Charge ordering in substituted and non-stoichiometric BaVS3

Among the correlated electronic systems, BaVS3 which exhibits both itinerant and localized states as well as a subtle interplay betwen charge, orbital, spin and lattice degrees of freedom, is a model system. Its electronic structure consists in a broad quasi-one-dimensional (1D) d(z2) band and two quasi-degenerate narrow e(t(2g)) bands. Pure BaVS3 exhibits a metal-insulator transition (MIT) driven by a Peierls instability in the d(z2) band. We present a structural investigation showing that in chemically substituted Ba1-xSrxVS3 and in non-stoichiometric BaVS3-delta, the commensurate Peierls distortion of BaVS3 is replaced by an incommensurate modulation that we attribute to a charge ordering (CO) of the localized e(t(2g)) electrons. This unexpected structural feature is discussed in relationship with the concomitant drastic change of magnetic properties of the system.