YCa3(CrO)3(BO3)4: a Cr3+ kagomé lattice compound showing no magnetic order down to 2 K

Abstract

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 two weeks to two days. 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 over-parameterization. There are two ordering models, K2-1 and K2-2 with the space groups P63 (#173) and (#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 = 1.65eV and a second transition at 1.78 eV. Magnetically, YCa3(CrO)3(BO3)4 is dominated by antiferromagnetic 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 observed down to at least 2 K.