MgV2O5andδLixV2O5: A Comparative Structural Investigation

The structures of MgV2O5andδLiV2O5have been determined form X-ray powder diffraction Rietveld analysis at 294 and 83 K. The compounds crystallize in the orthorhombic system, space groupCmcm, with the following cell parameters (Å): at 294 K,aMg=3.6913(2),bMg=9.9710(4),cMg=11.0173(4),aLi= 3.6047(2),bLi=9.9157(5),cLi=11.2479(4); at 83 K,aMg= 3.6928(2),bMg=9.9576(3),cMg=11.0096(4),aLi=3.6031(2),bLi=9.8734(4),cLi=11.2350(4). The general network, with four formulas per unit, is built up by parallel puckered [V2O5]nlayers of [VO5] square pyramids sharing edges and corners alternately shifted bya/2 in the [100] direction and held together by intercalated Mg or Li atoms. The main difference between the two is induced by the higher polarization of the magnesium atoms compared to the lithium atoms, which leads to higher puckering angles of 21.0° and 11.3°, respectively. Both magnesium and lithium atoms are surrounded by four close oxygens making a distorted tetrahedron. Despite the presence of both V4+and V5+inδLiV2O5, no electronic localization occurs at the crystallographic sites corresponding to these vanadium species. This fact could be attributed to the low energy available to the system during the low-temperature synthesis.