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Synthesis and Characterization of the Aurivillius Phase CoBi2O2F4
journal contribution
posted on 2018-07-11, 19:35 authored by Eleni Mitoudi Vagourdi, Silvia Müllner, Peter Lemmens, Reinhard K. Kremer, Mats JohnssonThe
new CoBi2O2F4 compound was
synthesized by a hydrothermal method at 230 °C. Single-crystal
X-ray diffraction data were used to determine the crystal structure.
The compound is layered and belongs to the Aurivillius family of compounds.
The present compound is the first oxo-fluoride Aurivillius phase containing
Co2+. Inclusion of a d-block cation with such a low oxidation
state as 2+ was achieved by partially replacing O2– with F– ions. The crystal structure is best described
in the tetragonal noncentrosymmetric space group I4̅ with unit-cell parameters a = 3.843(2)
Å and c = 16.341(8) Å. The crystal structure
consists of two main building units: [BiO4F4] distorted cubes and [CoF6] octahedra. Interestingly,
since the octahedra [CoF6] tilt between four equivalent
positions, the F atoms occupy a 4-fold split position at room temperature.
For the investigation of the structural disorder, Raman scattering
data were collected in the range from 10 K to room temperature. As
the temperature decreases, sharper phonon peaks appear and several
modes clearly appear, which indicates a reduction of the disorder.
Magnetic susceptibility and heat capacity measurements evidence long-range
antiferromagnetic ordering below the Néel temperature of ∼50
K. The magnetic susceptibility is in agreement with the Curie–Weiss
law above 75 K with a Curie–Weiss temperature of θCW =
−142(2) K.