Topotactic insertion of lithium in the layered structure Li 4VO(PO 4) 2: The tunnel structure Li 5VO(PO 4) 2

Abstract

A new V(III) lithium phosphate Li 5VO(PO 4) 2 has been synthesized by electrochemical insertion of lithium into Li 4VO(PO 4) 2. This phase, which crystallizes in the space group I4/ mcm, exhibits a tunnel structure closely related to the layered structure of Li 4VO(PO 4) 2 and to the tunnel structure of VO(H 2PO 4) 2. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H 2PO 4) 2 and going to the final phase Li 5VO(PO 4) 2 are explained on the basis of the flexible coordinations of V 4+ and V 3+ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality.