Browsing by Author "Küpers, M"

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    YCa3 (CrO) 3 (BO3) 4: a Cr3+ kagomé lattice compound showing no magnetic order down to 2 K
    (American Chemical Society, 2016-07-13) Wang, CH; Avdeev, M; Kennedy, BJ; Küpers, M; Ling, CD
    We report a new gaudefroyite-type compound YCa3(CrO)3(BO3)4, in which Cr3+ ions (3d3, S = 3/2) form an undistorted kagomé lattice. Using a flux agent, the synthesis was significantly accelerated with the typical calcining time reduced from more than 2 weeks to 2 d. The structure of YCa3(CrO)3(BO3)4 was determined by combined Rietveld refinements against X-ray and neutron diffraction data. Symmetry distortion refinement starting from a disordered YCa3(MnO)3(BO3)4 model was applied to avoid overparameterization. There are two ordering models, namely, K2–1 and K2–2, with the space groups P63 (No. 173) and P3̅ (No. 147), respectively, that differ in the [BO3] ordering between different channels (in-phase or out-of-phase). Both models give similarly good fits to the diffraction data. YCa3(CrO)3(BO3)4 is an insulator with the major band gap at Eg = 1.65 eV and a second transition at 1.78 eV. Magnetically, YCa3(CrO)3(BO3)4 is dominated by anti-ferromagnetic exchange along edge-sharing CrO6 octahedral chains perpendicular to the kagomé planes, with Θ ≈ −120 K and μeff ≈ 3.92 μB. The compound shows no spin ordering or freezing down to at least 2 K. © 2016 American Chemical Society