Synthesis and Characterization of the Aurivillius Phase CoBi2O2F4

• Published in: Inorganic chemistry 2018-08, Vol.57 (15), p.9115-9121
• Main Authors: Mitoudi Vagourdi, Eleni, Müllner, Silvia, Lemmens, Peter, Kremer, Reinhard K, Johnsson, Mats
• Format: Article
• Language: English
• Subjects: Inorganic Chemistry; oorganisk kemi
• ISSN: 0020-1669; 1520-510X; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b01118

The 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.