Naveed Zafar Ali

Publications (3)6.89 Total impact

• Article: CsCoO(2) Featuring a Novel Polyoxocobaltate(III) Anion Based on a Two-Dimensional Architecture of Interconnected Tetrahedra.

  Naveed Zafar Ali, Jürgen Nuss, Reinhard K Kremer, Martin Jansen
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  ABSTRACT: CsCoO(2) has been prepared along the azide/nitrate route as a reddish black microcrystalline powder at 833 K. According to single crystal X-ray analysis, the title compound crystallizes as a structure type novel for oxides (Cmca,Z = 8, a = 5.9841(1) Å, b = 12.2458(2) Å, c = 8.2650(1) Å). The prominent features of the structure are pairs of edge-linked CoO(4) tetrahedra to form Co(2)O(6) dimers, which are condensed by vertex sharing of the four remaining unshared oxygen atoms to form a two-dimensional architecture of a puckered polyoxyanion spreading along (010). Upon cooling, CsCoO(2) undergoes a virtually second order phase transition at ∼100 K leading to a systematic dovetail twin (C2/c). The magnetic susceptibilities show the dominance of antiferromagnetic interactions with a remarkably high Néel temperature of 430 K indicating a very strong antiferromagnetic superexchange between the Co(3+) ions. The spin-exchange for CsCoO(2) can be addressed as a set of strongly antiferromagnetically coupled quasi-one-dimensional chains, which are weakly coupled to neighboring chains by ferromagnetic interaction.
  Inorganic Chemistry 10/2012; · 4.60 Impact Factor
• Article: Spin exchange dominated by charge fluctuations of the Wigner lattice in the chain cuprate Na(5)Cu(3)O(6)

  Naveed Zafar Ali, Jesko Sirker, Juergen Nuss, Peter Horsch, Martin Jansen
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  ABSTRACT: Na5Cu3O6, a new member of one-dimensional charge-ordered chain cuprates, was synthesized via the azide/nitrate route by reacting NaN3, NaNO3, and CuO. According to single-crystal x-ray analysis, one-dimensional ∞ 1CuO2n- chains built up from planar, edge-sharing CuO4 squares are a dominant feature of the crystal structure. From the analysis of the Cu-O bond lengths, we find that the system forms a Wigner lattice. The commensurate charge order allows the explicit assignment of the valence states of either +2 or +3 to each copper atom, resulting in a repetition according to Cu2+-Cu3+-Cu2+-Cu2+-Cu3+-Cu2+. Following the theoretical analysis of the previously synthesized compounds Na3Cu2O4 and Na8Cu5O10, the magnetic susceptibility was expected to show a large dimer gap. Surprisingly, this is not the case. To resolve this puzzle, we show that the magnetic couplings in this compound are strongly affected by excitations across the Wigner charge gap. By including these contributions, which are distinct from conventional superexchange in Mott-insulators, we obtain a quantitatively satisfying theoretical description of the magnetic susceptibility data.
  Physical Review B. 07/2011; 84:035113.
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  Available from: mpg.de

  Article: Structure of RbFeO2, refined from a reticular pseudomerohedrally twinned crystal with six domains.

  Jürgen Nuss, Naveed Zafar Ali, Martin Jansen
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  ABSTRACT: RbFeO(2), rubidium oxoferrate, crystallizes as an orthorhombic structure. The crystals under investigation were composed of six individuals representing reticular pseudomerohedral twins with a pseudocubic twin lattice of index 4 because of the approximate equations a(8)(1/2) = b(2)(1/2) = c. The compound is isostructural with KFeO(2) (KGaO(2) type of structure) and is composed of [FeO(4/2)](-) corner-sharing tetrahedra, forming a three-dimensional cristobalite-like network, with Rb(+) ions occupying its interstices.
  Acta Crystallographica Section B Structural Science 11/2007; 63(Pt 5):719-25. · 2.29 Impact Factor