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  • 1.
    Mitoudi Vagourdi, Eleni
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Müllner, Silvia
    Lemmens, Peter
    Kremer, Reinhard K.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and Characterization of the Aurivillius Phase CoBi2O2F42018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 15, p. 9115-9121Article in journal (Refereed)
    Abstract [en]

    The new CoBi2O2F4 compound was synthesized by a hydrothermal method at 230 degrees 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 I<(4)overbar> with unit-cell parameters a = 3.843(2) angstrom and c = 16.341(8) angstrom. 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 Neel temperature of similar to 50 K. The magnetic susceptibility is in agreement with the Curie-Weiss law above 75 K with a Curie-Weiss temperature of theta(cw) = -142(2) K.

  • 2.
    Mitoudi Vagourdi, Eleni
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhang, Weiguo
    Denisova, Ksenia
    Lemmens, Peter
    Halasyamani, Shiv
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and Characterization of two new SHG active iodates: K3Sc(IO3)6 and KSc(IO3)3ClIn: ACS Omega, E-ISSN 2470-1343Article in journal (Refereed)
  • 3.
    Mitoudi-Vagourdi, Eleni
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Papawassiliou, Wassilios
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Müllner, Silvia
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Pell, Andrew J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lemmens, Peter
    Kremer, Reinhard K.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and Physical Properties of the Oxofluoride Cu-2(SeO3)F-22018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 8, p. 4640-4648Article in journal (Refereed)
    Abstract [en]

    Single crystals of the new compound Cu-2(SeO3)F-2 were successfully synthesized via a hydrothermal method, and the crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma with the unit cell parameters a = 7.066(4) (A) over circle, b = 9.590(4) (A) over circle, and c = 5.563(3) (A) over circle. Cu-2(SeO3)F-2 is isostructural with the previously described compounds Co2TeO3F2 and CoSeO3F2. The crystal structure comprises a framework of corner- and edge-sharing distorted [CuO3F3] octahedra, within which [SeO3] trigonal pyramids are present in voids and are connected to [CuO3F3] octahedra by corner sharing. The presence of a single local environment in both the F-19 and Se-77 solid-state MAS NMR spectra supports the hypothesis that O and F do not mix at the same crystallographic positions. Also the specific phonon modes observed with Raman scattering support the coordination around the cations. At high temperatures the magnetic susceptibility follows the Curie-Weiss law with Curie temperature of Theta = -173(2) K and an effective magnetic moment of mu(eff) similar to 2.2 mu(B). Antiferromagnetic ordering below similar to 44 K is indicated by a peak in the magnetic susceptibility. A second though smaller peak at similar to 16 K is tentatively ascribed to a magnetic reorientation transition. Both transitions are also confirmed by heat capacity measurements. Raman scattering experiments propose a structural phase instability in the temperature range 6-50 K based on phonon anomalies. Further changes in the Raman shift of modes at similar to 46 K and similar to 16 K arise from transitions of the magnetic lattice in accordance with the susceptibility and heat capacity measurements.

  • 4.
    Mitoudi-Vagourdi, Eleni
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rienmüller, Julia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lemmens, Peter
    Gnezdilov, Vladimir
    Kremer, Reinhard K.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and Magnetic Properties of the KCu(IO3)(3) Compound with [CuO5](infinity) Chains2019In: Acs Omega, ISSN 2470-1343, Vol. 4, no 12, p. 15168-15174Article in journal (Refereed)
    Abstract [en]

    The new quaternary iodate KCu(IO3)(3) has been prepared by hydrothermal synthesis. KCu(IO3)(3) crystallizes in the monoclinic space group P2(1)/n with unit cell parameters a = 9.8143(4) angstrom, b = 8.2265(4) angstrom, c = 10.8584(5) angstrom,beta = 91.077(2)degrees, and z = 4. The crystals are light blue and translucent. There are three main building units making up the crystal structure: [KO10] irregular polyhedra, [CuO6] distorted octahedra, and [IO3] trigonal pyramids. The Jahn-Teller elongated [CuO6] octahedra connect to each other via corner sharing to form [CuO5](infinity) zigzag chains along [010]; the other building blocks separate these chains. The Raman modes can be divided into four groups; the lower two groups into mainly lattice modes involving K and Cu displacements and the upper two groups into mainly bending and stretching modes of [IO3E], where E represents a lone pair of electron. At low temperatures, the magnetic susceptibility is characterized by a broad maximum centered at similar to 5.4 K, characteristic for antiferromagnetic short-range ordering. Long-range magnetic ordering at T-C = 1.32 K is clearly evidenced by a sharp anomaly in the heat capacity. The magnetic susceptibility can be very well described by a spin S = 1/2 antiferromagnetic Heisenberg chain with a nearest-neighbor spin exchange of similar to 8.9 K.

  • 5.
    Yu, Xiaowen
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mitoudi-Vagourdi, Eleni
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The Aurivillius Compound CoBi2O2F4 - an Efficient Catalyst for Electrolytic Water Oxidation after Liquid Exfoliation2019In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 11, no 24, p. 6105-6110Article in journal (Refereed)
    Abstract [en]

    Investigation of new high-efficiency catalysts for the oxygen evolution reaction (OER) is important for propelling the practical applications of water splitting. Here we report the Aurivillius compound CoBi2O2F4 to be a novel catalyst for catalytic OER. After liquid exfoliation of CoBi2O2F4 crystals in isopropanol, the resulting thin sheets deliver a low overpotential of 334 mV and a small Tafel slope of 47 mV dec(-1) for catalytic OER, exhibiting substantially higher activity and faster kinetics compared with as-synthesized crystals. This attributes to the increase in accessible surface area and dangling bonds on the edges providing more active sites exposed on the surface after exfoliation. The positive effects of F- anions to benefit OH- adsorption/combination and p-block Bi3+ cations to direct reactants to preferred sites are proposed to synergistically improve the Co-active centers for catalysis; based on this, the OER reaction mechanism on this new catalyst is discussed.

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