Syntheses, Crystal Structures, Transport Properties, and Theoretical Studies of Five Members of the MAn(2)Q(5) Family: SrU2S5, BaU2Se5, PbU2S5, BaTh2S5, and BaU2Te5

International audienceFive compounds of the MAn(2)Q(5) family, namely, SrU2S5, BaU2Se5, PbU2S5, BaTh2S5, and BaU2Te5, have been synthesized by high-temperature solid-state reactions. The crystal structures of these compounds were determined by single-crystal X-ray diffraction studies. SrU2S5, BaU2Se5, PbU2S5, and BaTh2S5 crystallize in the PbU2Se5 structure type in space group C(2)h(5)P(21)/c of the monoclinic system, whereas BaU2Te5 adopts the (NH4)Pb2Br5 structure type in space group D(4)h(18)I(4/mcm) of the tetragonal system. There are no QQ bonds in these structures, so the formulas charge balance as M2+(An(2)(4+)Q(5)(2). The An atoms in the monoclinic structure are seven- or eight-coordinated by Q atoms; the U atoms in the tetragonal structure are eight-coordinated. The M atoms in the monoclinic structure are coordinated to either eight or nine Q atoms, depending on the monoclinic beta angle; the M atoms in the tetragonal structure are 10-coordinated. Resistivity studies on single crystals of SrU2S5, BaU2Se5, and PbU2S5 show metallic behavior with resistivities of 0.24, 10, and 3.3 mO.cm, respectively, at 298 K. Spin-polarized density functional theory in the generalized gradient approximation applied to the four U compounds suggests that they are ferromagnetic. In each compound, the density of states of one spin channel is found to be finite at the Fermi level, whereas there is a gap in the density of states of the other spin channel; this is characteristic of a half-metal

Syntheses, Crystal Structures, Transport Properties, and Theoretical Studies of Five Members of the MAn₂Q₅ Family: SrU₂S₅, BaU₂Se₅, PbU₂S₅, BaTh₂S₅, and BaU₂Te₅

Five compounds of the MAn₂Q₅ family, namely, SrU₂S₅, BaU₂Se₅, PbU₂S₅, BaTh₂S₅, and BaU₂Te₅, have been synthesized by high-temperature solid-state reactions. The crystal structures of these compounds were determined by single-crystal X-ray diffraction studies. SrU₂S₅, BaU₂Se₅, PbU₂S₅, and BaTh₂S₅ crystallize in the PbU₂Se₅ structure type in space group <i>C</i>_2<i>h</i>⁵–<i>P</i>2₁/<i>c</i> of the monoclinic system, whereas BaU₂Te₅ adopts the (NH₄)­Pb₂Br₅ structure type in space group <i>D</i>_4<i>h</i>¹⁸–<i>I</i>4/<i>mcm</i> of the tetragonal system. There are no Q–Q bonds in these structures, so the formulas charge balance as M²⁺(An⁴⁺)₂­(Q^2–)₅. The An atoms in the monoclinic structure are seven- or eight-coordinated by Q atoms; the U atoms in the tetragonal structure are eight-coordinated. The M atoms in the monoclinic structure are coordinated to either eight or nine Q atoms, depending on the monoclinic β angle; the M atoms in the tetragonal structure are 10-coordinated. Resistivity studies on single crystals of SrU₂S₅, BaU₂Se₅, and PbU₂S₅ show metallic behavior with resistivities of 0.24, 10, and 3.3 mΩ·cm, respectively, at 298 K. Spin-polarized density functional theory in the generalized gradient approximation applied to the four U compounds suggests that they are ferromagnetic. In each compound, the density of states of one spin channel is found to be finite at the Fermi level, whereas there is a gap in the density of states of the other spin channel; this is characteristic of a half-metal

Positional Flexibility: Syntheses and Characterization of Six Uranium Chalcogenides Related to the 2H Hexagonal Perovskite Family

International audienceSix new uranium chalcogenides, Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, Ba3MnUS6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, related to the 2H hexagonal perovskite family have been synthesized by solid-state methods at 1173 K. These isostructural compounds crystallize in the K4CdCl6 structure type in space group D-3d(6) R3 (\₎c of the trigonal system with six formula units per cell. This structure type is remarkably flexible. The structures of Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 consist of infinite (1)(infinity)[MUQ(6) (6-)] chains (M = Fe or Mn; Q = S or Se) oriented along the c axis that are separated by Ba atoms. These chains are composed of alternating M-centered octahedra and U-centered trigonal prisms sharing triangular faces; in contrast, in the structures of Ba4USe6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, there are U-centered octahedra alternating with Ba-, Rb-, or K-centered trigonal prisms. Moreover, the Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 compounds contain U4+, whereas Ba3.3Rb0.7US6 and Ba3.2K0.8US6 are mixed U4+/5+ compounds. Resistivity and mu-Raman spectroscopic measurements and DFT calculations provide additional insight into these interesting subtle structural variations