Synthesis and characterization of the new uranium yttrium oxysulfide UY₄O₃S₅

Red needles of UY₄O₃S₅ have been synthesized by the solid-state reaction at 1273 K of UOS and Y₂S₃ with Sb₂S₃ as a flux. UY₄O₃S₅ adopts a three-dimensional structure that contains five crystallographically unique heavy-atom positions. U and Y atoms disorder on one eight-coordinate metal position bonded to four O atoms and four S atoms and two seven-coordinate metal positions bonded to three O atoms and four S atoms. Another eight-coordinate metal position with two O and six S atoms and one six-coordinate metal position with six S atoms are exclusively occupied by Y atoms. UY₄O₃S₅ is a modified Curie-Weiss paramagnet between 1.8 and 300 K. Its effective magnetic moment is estimated to be 3.3(2) μ_B. UY₄O₃S₅ has a band gap of 1.95 eV. The electrical resistivity along the [010] direction of a single crystal shows Arrhenius-type thermal activation with an activation energy of 0.2 eV.