Bidimensional cationic ordering and thermal dependence in {beta}-Pb{sub x}V{sub 2}O{sub 5} bronzes
- Univ. des Sciences et Technologies de Lille, Villeneuve d`Ascq (France). Lab. de Cristallochimie et Physicochimie du Solide
The monoclinic lead vanadium oxide bronzes {beta}-Pb{sub x}V{sub 2}O{sub 5} were investigated for their cationic ordering within the host lattice. Superstructure reflections appear on X-ray powder patterns beyond x {approx} 0.30. For the formal x = 0.30 lead radio, the crystal structure was refined from X-ray single crystal data in the (a, 2b, c) unit cell, a = 15.478(10) {angstrom}, 2b = 7.288(5) {angstrom}, c = 10.123(6) {angstrom}, {beta} = 109.29(1){degree}, S. G. P2{sub 1}/m and final R = 0.047, R{sub w} = 0.054. It shows evidence of an intratunnel ordering involving a Pb{sup 2+} zigzag sequence running parallel to the b axis while ordered and disordered tunnels alternate along the a axis. Pb{sup 2+} display different interaction with the V-O framework according to the kind of tunnels it occupies. Electron diffraction patterns confirmed the X-ray results. A supplementary 2a periodicity was sometimes observed in small crystals as a subcondition of the previous ordering. Weissenberg photographs and electronic diffraction patterns allowed the proposition of a bidimensional cationic ordering model in the fourfold (2a, 2b, c) unit cell. In that case, the intertunnel ordering involves strong local Pb{sup 2+} electrostatic effects despite the shielding of the tunnel walls. The thermal analysis (DTA and high temperature electronic microscopy) evidenced the irreversible disappearing of the superstructure on heating while a second rearrangement is observed on cooling. 28 refs., 12 figs., 5 tabs.
- OSTI ID:
- 679229
- Journal Information:
- Journal of Solid State Chemistry, Vol. 145, Issue 1; Other Information: PBD: Jun 1999
- Country of Publication:
- United States
- Language:
- English
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