Synthesis and Magnetic Properties of a Ba6Cu24– x Fe x Se27 Solid Solution with the Bartonite Structure Type

Abstract A metal selenide resulting from a mixed-site Fe/Cu solid solution was synthesized, Ba6Cu24-xFexSe27, in the composition range between Ba6Cu11Fe13Se27 (x = 13; 1) to Ba6Cu6Fe18Se27 (x = 18; 2). Its structure is derived from a parent mineral, i.e., naturally occurring bartonite K6Fe24-xS26(S,Cl), with the bartonite structure type in the I4/mmm space group and the general formula Ba6M24Se27 (M = Fe, Cu). In contrast to known low-dimensional iron selenides consisting of FeSe4 tetrahedra arranged in chains or layers, its structure is composed of a three-dimensional (3D) anionic framework of ∞3[M24Se26]10–. This 3D framework is constructed from fluorite-type clusters that link via shared-vertices. Open channels are filled by charge-compensating Ba(II) cations and isolated Se2– anions in all crystallographic directions. At the compositional end limits of the solid solution synthesized here, the Fe cations possess an average oxidation state between +2.32 in 1 and +2 in 2. Magnetic measurements reveal that 2 exhibits ferrimagnetic order at least up to 350 K, with a secondary magnetic transition at ∼170 K. In summary, these results demonstrate the utilization of a mixed Cu/Fe solid solution to stabilize a 3D metal–selenide framework, hence opening the door to wider investigations of their intriguing magnetic properties.