Crystal structure of a new vanadium(IV) diphosphate: VP2O7, prepared by lithium extraction from LiVP2O7

A new vanadium(IV) diphosphate, VP₂O₇, was obtained by lithium extraction from LiVP₂O₇. The parent compound, LiVP₂O₇, is built on [P₂O₇] groups and [VO₆] octahedra and its structure has been confirmed by Synchrotron X-ray powder diffraction. The extraction of one lithium, both electrochemically or chemically, leads to VP₂O₇ which presents a totally different diffraction pattern diagram. The crystal structure of this new compound was determined from Synchrotron X-ray powder diffraction on the chemically prepared sample. The framework of LiVP₂O₇ is maintained upon lithium extraction, and VP₂O₇ crystallizes in space group P2₁. Compared to LiVP₂O₇, there is a very large cell distortion due to a modification of the shape of the tunnels that contained lithium ions along with an oxidation of the vanadium V^III to V^IV that induces shorter V–O bond lengths. The phase transformation from LiVP₂O₇ to VP₂O₇ is found to be displacive and not reconstructive.