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Issue 5, 2002
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K1.33P4W8O32 belongs to the homologous series of monophosphate tungsten bronzes with hexagonal tunnels Ax(PO2)4(WO3)2m with 0 < x < 2 and 4 < m < 14. K1.33P4W8O32 exhibits a phase transition at Tc = 165 K, that is characterized by an anomaly in the temperature dependence of the electrical resistivity and by the occurrence of extra reflections in the X-ray scattering. Here we report the 2a × b × c superstructure at T = 120 K, as it was measured by X-ray diffraction with synchrotron radiation. The superstructure is found to be monoclinic P21 with lattice parameters a = 13.373(7) Å, b = 5.3282(1) Å, c = 8.926(4) Å, and β = 100.65°. The structure was refined within the superspace approach with superspace group P21(α, 0, γ) with α = 0.5 and γ = 0. Final agreement was obtained at R = 0.032 (R = 0.025 for the main reflections and R = 0.153 for the superstructure reflections). The maximum shift out of the average position was 0.25 Å for one of the oxygen atoms. An analysis of the displacements and variations of interatomic distances is used to show that the mechanism of the phase transition is to resolve the internal strain between the K atoms and the surrounding PO4 groups. The comparison with the CDW structure of (PO2)4(WO3)2m shows that the phase transition is not a charge-density wave, but rather that the anomaly in the resistivity is caused by the changes in the structure when going through the phase transition.

Graphical abstract: Crystal structure of monophosphate tungsten bronze K1.33P4W8O32 at 110 K

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The article was received on 01 Nov 2001, accepted on 29 Nov 2001 and first published on 21 Mar 2002

Article type: Paper
DOI: 10.1039/B109982P
J. Mater. Chem., 2002,12, 1408-1414

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    Crystal structure of monophosphate tungsten bronze K1.33P4W8O32 at 110 K

    M. Dusek, J. Lüdecke and S. van Smaalen, J. Mater. Chem., 2002, 12, 1408
    DOI: 10.1039/B109982P

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