Characterization of the new Bi similar to 6.2Cu similar to 6.2O8(PO4)(5) oxyphosphate; a disordered compound containing 2-and 3-O(Bi, Cu)(4) tetrahedra - wide polycationic ribbons

摘要

The present work is dedicated to the XRD, ED and HREM characterization of a new bismuth copper oxyphosphate Bisimilar to6.2Cusimilar to6.2O8(PO4)(5) (a = 11.599(2) Angstrom, b = 5.218(1) Angstrom, c = 37.541(5) Angstrom, R-1 = 0.0755, Rw(2) = 0.174, G.S Pn2(1)a). The relatively long size of its c parameter is due to the arrangement along this direction of two kinds of ribbon-like polycations formed by edge sharing O(Bi, Cu)(4) tetrahedra. The existence of such cations is characterized by the bsimilar to5.2 Angstrom value intrinsic to the ribbons structure and commonly found in bismuth oxyphosphate materials. In the title compound, 2-tetrahedra wide [Bisimilar to2.4Cusimilar to3.6O4](6.4+) and 3-tetrahedra wide [Bisimilar to5Cusimilar to3O6](9+) ribbons are isolated by phosphate groups and alternate along c. The interstitial site created between two different sizes ribbons is occupied by Cu2+ cations disordered over several close crystallographic sites. The mixed Bi3+/Cu2+ nature of certain edge-of-ribbons positions induces a disorder over several configurations of the phosphate groups. The concerned oxygen atoms form the environment of the disordered interstitial Cu2+ cations which occupy tunnels formed by the phosphate anions. The high-resolution electron microscope study enables a precise correlation between the observed images and the refined crystal structure, evidencing the polycations visualization. Furthermore, this material being the second example of partially disordered compound similar chemical system, some topological rules can be deduced. The b-axis doubling was observed by ED and HREM and is assigned to the ordering of interstitial Cu2+ within tunnels cations. A partial intra-tunnel ordering was also observed. (C) 2003 Elsevier Science (USA). All rights reserved. [References: 27]