title: Syntheses and characterization of six quaternary uranium chalcogenides A2M4U6Q17 (A = Rb or Cs; M = Pd or Pt; Q = S or Se).
abstract: The A(2)M(4)U(6)Q(17) compounds Rb(2)Pd(4)U(6)S(17), Rb(2)Pd(4)U(6)Se(17), Rb(2)Pt(4)U(6)Se(17), Cs(2)Pd(4)U(6)S(17), Cs(2)Pd(4)U(6)Se(17), and Cs(2)Pt(4)U(6)Se(17) were synthesized by the high-temperature solid-state reactions of U, M, and Q in a flux of ACl or Rb(2)S(3). These isostructural compounds crystallize in a new structure type, with two formula units in the tetragonal space group P4/mnc. This structure consists of a network of square-planar MQ(4), monocapped trigonal-prismatic UQ(7), and square-antiprismatic UQ(8) polyhedra with A atoms in the voids. Rb(2)Pd(4)U(6)S(17) is a typical semiconductor, as deduced from electrical resistivity measurements. Magnetic susceptibility and specific heat measurements on single crystals of Rb(2)Pd(4)U(6)S(17) show a phase transition at 13 K, the result either of antiferromagnetic ordering or of a structural phase transition. Periodic spin-polarized band structure calculations were performed on Rb(2)Pd(4)U(6)S(17) with the use of the first principles DFT program VASP. Magnetic calculations included spin-orbit coupling. With U f-f correlations taken into account within the GGA+U formalism in calculating partial densities of states, the compound is predicted to be a narrow-band semiconductor with the smallest indirect and direct band gaps being 0.79 and 0.91 eV, respectively.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
authors.forename: George N
authors.initials: GN
authors.lastname: Oh
authors.forename: Eun Sang
authors.initials: ES
authors.lastname: Choi
authors.forename: Jun
authors.initials: J
authors.lastname: Lu
authors.forename: Lukasz A
authors.initials: LA
authors.lastname: Koscielski
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Ward
authors.forename: Donald E
authors.initials: DE
authors.lastname: Ellis
authors.forename: James A
authors.initials: JA
authors.lastname: Ibers