Spin glass and semiconducting behavior in one-dimensional BaFe _2-δSe ₃ (δ

We investigate the physical properties and electronic structure of BaFe _1.79(2)Se ₃ crystals, which were grown out of tellurium flux. The crystal structure of the compound, an iron-deficient derivative of the ThCr ₂Si ₂-type, is built upon edge-shared FeSe ₄ tetrahedra fused into double chains. The semiconducting BaFe _1.79(2)Se ₃ (ρ _295K = 0.18 Ω•cm and E _g = 0.30 eV) does not order magnetically; however, there is evidence for short-range magnetic correlations of spin glass type (T _f 50 K) in magnetization, heat capacity, and neutron diffraction results. A one-third substitution of selenium with sulfur leads to a slightly higher electrical conductivity (ρ _295K = 0.11 Ω•cm and E _g = 0.22 eV) and a lower spin glass freezing temperature (T _f 15 K), corroborating with higher electrical conductivity reported for BaFe ₂S ₃. According to the electronic structure calculations, BaFe ₂Se ₃ can be considered as a one-dimensional ladder structure with a weak interchain coupling.