Brownmillerite Ca2Co2O5: Synthesis, stability, and re-entrant single crystal to single crystal structural transitions

Junjie Zhang; Hong Zheng; Christos D. Malliakas; Jared M. Allred; Yang Ren; Qing'An Li; Tian-Heng Han; J. F. Mitchell

doi:10.1021/cm503873x

Brownmillerite Ca₂Co₂O₅: Synthesis, stability, and re-entrant single crystal to single crystal structural transitions

Junjie Zhang^*, Hong Zheng, Christos D. Malliakas, Jared M. Allred, Yang Ren, Qing'An Li, Tian-Heng Han, J. F. Mitchell

^*Corresponding author for this work

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

41 Citations (Scopus)

Abstract

Ca₂Co₂O₅ in the brownmillerite form was synthesized using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4 × 0.8 × 0.5 mm³ were obtained. At room temperature, Ca₂Co₂O₅ crystallizes as a fully ordered brownmillerite variant in the orthorhombic space group Pcmb (No. 57) with unit cell parameters a = 5.28960(10) Å, b = 14.9240(2) Å, and c = 10.9547(2) Å. With decreasing temperature, it undergoes a re-entrant sequence of first-order structural phase transitions (Pcmb → P2/c11 → P12₁/m1 → Pcmb) that is unprecedented among brownmillerites, broadening the family of space groups available to these materials and challenging current approaches for sorting the myriad variants of brownmillerite structures. Magnetic susceptibility data indicate antiferromagnetic ordering in Ca₂Co₂O₅ occurs near 240 K, corroborated by neutron powder diffraction. Below 140 K, the specimen exhibits a weak ferromagnetic component directed primarily along the b axis that shows a pronounced thermal and magnetic history dependence.

Original language	English
Pages (from-to)	7172-7182
Journal	Chemistry of Materials
Volume	26
Issue number	24
DOIs	https://doi.org/10.1021/cm503873x
Publication status	Published - 23 Dec 2014
Externally published	Yes

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@article{7fb87719cd1c443c8e220f28d9a70dce,

title = "Brownmillerite Ca2Co2O5: Synthesis, stability, and re-entrant single crystal to single crystal structural transitions",

abstract = "Ca2Co2O5 in the brownmillerite form was synthesized using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4 × 0.8 × 0.5 mm3 were obtained. At room temperature, Ca2Co2O5 crystallizes as a fully ordered brownmillerite variant in the orthorhombic space group Pcmb (No. 57) with unit cell parameters a = 5.28960(10) {\AA}, b = 14.9240(2) {\AA}, and c = 10.9547(2) {\AA}. With decreasing temperature, it undergoes a re-entrant sequence of first-order structural phase transitions (Pcmb → P2/c11 → P121/m1 → Pcmb) that is unprecedented among brownmillerites, broadening the family of space groups available to these materials and challenging current approaches for sorting the myriad variants of brownmillerite structures. Magnetic susceptibility data indicate antiferromagnetic ordering in Ca2Co2O5 occurs near 240 K, corroborated by neutron powder diffraction. Below 140 K, the specimen exhibits a weak ferromagnetic component directed primarily along the b axis that shows a pronounced thermal and magnetic history dependence.",

author = "Junjie Zhang and Hong Zheng and Malliakas, {Christos D.} and Allred, {Jared M.} and Yang Ren and Qing'An Li and Tian-Heng Han and Mitchell, {J. F.}",

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TY - JOUR

T1 - Brownmillerite Ca2Co2O5

T2 - Synthesis, stability, and re-entrant single crystal to single crystal structural transitions

AU - Zhang, Junjie

AU - Zheng, Hong

AU - Malliakas, Christos D.

AU - Allred, Jared M.

AU - Ren, Yang

AU - Li, Qing'An

AU - Han, Tian-Heng

AU - Mitchell, J. F.

N1 - Publication details (e.g. title, author(s), publication statuses and dates) are captured on an “AS IS” and “AS AVAILABLE” basis at the time of record harvesting from the data source. Suggestions for further amendments or supplementary information can be sent to [email protected].

PY - 2014/12/23

Y1 - 2014/12/23

N2 - Ca2Co2O5 in the brownmillerite form was synthesized using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4 × 0.8 × 0.5 mm3 were obtained. At room temperature, Ca2Co2O5 crystallizes as a fully ordered brownmillerite variant in the orthorhombic space group Pcmb (No. 57) with unit cell parameters a = 5.28960(10) Å, b = 14.9240(2) Å, and c = 10.9547(2) Å. With decreasing temperature, it undergoes a re-entrant sequence of first-order structural phase transitions (Pcmb → P2/c11 → P121/m1 → Pcmb) that is unprecedented among brownmillerites, broadening the family of space groups available to these materials and challenging current approaches for sorting the myriad variants of brownmillerite structures. Magnetic susceptibility data indicate antiferromagnetic ordering in Ca2Co2O5 occurs near 240 K, corroborated by neutron powder diffraction. Below 140 K, the specimen exhibits a weak ferromagnetic component directed primarily along the b axis that shows a pronounced thermal and magnetic history dependence.

AB - Ca2Co2O5 in the brownmillerite form was synthesized using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4 × 0.8 × 0.5 mm3 were obtained. At room temperature, Ca2Co2O5 crystallizes as a fully ordered brownmillerite variant in the orthorhombic space group Pcmb (No. 57) with unit cell parameters a = 5.28960(10) Å, b = 14.9240(2) Å, and c = 10.9547(2) Å. With decreasing temperature, it undergoes a re-entrant sequence of first-order structural phase transitions (Pcmb → P2/c11 → P121/m1 → Pcmb) that is unprecedented among brownmillerites, broadening the family of space groups available to these materials and challenging current approaches for sorting the myriad variants of brownmillerite structures. Magnetic susceptibility data indicate antiferromagnetic ordering in Ca2Co2O5 occurs near 240 K, corroborated by neutron powder diffraction. Below 140 K, the specimen exhibits a weak ferromagnetic component directed primarily along the b axis that shows a pronounced thermal and magnetic history dependence.

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DO - 10.1021/cm503873x

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