Synthesis and Characterization of Two Quaternary Uranium Tellurides, RbTiU3Te9 and CsTiU3Te9

Black crystals of RbTiU3Te9 and CsTiU3Te9 have been synthesized at 1223 and 1173 K, respectively, by high-temperature solid-state routes. These compounds crystallize in a new structure type in space group C2h2-P21/m of the monoclinic system. The structure, which is similar to that of CsTiUTe5, consists of UTe2 layers connected into a three-dimensional framework by TiTe6 octahedra. The expanded UTe2 layers leave channels that are filled by Rb or Cs atoms. Single-crystal resistivity measurements on CsTiU3Te9 are consistent with semiconducting behavior; the calculated activation energy is 0.30(1) eV. X-ray photoelectron spectroscopic measurements on CsTiU3Te9 indicate that the compound contains U4+. From single-crystal magnetic measurements, CsTiU3Te9 is consistent with antiferromagnetic coupling between magnetic U atoms. The very low value of the effective magnetic moment of 0.56(2) μB is believed to arise from a coexistence of magnetic and nonmagnetic U atoms.