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Abstract: The one-dimensional (1D) 3d1 system BaVS3 undergoes a metal–insulator (MI) transition at , 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 5K, we present structural evidence for a charge disproportionation on the V sites, accompanied by a distortion wave of the sulphur octahedra. [Copyright &y& Elsevier]

Abstract: BaVS3 is an unusual 3d1 quasi-one dimensional (1D) correlated system presenting an interplay of charge, orbital and spin degrees of freedom. At , BaVS3 undergoes a metal–insulator transition whose origin is still a matter of controversy. We show that this transition is associated with a structural modulation preceded by an extended temperature range of 1D lattice fluctuations. We have refined the superstructure and showed that it corresponds to a complex modulation of the V bonds leading to the formation of an Unconventional Charge Density Wave (CDW) ground state. [Copyright &y& Elsevier]