Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Probing the Ionic Dielectric Constant Contribution in the Ferroelectric
  Phase of the Fabre-Salts   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 the quasi-one
dimensional (TMTTF)$_2X$ Fabre-salts. However, the stabilization of a
long-range ferroelectric ground-state below $T_{co}$ requires the break of
inversion symmetry, which should be accompanied by a lattice deformation. In
this work we investigate the role of the monovalent counter-anion $X$ in such
mechanism. For this purpose, we measured the quasi-static dielectric constant
along the $c^{*}$-axis direction, where layers formed by donors and anions
alternate. Our findings show that the ionic charge contribution is three orders
of magnitude lower than the intra-stack electronic response. The $c^{*}$
dielectric constant ($\epsilon'_{c^*}$) probes directly the charge response of
the monovalent anion $X$, since the anion mobility in the structure should help
to stabilize the ferroelectric ground-state. Furthermore, our $\epsilon'_{c^*}$
measurements %conjugated with earlier investigations of the $c^*$ lattice
thermal expansion, show that the dielectric response is thermally broaden below
$T_{co}$ if the ferroelectric transition occurs in the temperature range where
the anion movement begin to freeze in their methyl groups cavity. In the
extreme case of the PF$_6$-H$_{12}$ salt, where $T_{co}$ occurs at the freezing
point, a relaxor-type ferroelectricity is observed. Also, because of the slow
kinetics of the anion sub-lattice, global hysteresis effects and reduction of
the charge response upon successive cycling are observed. In this context, we
propose that anions control the order-disorder or relaxation character of the
ferroelectric transition of the Fabre-salts.

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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: physics
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The categories of this paper are: comp-gas
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: cs
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The categories of this paper are: astro-ph