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Syntheses and Characterization of Six Quaternary Uranium Chalcogenides A2M4U6Q17 (A = Rb or Cs; M = Pd or Pt; Q = S or Se)

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posted on 20.08.2012, 00:00 by George N. Oh, Eun Sang Choi, Jun Lu, Lukasz A. Koscielski, Matthew D. Ward, Donald E. Ellis, James A. Ibers
The A2M4U6Q17 compounds Rb2Pd4U6S17, Rb2Pd4U6Se17, Rb2Pt4U6Se17, Cs2Pd4U6S17, Cs2Pd4U6Se17, and Cs2Pt4U6Se17 were synthesized by the high-temperature solid-state reactions of U, M, and Q in a flux of ACl or Rb2S3. 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 MQ4, monocapped trigonal-prismatic UQ7, and square-antiprismatic UQ8 polyhedra with A atoms in the voids. Rb2Pd4U6S17 is a typical semiconductor, as deduced from electrical resistivity measurements. Magnetic susceptibility and specific heat measurements on single crystals of Rb2Pd4U6S17 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 Rb2Pd4U6S17 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.