Synthesis, crystal structure and physical properties of FeV4S8 and KFe2V8S16

Abstract

Two compounds with the formulae FeV₄S₈ and KFe₂V₈S₁₆ were successfully synthesized via a melting salt method. The FeV₄S₈ crystallizes in the defective NiAs-like structure type of a monoclinic I2/m space group, while the KFe₂V₈S₁₆ belongs to the pseudo-hollandite chalcogenide family and crystallizes in a monoclinic C2/m space group. The structure of the FeV₄S₈ is composed of [V₄S₈]³⁻ layers which are connected by [FeS₆]⁹⁻ octahedra to form a 3D extended framework. The structure of KFe₂V₈S₁₆ is composed of a [Fe₂V₈S₁₆]⁻ one-dimensional (1D) tunnel-type framework, where the Fe atoms partially occupy the V1 site. In the KFe₂V₈S₁₆ compound, the K⁺ ions reside in the tunnels. Magnetic measurements show that the two compounds are both paramagnetic at high temperature. Weak ferromagnetic contributions are observed at low temperature for both of the compounds. The resistivity of FeV₄S₈ is measured to be 5.1 × 10⁻² Ω cm at room temperature. With the decrease in temperature, the compound shows a clear metal-to-insulator phase transition at 163 K.