Synthesis, structure, and electrical resistivity of Cs3U18Se38

Cs3U18Se38 was synthesized by the solid-state reactions of U, Se, CsCl or Cs2Se3, and P or As at 1273 K. This compound crystallizes in a new structure in the tetragonal space group D184h-I4/mcm. The asymmetric unit contains U atoms in four different coordination environments. The overall three-dimensional network structure contains channels along the c axis, in which the Cs atoms lie. The formula Cs3U18Se38 does not charge balance with the typical formal oxidation states of the elements. Electrical resistivity measurements conducted on a single crystal reveal a broad feature at 225 K, atypical semiconductor behavior below 57 K, and a calculated band gap of 0.0030(1) eV.