Structural aspects of the metal-insulator transition in BaVS3

S. Fagot¹, P. Foury¹, J.-P. Pouget¹, S. Ravy², E. Elkaïm², G. Popov³, M.V. Lobanov³, M. Greenblatt³, M. Anne⁴

¹Laboratoire de Physique des Solides (CNRS-UMR 8502), Université Paris-Sud, Bât. 510, 91405 Orsay, France
²Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin - BP 48, 91192 GIF-sur-YVETTE, France

³Dpmt of Chemistry and Chemical Biology, Rutgers, State Univ. of New Jersey, Piscataway, NJ08854,USA
⁴Laboratoire de Cristallographie, CNRS, Bât. F, 25 Av. des martyrs, 38042 Grenoble cedex 9, France

This study presents structural transitions of the one dimensional system BaVS₃ at low temperature by means of high resolution synchrotron powder diffraction. At room temperature the structure is hexagonal (P6₃/mmc) with face sharing VS₆ octahedral chains along the c axis separated by Ba atoms leading to a V-V intrachain distance of 2.808(1)Å and an interchain distance 6.714(1)Å. The hexagonal structure at room temperature becomes orthorhombic (Cmc2₁) at 240K with a V straight chains transformed into uniform zigzag but without significant change in the electronic properties. At 70K a metal-insulator transition occurs with the appearance of a superstructure which doubles the chain periodicity. The structure refined at 40K revealed a weak monoclinic distorsion (b= 90.046(1)°) with 4 nonequivalent V sites. A valence bond analysis shows no evidence for charge disproportionation on these sites. However at 5K, the faces of the VS₆ octahedra are stretched (site V1) or compressed (V3) inducing a 0.5e- charge disproportionation between the V1 and V3 sites.