ON THE INCOMMENSURATELY MODULATED STRUCTURE OF EPSILON'-LIXV2O5 AT ROOM-TEMPERATURE

Electron diffraction was used to study the lithium-intercalated V2O5 b ronzes LixV2O5. In the course of these investigations a new incommensu rately modulated structure was detected at room temperature. The space group of the basic structure is Pmmn; the superspace group characteri zing the one-dimensionally modulated structure is found to be Pmmn (0 gamma 1/2). The incommensurate component gamma of the modulation vecto r q is a function of the lithium stoichiometry and varies between gamm a = 0.531(4) and gamma = 0.550(4) for epsilon'-LixV2O5 with 0.605(3) l ess than or equal to x less than or equal to 0.620(3). In the present paper we propose that an important contribution to the modulation resu lts from repulsive Li+-Li+ forces, which impose an incommensurate orde ring of the Li+ ions along b in strings of cuboctahedral cavities bet ween adjacent V2O5 layers.