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- Mitoudi Vagourdi, Eleni, 1988-
(författare)
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Design of new materials with crystal structure-related properties : The role of lone pair cations
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-centrosymmetry and low-dimensional arrangements, e.g. chains or layers, are very attractive structural characteristics of crystalline compounds since they are linked to some physical properties including nonlinear optical activity, ferroelectricity and magnetic frustration. The insertion of a lone-pair cation, equipped with a stereochemically active electron pair into a compound may increase its structural variety and induce the aforementioned characteristics.In this thesis some novel oxide and oxohalide compounds are described. They contain a transition metal and also a p-element lone-pair cation. Relevant synthesis details, crystal structure and physical properties of the compounds will be presented.Chemical systems containing iodate ions and either Cu2+ or Sc3+ have been explored in an effort to find new non-centrosymmetric compounds. The compounds contain also K+ due to its tendency to form highly coordinated asymmetric units. The new iodates are KCu(IO3)3 and the non-centrosymmetric compounds K3Sc(IO3)6 and KSc(IO3)3Cl.Only a few oxofluoride compounds that contain lone-pair cations have been reported in the literature, mainly due to synthetic difficulties. In this work new oxofluoride compounds containing the transition metals Cu2+, Co2+, or Sc3+ and the lone pair cations Bi3+ or Se4+ have been synthesized, where the transition metal octahedra form low-dimensional arrangements in form of chains or layers. The electronegative F ̶ anions behave like O2 ̶ and bridge in between different building blocks. The new oxofluorides are Cu2SeO3F2, CoBi2O2F4 and ScBi2O3F3. The first is a framework-like compound and the latter two are layered and belong to the Aurivillius family with one perovskite like layer. The inclusion of F made it possible to broaden this Aurivillius family to contain low-oxidation state transition metals. The magnetic properties of the new compounds containing Cu2+ and Co2+ were characterised and the Sc3+ containing non-centrosymmetric iodates were found to show non-linear optical properties.
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| 2. |
- Mitoudi Vagourdi, Eleni, 1988-, et al.
(författare)
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Synthesis and Characterization of Two New Second Harmonic Generation Active Iodates : K3Sc(IO3)6 and KSc(IO3)3Cl
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:10, s. 5235-5240
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Tidskriftsartikel (refereegranskat)abstract
- Transparent single crystals of two new iodates K3Sc(IO3)6 and KSc(IO3)3Cl have been synthesized hydrothermally. Single-crystal X-ray diffraction was used to determine their crystal structures. Both compounds crystallize in non-centrosymmetric space groups. The compound K3Sc(IO3)6 crystallizes in the orthorhombic space group Fdd2. The crystal structure is made up of [ScO6] octahedra, [IO3] trigonal pyramids, and [KO8] distorted cubes. The compound KSc(IO3)3Cl crystallizes in the trigonal space group R3. The building blocks are [ScO6] octahedra, [KO12] polyhedra, and [IO3] trigonal pyramids. The Cl– ions act as counter ions and reside in tunnels in the crystal structure. The second harmonic generation (SHG) measurements at room temperature, using 1064 nm radiation, on polycrystalline samples show that the SHG intensities of K3Sc(IO3)6 and KSc(IO3)3Cl are around 2.8 and 2.5 times that of KH2PO4 (KDP), respectively. In addition, K3Sc(IO3)6 and KSc(IO3)3Cl are phase-matchable at the fundamental wavelength of 1064 nm. The large anharmonicity in the optical response of both compounds is further supported by an anomalous temperature dependence of optical phonon frequencies as well as their enlarged intensities in Raman scattering. The latter corresponds to a very large electronic polarizability.
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| 3. |
- Scott, E. A. S., et al.
(författare)
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Bi2CoO2F4─A Polar, Ferrimagnetic Aurivillius Oxide-Fluoride
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:21, s. 9775-9785
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Tidskriftsartikel (refereegranskat)abstract
- Aurivillius oxides have been a research focus due to their ferroelectric properties, but by replacing oxide ions by fluoride, divalent magnetic cations can be introduced, giving Bi2MO2F4(M = Fe, Co, and Ni). Our combined experimental and computational study on Bi2CoO2F4 indicates a low-temperature polar structure of P21ab symmetry (analogous to ferroelectric Bi2WO6) and a ferrimagnetic ground state. These results highlight the potential of Aurivillius oxide-fluorides for multiferroic properties. Our research has also revealed some challenges associated with the reduced tendency for polar displacements in the more ionic fluoride-based systems.
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