Charge ordering and ferroelectric states in organic quasi-one-dimensional conductors

Abstract
In quasi-one-dimensional (TMTTF) ₂X conductors [1], where X are the various centro-symmetrical and non-centrosymmetrical anions, by study of temperature dependences of conductance G and dielectric permittivity at low frequencies we have found anomalies which are characteristic for phase transitions: an abrupt bend on the G(l/T) dependences with thermally activated decrease of G and sharp maxima of the E ' near the charge ordering temperature corresponding to the E ' divergence according to the Curie law. A number of evidences have been obtained in favor that driving force of these phase transitions is the long range correlated electron interaction yielding the charge ordering along the molecular chains (a lattice version of the Wigner crystal). The anion chains, electrically balanced with molecular chains, are of very importance in the formation and the stabilization of these new phase states. It appears that the form of charge symmetry of the anions determines to a great extent the types of the occurring transitions and the developing ground states.