An electron diffraction study of Cu ordering in Cu(2.33-x)V₄O₁₁

A temperature-dependent electron diffraction study has been made of Cu ion ordering in the vanadium oxide bronze Cu(2.33-x)V₄O₁₁. Evidence is thereby found (at low temperature) for two distinct incommensurate modulations associated with the three-dimensional ordering of Cu ions in each of two distinct channel types which run along b between the V₄O₁₁ layers of the average structure. The primary modulation wave-vector associated with the first modulation q₁ = 1/2c*+ ~0.12b* is associated with Cu ion ordering and associated structural relaxation in the first type of tunnel while the second type of modulation (characterized by the primary modulation wave-vector q₂= ± 1/2a*+~0.16b*) is presumed to be associated with Cu ion ordering in the remaining, or tetrahedral, tunnel type. This second modulation only appears to condense out at low temperature.