Hard–soft synthesis of a new series of vacancy-ordered perovskites, CaCrO<sub>3−δ</sub>

Arévalo‐López, Ángel M.; Liang, Bing; Senn, Mark S.; Murray, Claire; Tang, Chiu C.; Attfield, J. Paul

doi:10.1039/c4tc01808g

Cited by 14 publications

(24 citation statements)

References 15 publications

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“…This structure was previously refined against X-ray data in the aristotype Imma brownmillerite structure, in which the tetrahedral are disordered. 7 Ordered tilts of the tetrahedra can give rise to low symmetry superstructures, 13 as found in other reported Ca 2 M 2 O 5 brownmillerites at room temperature. Ca 2 Fe 2 O 5 has a Pnma superstructure 14 17 Fits of the two simple ordering models to the 300 K profile of Ca 2 Cr 2 O 5 gave a slightly better goodness-of-fit χ 2 = 1.63 for I2mb than for Pnma where χ 2 = 1.69, and no breaking of the body-centring reflection condition was observed.…”

Section: Crystal Structurementioning

confidence: 54%

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

Arévalo‐López

Attfield

2015

Dalton Trans.

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Powder neutron diffraction and magnetic susceptibility measurements at 10-300 K have been used to determine the crystal and magnetic structures of brownmillerite type Ca(2)Cr(2)O(5), which was obtained by reduction of the high pressure phase CaCrO(3) through hard-soft chemistry. The ambient temperature crystal structure of Ca(2)Cr(2)O(5) is refined in space group I2mb and the unusual tetrahedral coordination of Cr(3+) results in local structural distortions. Cr(3+) spins order antiferromagnetically below 220 K and a substantial observed canting of moments shows that Heisenberg exchange is weak or frustrated and competes with antisymmetric Dzialoshinskii-Moriya interactions.

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Section: Crystal Structurementioning

confidence: 54%

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

Arévalo‐López

Attfield

2015

Dalton Trans.

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“…[8] The hard-soft route was also used to discover three new reduced CaCrO 3-δ ( = 0.33, 0.4 and 0.5) phases. [9] The most reduced phase, Ca 2 Cr 2 O 5 , is an unusual Cr 3+ brownmillerite structure with antiferromagnetic order at 220 K and a substantial canting of ordered moments. [10] The above ACrO 3 (A = Ca, Sr) precursor perovskites are only formed in a cubic-type (3C) polytype at moderate pressures, but a variety of hexagonal perovskite polytypes are known for the A = Ba analogue.…”

Section: Introductionmentioning

confidence: 99%

High-pressure BaCrO3 polytypes and the 5H–BaCrO2.8 phase

Arévalo‐López

Attfield

2015

Journal of Solid State Chemistry

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Cite this article as: Angel M. Arévalo-López and J. Paul Attfield, High-pressure BaCrO 3 polytypes and the 5H-BaCrO 2.8 phase, Journal of Solid State Chemistry, http://dx. AbstractPolytypism of BaCrO 3 perovskites has been investigated at 900-1100 °C and pressures up to 22 GPa.Hexagonal 5H, 4H, and 6H perovskites are observed with increasing pressure, and the cubic 3C perovskite (a = 3.99503(1) Å) is observed in bulk form for the first time at 19-22 GPa. An oxygendeficient material with limiting composition 5H-BaCrO 2.8 is synthesised at 1200 °C under ambient pressure. This contains double tetrahedral Cr 4+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure.

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“…While in most cases the refinement of superstructures is achieved using X‐ray, neutron or electron diffraction techniques that provide average structural information in the reciprocal space, direct observations of superstructures at atomic resolution are possible via the negative spherical aberration imaging technique, and the combined application of high‐angle annular‐dark‐field (HAADF) electron microscopy and core‐level spectroscopy …”

Section: Introductionmentioning

confidence: 99%

Atomic‐Scale Study of Cation Ordering in Potassium Tungsten Bronze Nanosheets

Jiang

et al. 2017

Advanced Science

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It has long been accepted that the formation of superlattices in hexagonal‐based potassium tungsten bronzes is attributed to K vacancies only, together with small displacements of W cations. Here, the superlattices within potassium tungsten bronze nanosheets both structurally and spectroscopically at atomic resolution using comprehensive transmission electron microscopy techniques are studied. The multidimensional chemical analyses are realized by energy‐dispersive X‐ray spectroscopy, electron energy‐loss spectroscopy, and X‐ray photoelectron spectroscopy, the atomic‐scale structures are characterized using aberration‐corrected scanning transmission electron microscopy with high‐angle annular‐dark‐field detector. The observed superstructures are mainly attributed to small amount of W vacancies within single atomic layer, which would recover to more uniform distributions of W vacancies with lower concentrations at higher temperature. The band regions of different orientation from the matrix tend to regulate the superstructures to be pinned along the same direction, forming domains of highly ordered structures. The characterization of cation ordering and recovery processes of nanostructures from chemical and structural point of view at atomic resolution enables rational design of optoelectronic devices with controlled physical properties.

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Hard–soft synthesis of a new series of vacancy-ordered perovskites, CaCrO_3−δ

Cited by 14 publications

References 15 publications

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

High-pressure BaCrO3 polytypes and the 5H–BaCrO2.8 phase

Atomic‐Scale Study of Cation Ordering in Potassium Tungsten Bronze Nanosheets

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Hard–soft synthesis of a new series of vacancy-ordered perovskites, CaCrO3−δ

Cited by 14 publications

References 15 publications

Crystal and magnetic structures of the brownmillerite Ca2Cr2O5

Crystal and magnetic structures of the brownmillerite Ca2Cr2O5

High-pressure BaCrO3 polytypes and the 5H–BaCrO2.8 phase

Atomic‐Scale Study of Cation Ordering in Potassium Tungsten Bronze Nanosheets

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Product

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Hard–soft synthesis of a new series of vacancy-ordered perovskites, CaCrO_3−δ

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅

Crystal and magnetic structures of the brownmillerite Ca₂Cr₂O₅