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arXiv · 0807.0735

Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)$_2$X

M. de Souza·P. Foury-Leylekian·A. Moradpour·J. -P. Pouget·M. Lang
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Abstract

High-resolution thermal expansion measurements have been performed for exploring the mysterious "structureless transition" in (TMTTF)$_{2}$X (X = PF$_{6}$ and AsF$_{6}$), where charge ordering at $T_{CO}$ coincides with the onset of ferroelectric order. Particularly distinct lattice effects are found at $T_{CO}$ in the uniaxial expansivity along the interstack $\textbf{\textit{c*}}$-direction. We propose a scheme involving a charge modulation along the TMTTF stacks and its coupling to displacements of the counteranions X$^{-}$. These anion shifts, which lift the inversion symmetry enabling ferroelectric order to develop, determine the 3D charge pattern without ambiguity. Evidence is found for another anomaly for both materials at $T_{int}$ $\simeq$ 0.6 $\cdot$ $T_{CO}$ indicative of a phase transition related to the charge ordering.

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M. de Souza, P. Foury-Leylekian, A. Moradpour, J. -P. Pouget, M. Lang. 2008-11-24. Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)$_2$X. https://doi.org/10.1103/physrevlett.101.216403

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