Lithium and sodium insertion reactions of phosphate tungsten bronzes

Abstract

Lithium insertion reactions of monophosphate tungsten bronzes, (PO 2) 4(WO 3) 2 m and diphosphate tungsten bronzes K(P 2O 4) 2(WO 3) 2 m indicate that a maximum of two Li/W and one Na/W may be inserted in these materials. The phosphate tungsten bronzes are three-dimensional network structures made up of slabs of ReO 3-type WO 6 octahedra connected by phosphate groups with large interconnected cavities. Ion-exchange reactions of selected members of K(P 2O 4) 2(WO 3) 2 m show that potassium which occupies the large hexagonal tunnels in the lattice may be exchanged for various alkali metal cations. Upon lithium insertion, the metallic host materials become insulating. This is attributed to the filling of the π* conduction band formed by the overlap of Wt 2g − 5d and oxygenπ − 2p orbitals.