A new charge density wave oxide, LiVMoO₅, and its tungsten analogue obtained by topotactic reduction of LiVMO₆ (M= Mo,W) brannerites

Abstract

We report the synthesis of two new low-dimensional oxides, LiVMO₅ (M=Mo, W), which contain S=½ transition-metal atoms, V^IV:3d¹ and Mo^V:4d¹/W^V:5d¹, by topotactic reduction of the LiVMO₆ brannerites in hydrogen. LiVMO₅ crystallizes in orthorhombic structures related to the parent brannerite structure. The VMO₅ network of the new oxides is likely to correspond to one of the A₂X₅ structures predicted by A. F. Wells (Philos. T rans. R. Soc. L ondon A, 1984, 312, 589). LiVMoO₅ is metallic showing a charge density wave (CDW) instability around 230 K; interestingly, LiVWO₅ is a paramagnetic semiconductor down to 20 K.