The vanadium oxide bronze Cu2.33-xV4O11. Solid state chemistry, XRD

Solid state chemistry of the vanadium oxide bronze (VOB) Cu2.33-xV4O11 show s that at 600 degreesC the synthesis in both Cu2O or CuO-V2O5-V2O4 systems leads to the conclusion that the homogeneity range is rather narrow (0 less than or equal to x < 0.08). The Cu2.33-xV4O11 average structure shows that this phase crystallizes in the monoclinic system, space group Cm with the cell parameters a = 15.309(3); b = 3.610(1); c = 7.335(2) <Angstrom>; beta = 101.84(1)degrees with Z = 4 unit formula. The detailed description of the structure is reported. The copper ions lie between [V(4)O1(11)](n) layers built up of VO6, octahedra. Cu ions exhibit non usual tetrahedral coordinat ion and CN = 3 + 2 polyhedra making the estimation of the electric balance between the couples Cu+-Cu2+ and V4+-V5+ difficult. A superstructure, which also exists at low temperature, is shown at room temperature by Bragg and Weissenberg diagrams. The homogeneity range of this VOB is discussed in lig ht of its structural features. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.