions m 1 and m 2 which are attributed to the change in the microstructure due to the introduction of ESM in the preparation of MgCr 2 O 4 . The morphologies and average crystallite size of the annealed MgCr 2 O 4 nanocrystalline powders depended on the type of the template. 3D hierarchical flake-like and mesh like structures were observed. The annealed MgCr 2 O 4 nanocrystalline powders have shown excitonic absorptions in the visible range 300-500 nm due to the transitions that took place from the O-2p level to the Cr-3d level. The optical band gap energies were found to be 3.68-3.71 eV for the direct band gap and 3.30-3.37 eV for the indirect band gap. This could make these MgCr 2 O 4 nanocrystalline powders possible photocatalysts in the visible range 300-500 nm.

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Crystal structures and cation distributions in simple spinels from powder XRD structural refinements: MgCr2O4, ZnCr2O4, Fe3O4 and the temperature dependence of the cation distribution in ZnAl2O4

Cited by 223 publications

References 23 publications

Low‐Temperature Cationic Rearrangement in a Bulk Metal Oxide

Low‐Temperature Cationic Rearrangement in a Bulk Metal Oxide

On the Occurrence of Silician Magnetites

Synthesis of nanostructured pirochromite magnesium chromate with egg shell membrane template

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