Structural aspects of the metal-insulator transition in BaVS3
  A sequence of structural transitions occurring in the quasi-one-dimensional (1D) 3d1 system BaVS3 at low temperature was investigated by high resolution synchrotron X-ray diffraction. The orthorhombic Cmc21 structure of the intermediate-temperature (70K<T<240K) phase was confirmed. A model for the low-T (T<70K) k=(1 0 1/2)O superstructure (with Im symmetry) is proposed and refined. The formation of the superstructure is associated with the stabilization of a mixed bond order / charge density wave. 
S. Fagot, P. Foury-Leylekian, S. Ravy, J.P. Pouget, M. Anne, G. Popov,   M.V. Lobanov, M. Greenblatt