Charge ordering in substituted and non-stoichiometric BaVS₃

¹  Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502 - 91405 Orsay Cedex, France, EU
²  Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette cedex, France, EU
³  IMEM-CNR, Area delle Scienze - 43100 Parma, Italy, EU
⁴  Université Pierre et Marie Curie-IMPMC, CNRS-UMR 7590 - 140 rue de Lourmel, 75015 Paris, France, EU
⁵  Institute of Physics of Complex Matter, Ecole Polytechnique Fédérale de Lausanne - CH-1015 Lausanne, Switzerland

Received: 3 November 2009
Accepted: 21 December 2009

Abstract

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 Ba_1-xSr_xVS₃ and in non-stoichiometric BaVS_3-δ, 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.