The vanadium oxide bronze Cu_(2.33 -x)V_4O_(11). Solid state chemistry, XRD

摘要

Solid state chemistry of the vanadium oxide bronze (VOB) Cu_(2.33 -x)V_4O_(11) shows that at 600 deg C the synthesis in both Cu_2O or CuO-V_2O_5-V_2O_4 systems leads to the conclusion that the homogeneity range is rather narrow (0 <= X <0.08). The Cu_(2.33 -x)V_4O_(11) 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) A; #beta# = 101.84(1) deg with Z = 4 unit formula. The detailed description of the structure is reported. The copper ions lie between (V_4O_(11))_n layers built up of VO_6 octahedra. Cu ions exhibit non usual tetrahedral coordination and CN = 3 + 2 polyhedra making the estimation of the electric balance between the couples Cu~+-Cu~(2+) and V~(4+) -V~(5+) 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 light of its structural features.