Structural and electrical properties of (TMTTF)2MF6 salts (M = P, As, Sb). Rôle of the anions

Laversanne, R.; Coulon, C.; Gallois, B.; Pouget, J.P.; Moret, R.

doi:10.1051/jphyslet:01984004508039300

Cited by 115 publications

(110 citation statements)

References 12 publications

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“…We present results on a sample with a regular cross-section of 4 10 −5 cm 2 and a length of 3 mm. Its room temperature conductivity was about 10 Ω −1 cm −1 close to the value previously published [5]. The complex conductance G(T ) was measured in the frequency range 1kHz − 10MHz using an impedance analyzer HP 4192A.…”

supporting

confidence: 80%

“…Very soon NMR studies have proved [4] that the transitions at T 0 are related to charge disproportionation, also called charge ordering (CO), dividing molecules within in two non equivalent species. Previous reports on T MT T F salts with larger anions such as SbF 6 have suggested the occurrence of a phase transition, sometimes called " structureless" transition, at a temperature of the scale of T a showing itself in changes of the resistance [5] and the thermopower [6], in weak features in high frequency (∼ GHz) dielectric susceptibility [7].…”

mentioning

confidence: 96%

“…However, X− rays investigations brought no observation of superlattice reflections [5] while some variation of intensity of Bragg reflections could actually have been noticed [16]. NMR allows to identify the very fact of the CO via nonequivalence of molecular sites [4,8] but it cannot distinguish between the q = 0 state and the known undulating ones (either along the stack like the 4k F (Wigner) condensation in (DCNQI) 2 Ag [8] or between stacks like in (T MT T F ) 2 SCN) [2]).…”

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confidence: 99%

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Ferroelectric Mott-Hubbard Phase of Organic(TMTTF)2XConductors

2001

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We present experimental evidences for a ferro-electric transition in the family of quasi-one-dimensional conductors (T M T T F ) 2 X. We interpret this new transition in the frame of the combined Mott-Hubbard state taking into account the double action of the spontaneous charge disproportionation on the T M T T F molecular stacks and of the X anionic potentials.PACS numbers: 71.30 +h, 7127 +a, 77.80.Bh, 7145.Lr Low dimensional electronic systems serve as a workshop on problems of strong correlations. The richest opportunities have been opened by the family of charge transfer salts M 2 X formed of stacks of organic molecules tetramethyltetrathiofulvalene (M = T MT T F ) or tetramethyltetraselenafulvalene (M = T MT SF ) with anions X = P F 6 , AsF 6 , SbF 6 , SCN, etc as counterions. The ions sit in loose cavities delimited by the methyl groups of the organic molecules. These materials show almost all known electronic phases: a metal, a paramagnetic insulator (PI), spin/charge density waves (SDW/CDW), the spin-Peierls state and finally the superconducting state [1]. In parallel, there is a set of several different structural types due to anion ordering (AO) which are slight arrangements in X chains [2]. Their tran-1 sition temperatures T a ≈ 100 − 200K are much higher than that corresponding to electronic transitions occurring in the range of T c ≈ 1 − 10K.Very recently, in the already very rich phase diagram of these salts, a new phase transition has been discovered, being revealed by a huge anomaly in the low frequency dielectric constant ǫ ′ at T 0 = 70K in (T MT T F ) 2 P F 6 and at 100K in (T MT T F ) 2 AsF 6 [3]. Very soon NMR studies have proved [4] that the transitions at T 0 are related to charge disproportionation, also called charge ordering (CO), dividing molecules within in two non equivalent species. Previous reports on T MT T F salts with larger anions such as SbF 6 have suggested the occurrence of a phase transition, sometimes called " structureless" transition, . So, the identification of the nature of this " structureless" q = 0 transition was still unsolved. We show hereafter that ǫ ′ in (T MT T F ) 2 SbF 6 , as in the case of (T MT T F ) 2 P F 6 and (T MT T F ) 2 AsF 6 , exhibits a huge divergence at 154K. Dielectric experiments are providing thus an unique access to the anomalous collective properties of this mysterious transition identifying the resulting state as a never expected ferroelectric (FE) one.In the high temperature range T > T a , T 0 the counterions already have a profound effect on the electronic properties: the anions dimerize the intermolecular spacing of the TMTTF molecules along the stacks. As a result, the conduction band is split into a filled lower band separa ted from a half-filled upper band by a dimerization gap, leading to Mott-Hubbard charge localization. The effects brought by the AOs with q = 0 have been previously discussed ( [2,9] and refs. therein). The new effects of combined CO-AO with q = 0 are 2 the main topic of the present work. Empirically one ...

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confidence: 80%

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confidence: 96%

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confidence: 99%

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Ferroelectric Mott-Hubbard Phase of Organic(TMTTF)2XConductors

2001

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“…Only the diffuse lines observed inside the Bragg layers perpendicular to c * seem to disappear around T u . The first feature recalls the behavior 22,75 found in the (TMTTF) 2 X series, where the anomaly in transport measurement was initially believed not to affect the lattice symmetry and was interpreted as a crossover on the charge transport. Actually, recent nuclear magnetic resonance (NMR) detection of a charge disproportionation 18 and the divergence of the dielectric constant 19 were able to show that this anomaly leads to a breaking of the inversion symmetry and that (TMTTF) 2 X undergoes a second-order phase transition to a CO ferroelectric ground state.…”

Section: B the Upper Transition At T Umentioning

confidence: 65%

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(
Foury-Leylekian
¹
,
Auban-Sensier
²
,
Coulon
³

et al. 2011
Phys. Rev. B
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The 2:1 family of organic salts (o-DMTTF) 2 X (X = Cl, Br, I) exhibits regular stacks and a high-symmetry structure, which provide a perfect three-quarter-filling-band system allowing a rich phase diagram in the presence of strong electronic correlations. In this paper, we present a detailed study of this series combining complementary experimental techniques such as resistivity, thermopower, electron spin resonance, static magnetic measurements, and x-ray diffraction. In particular, we show that at ambient pressure (o-DMTTF) 2 X with X = Br and Cl undergoes two successive phase transitions setting successively a 4k F charge density and bond order wave order, then a spin-Peierls (SP) ground state. We discuss the symmetry of these phases and its relationship with the transport and magnetic properties. These phases are also followed under pressure by transport experiments, allowing the establishment of a generic phase diagram for this series of salts, where, with the onset of a one-dimensional to three-dimensional deconfinement transition, the 4k F order vanishes and the SP ground state transforms into a Peierls one. Interestingly, this phase diagram differs significantly from the one previously reported in other three-quarter-filled systems such as (TMTTF) 2 X and δ-(EDT-TTF-CONMe 2 ) 2 X.

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“…It has been known for a long time that properties of certain TMTTF salts, for example (TMTTF) 2 SbF 6 , did not fit into the generally accepted model [20]. The temperature dependence of the resistivity ρ(T) for this material is metallic, that is, dρ/dT>0 down to T=155K, where it appears that a continuous metal-insulator transition takes place [21]. It was referred to as "structureless" because no signature was found in X-ray scattering studies.…”

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confidence: 89%

Charge Ordering in the TMTTF Family of Molecular Conductors

et al. 2000

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Using one-and two-dimensional NMR spectroscopy applied to 13 C spin-labeled (TMTTF)2AsF6 and (TMTTF)2PF6, we demonstrate the existence of an intermediate charge-ordered phase in the TMTTF family of charge-transfer salts. At ambient temperature, the spectra are characteristic of nuclei in equivalent environments, or molecules. Below a continuous charge-ordering transition temperature Tco, the spectra are explained by assuming there are two inequivalent molecules with unequal electron densities. The absence of an associated magnetic anomaly indicates only the charge degrees of freedom are involved and the lack of evidence for a structural anomaly suggests that charge/lattice coupling is too weak to drive the transition.

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Structural and electrical properties of (TMTTF)2MF6 salts (M = P, As, Sb). Rôle of the anions

Cited by 115 publications

References 12 publications

Ferroelectric Mott-Hubbard Phase of Organic(TMTTF)2XConductors

Ferroelectric Mott-Hubbard Phase of Organic(TMTTF)2XConductors

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(
Foury-Leylekian
¹
,
Auban-Sensier
²
,
Coulon
³

et al. 2011
Phys. Rev. B
Self Cite

Charge Ordering in the TMTTF Family of Molecular Conductors

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Structural and electrical properties of (TMTTF)2MF6 salts (M = P, As, Sb). Rôle of the anions

Cited by 115 publications

References 12 publications

Ferroelectric Mott-Hubbard Phase of Organic(TMTTF)2XConductors

Ferroelectric Mott-Hubbard Phase of Organic(TMTTF)2XConductors

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(Foury-Leylekian1, Auban-Sensier2, Coulon3 et al. 2011Phys. Rev. BSelf Cite

Charge Ordering in the TMTTF Family of Molecular Conductors

Contact Info

Product

Resources

About

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(
Foury-Leylekian
¹
,
Auban-Sensier
²
,
Coulon
³

et al. 2011
Phys. Rev. B
Self Cite