Probing the ionic dielectric constant contribution in the ferroelectric phase of the Fabre salts

摘要: In strongly correlated organic materials it has been pointed out that charge ordering could also achieve electronic ferroelectricity at the same critical temperature ${T}_{co}$. A prototype of such phenomenon are quasi-one-dimensional $({\mathrm{TMTTF})}_{2}X$ Fabre salts. However, stabilization a long-range ferroelectric ground state below ${T}_{co}$ requires break inversion symmetry, which should be accompanied by lattice deformation. this paper we investigate role monovalent counteranion $X$ in mechanism. For purpose, measured quasistatic dielectric constant along ${c}^{*}$-axis direction, where layers formed donors and anions alternate. Our findings show ionic contribution is three orders magnitude lower than intrastack response. The ${c}^{*}$ $({\ensuremath{\epsilon}}_{{c}^{*}}^{\ensuremath{'}})$ probes directly response anion $X$, since mobility structure help to stabilize state. Furthermore, our ${\ensuremath{\epsilon}}_{{c}^{*}}^{\ensuremath{'}}$ measurements thermally broaden if transition occurs range movement begin freeze their methyl groups cavity. extreme case ${\mathrm{PF}}_{6}\text{\ensuremath{-}}{\mathrm{H}}_{12}$ salt, freezing point, relaxor-type observed. Also, because slow kinetics sublattice, global hysteresis effects reduction upon successive cycling context, propose control order-disorder or relaxation character Yet, results x-ray irradiation damages change well-defined ${\mathrm{AsF}}_{6}$ pristine salt into relaxor.