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 1.4x0.8x0.5 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 to P2/c11 to P121/m1 to 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.

References in corpus (7)

• The nature of the magnetic order in Ca3Co2O6
• Gigantic magnetic field polarization and magnetoelectric coupling in a ferrimagnetic oxide CaBaCo4O7
• Scaling behavior in thermoelectric misfit cobalt oxides
• Slow Magnetic Order-Order Transition in the Spin Chain Antiferromagnet Ca3Co2O6
• Formation of Magnetic Microphases in Ca${}_3$Co${}_2$O${}_6$
• Structure determination of a brownmillerite Ca2Co2O5 thin film by Precession Electron Diffraction
• Re-entrant Structural Phase Transition in a Frustrated Kagome Magnet, Rb2SnCu3F12

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• Sub-nanometer depth resolution and single dopant visualization achieved by tilt-coupled multislice electron ptychography