title: Lattice-matched transition metal disulfide intergrowths: the metallic conductors Ag2Te(MS2)3 (M = V, Nb).
abstract: We present new chalcogenide compounds, Ag2Te(MS2)3 (M = V, Nb), built up of alternating planes of [MS2] and [Ag2Te]. The Ag and Te atoms are linearly coordinated by S atoms in the [MS2] layers and held in place by covalent interactions. Structural polymorphism was found by single crystal X-ray diffraction studies, where long-range ordering or disorder of the Ag and Te atoms within the hexagonal planar [Ag2Te] layer yielded two distinct crystal forms. When the Ag and Te atoms are ordered, the two isostructural compounds crystallize in the non-centrosymmetric P62m space group, with a = 5.5347(8) Å, c = 8.0248(16) Å, and V = 212.89(6) Å(3) for α-Ag2Te(VS2)3 and a = 5.7195(8) Å, c = 8.2230(16) Å, and V = 232.96(6) Å(3) for α-Ag2Te(NbS2)3. For the occupationally disordered Ag/Te arrangement, a subcell of the ordered phase that crystallizes in the non-centrosymmetric P6m2 space group, with a = 3.2956(6) Å (=a(a)/(3)(1/2)), c = 8.220(2) Å, and V = 77.31(3) Å(3) for β-Ag2Te(VS2)3, was identified. Furthermore, pair distribution function analysis revealed local distortions in the [Ag2Te] layer. Band structure calculations at the density functional theory level were carried out to investigate the electronic structure of Ag2Te(MS2)3. Electronic transport measurements on Ag2Te(MS2)3 show that they exhibit p-type metallic behavior. Thermal analyses and temperature-dependent powder X-ray diffraction studies were focused on the stability and transformation/decomposition of the Ag2Te(MS2)3 phases. Magnetic susceptibility data are also reported. The new intercalated Ag2Te(MS2)3 system features a unique hypervalent Te with a three-center, four-electron bonding environment isoelectronic to that found in I3(-).
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Sandy L
authors.initials: SL
authors.lastname: Nguyen
authors.forename: Christos D
authors.initials: CD
authors.lastname: Malliakas
authors.forename: Melanie C
authors.initials: MC
authors.lastname: Francisco
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis