K2FeGe3Se8: A New Antiferromagnetic Iron Selenide

A new iron selenide, K2FeGe3Se8, has been obtained by spontaneous crystallization. It adopts a new structure type in the noncentrosymmetric monoclinic space group P21. In the structure, FeSe4 and GeSe4 tetrahedra are connected alternately via corner-sharing to form one-dimensional (1D) ∞1[FeGeSe6]6– chains along the a-direction. These chains are further linked by sharing Ge2Se6 units to generate two-dimensional (2D) ∞2[FeGe3Se8]2– layers stacked parallel to the ac-plane and separated by K+ cations. Deduced from temperature-dependent susceptibility measurement and specific heat measurement under different magnetic fields, K2FeGe3Se8 exhibits an antiferromagnetic transition at ∼10 K. Furthermore, the magnetic property shows anisotropy between directions parallel and perpendicular to the plane of ∞2[FeGe3Se8]2– layer. The diffuse reflectance spectra measurement indicates that the band gap of K2FeGe3Se8 is ∼1.95(2) eV, consistent with the calculated values of 1.80 and 1.53 eV in the spin-up and spin-down directions, respectively. Based on electronic structure calculation, the spin of the Fe2+ cation is 1.85ℏ, which is comparable to the experimental value.