On the incommensurately modulated structure of ε′-Li_xV₂O₅ at room temperature

Abstract

Electron diffraction was used to study the lithium-intercalated V₂O₅ bronzes Li _x V₂O₅. In the course of these investigations a new incommensurately modulated structure was detected at room temperature. The space group of the basic structure is Pmmn; the superspace group characterizing the one-dimensionally modulated structure is found to be Pmmn (0 γ ½). The incommensurate component γ of the modulation vector q is a function of the lithium stoichiometry and varies between γ = 0.531(4) and γ = 0.550(4) for ε′-Li _x V₂O₅ with 0.605(3) ≤ x ≤ 0.620(3).

In the present paper we propose that an important contribution to the modulation results from repulsive Li⁺-Li⁺ forces, which impose an incommensurate ordering of the Li⁺ ions along b* in strings of cuboctahedral cavities between adjacent V₂O₅ layers.