10.1021/cm503873x.s001
Junjie Zhang
Junjie
Zhang
Hong Zheng
Hong
Zheng
Christos
D. Malliakas
Christos
D.
Malliakas
Jared M. Allred
Jared M.
Allred
Yang Ren
Yang
Ren
Qing’an Li
Qing’an
Li
Tian-Heng Han
Tian-Heng
Han
J.F. Mitchell
J.F.
Mitchell
Brownmillerite Ca<sub>2</sub>Co<sub>2</sub>O<sub>5</sub>: Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal
Structural Transitions
American Chemical Society
2014
2Co Synthesis
specimen exhibits
neutron powder diffraction
240 K
unit cell parameters
brownmillerite form
brownmillerite structures
brownmillerite variant
Å.
Magnetic susceptibility data
Single Crystal Structural TransitionsCa 2Co
phase transitions
b axis
space group Pcmb
space groups
140 K
zone furnace
2Co crystallizes
history dependence
room temperature
2014-12-23 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Brownmillerite_Ca_sub_2_sub_Co_sub_2_sub_O_sub_5_sub_Synthesis_Stability_and_Re_entrant_Single_Crystal_to_Single_Crystal_Structural_Transitions/2222791
Ca<sub>2</sub>Co<sub>2</sub>O<sub>5</sub> 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 mm<sup>3</sup> were obtained. At room temperature,
Ca<sub>2</sub>Co<sub>2</sub>O<sub>5</sub> crystallizes as a fully
ordered brownmillerite variant in the orthorhombic space group <i>Pcmb</i> (No. 57) with unit cell parameters <i>a</i> = 5.28960(10) Å, <i>b</i> = 14.9240(2) Å, and <i>c</i> = 10.9547(2) Å. With decreasing temperature, it undergoes
a re-entrant sequence of first-order structural phase transitions
(<i>Pcmb</i> → <i>P</i>2/<i>c</i>11 → <i>P</i>12<sub>1</sub>/<i>m</i>1
→ <i>Pcmb</i>) 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 Ca<sub>2</sub>Co<sub>2</sub>O<sub>5</sub> occurs near 240 K, corroborated by neutron powder diffraction. Below
140 K, the specimen exhibits a weak ferromagnetic component directed
primarily along the <i>b</i> axis that shows a pronounced
thermal and magnetic history dependence.