A new charge density wave oxide, $LiVMoO_5$ and its tungsten analogue obtained by topotactic reduction of $LiVMO_6$ (M=Mo,W) brannerites

Abstract

We report the synthesis of two new low-dimensional oxides, LiVMO(5) (M = Mo, W), which contain S = 1/2 transition-metal atoms, V-IV:3d(1) and Mo-V:4d(1)/W-V:5d(1), by topotactic reduction of the LiVMO(6) brannerites in hydrogen. LiVMO(5) crystallizes in orthorhombic structures related to the parent brannerite structure. The VMO(5) network of the new oxides is likely to correspond to one of the A(2)X(5) structures predicted by A. F. Wells (Philos. Trans. R. Soc. London 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