Structural aspects of the metal-insulator transition in BaVS3

The one-dimensional (1D) 3d(1) system BaVS3 undergoes a metal-insulator (MI) transition at T-MI = 70 K, whose origin is still a matter of controversy. We show that the MI transition is accompanied by the formation of a superstructure which doubles the chain periodicity. The superstructure has been refined in the monoclinic Im space group from high resolution X-ray synchrotron powder diffraction. We show that the MI transition sets a bond order wave on the V chains. At 5 K, we present structural evidence for a charge disproportionation on the V sites, accompanied by a distortion wave of the sulphur octahedra. (c) 2005 Elsevier B.V. All rights reserved.