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New metal-rich mixed chalcogenides with intergrowth structures: Ni8.21Ge2S2 and Ni8.45Ge2Se2

2009; Elsevier BV; Volume: 11; Issue: 6 Linguagem: Inglês

10.1016/j.solidstatesciences.2009.03.005

1873-3085

Anna Isaeva, A. I. Baranov, Lars Kloo, Michael Ruck, B. A. Popovkin,

Rare-earth and actinide compounds

Abstract New metal-rich mixed nickel germanium chalcogenides, Ni8.21(1)Ge2S2 and Ni8.45(1)Ge2Se2, were synthesized by a high-temperature ceramic technique. Ni8.21Ge2S2 decomposes incongruently at 798(5) °C, while Ni8.45Ge2Se2 is stable only between approximately 600(5) °C and 813(5) °C. Single crystals were grown from a molten flux and by a recrystallization of presynthesized charge. The X-ray diffraction study revealed that Ni8.21Ge2S2 and Ni8.45Ge2Se2 are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2) with a = 3.578(1) A, c = 24.687(5) A, and a = 3.601(1) A, c = 25.427(6) A, respectively. Their crystal structures comprise heterometallic [ Ni 6 Ge 2 ] ∞ 2 slabs and are closely related to the Ni8.54Ga2Se2 and Ni8.93Sn2S2 structure types. The geometrical changes of structural units upon p-element substitution in all known Ni10−δE2Q2 (E = element of group 13 or 14; Q = chalcogen) compounds are discussed. The relation to the intergrowth structure of Ni5.46GeSe2 is analyzed.