Electron–Intramolecular Vibration Coupling in Charge-Transfer Salts Studied by Infrared Spectroscopy

Yartsev, V. M.; Graja, A.

doi:10.1142/s0217979298000909

Cited by 32 publications

(32 citation statements)

References 87 publications

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“…The coupling constants of ν 2 and ν 3 were respectively estimated to be g 2 = 0.043 and g 3 = 0.071 eV from an analysis of the infrared spectrum of the isolated dimer (BEDT-TTF) 2 2+ [53]. The parameters estimated from the infrared spectra were very scattered (g 2 ~ 0.007-0.039 eV and g 3 = 0.007-0.081 eV) depending upon the compounds [54]. A more recent estimation gives g 3 = 0.076 eV from the analysis of the infrared spectrum of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]-Br 0.85 Cl 0.15 [55].…”

Section: Electron-molecular Vibration (Emv) Coupling In Bedt-ttfmentioning

confidence: 99%

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Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Yakushi

2012

Crystals

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This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF) 2 X, and α-(BEDT-TTF) 2 X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy in addition to optical conductivity measurements. It was found that β″-(BEDT-TTF)(TCNQ) changes continuously from a uniform metal to a chargeordered metal with increasing temperature. Although charge disproportionation was clearly observed, long-range charge order is not realized. Among six θ-type salts, four compounds with a narrow band show the metal-insulator transition. However, they maintain a large amplitude of charge order (Δρ~0.6) in both metallic and insulating phases. In the X = CsZn(SCN) 4 salt with intermediate bandwidth, the amplitude of charge order is very small (Δρ < 0.07) over the whole temperature range. However, fluctuation of charge order is indicated in the Raman spectrum and optical conductivity. No indication of the fluctuation of charge order is found in the wide band X = I 3 salt. In α-(BEDT-TTF) 2 I 3 the amplitude of charge order changes discontinuously from small amplitude at high temperature to large amplitude (Δρ max~0 .6) at low temperature. The long-range chargeordered state shows ferroelectric polarization with fast optical response. The fluctuation of multiple stripes occurs in the high-temperature metallic phase. Among α-(BEDT-TTF) 2 MHg(SCN) 4 (X = NH 4 , K, Rb, Tl), the fluctuation of charge order is indicated only in the X = NH 4 salt. α′-(BEDT-TTF) 2 IBr 2 shows successive phase transitions to the ferroelectric state keeping a large amplitude of charge order (Δρ max~0 .8) over the whole temperature range. It was found that the amplitude and fluctuation of charge order in these compounds is enhanced as the kinetic energy (bandwidth) decreases. OPEN ACCESSCrystals 2012, 2 1292

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Section: Electron-molecular Vibration (Emv) Coupling In Bedt-ttfmentioning

confidence: 99%

“…The downshift of this mode is sensitive to the transfer integrals between BEDT-TTF molecules (see ref. [54] for example). Yamamoto et al, discussed the relation between the downshift of ν 3B and transfer integrals comparing the ν 3 modes among several θ-type of BEDT-TTF salts.…”

Section: Electron-molecular Vibration (Emv) Coupling In Bedt-ttfmentioning

confidence: 99%

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Yakushi

2012

Crystals

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“…[39][40][41][42][43] Thus, vibronic features are well known to provide a microscopic probe of the interactions in organic solids, with mode intensities relating directly to the square of the order parameter of the lattice distortion. In ␤Љ-(ET) 2 SF 5 CH 2 CF 2 SO 3 , the high-temperature couplingallowed features are weak in Ќb polarization; even the three strongest vibronic modes ͑1350, 890, and 439 cm Ϫ1 ) are barely visible.…”

Section: B Vibrational Featuresmentioning

confidence: 99%

“…It is well established that most of the observed phonon features are due to the totally symmetric A g modes of intramolecular vibrations which couple strongly to the electronic excitations. [39][40][41][42][43] Therefore, vibronic features provide a window into both vibrational and electronic interactions in ETbased organic conductors. Previous infrared and Raman studies on various phases of ET conductors, [44][45][46][47] phase in particular, 30,48,49 have provided comprehensive assignments of intramolecular phonon modes.…”

Section: Introductionmentioning

confidence: 99%

Optical properties ofβ″−(ET)2SF5

et al. 1999

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We report the polarized infrared and optical reflectance of ␤Љ-(ET) 2 SF 5 CH 2 CF 2 SO 3 as a function of temperature. This fully organic superconductor displays weakly metallic behavior over the entire temperature range of our investigation. The electronic properties present several unusual features including the lack of a conventional free carrier ͑Drude͒ response at low temperature, infrared localization phenomena, and an unexpected temperature dependence of the oscillator strength. Similar behavior is observed in other ␤ and ␤Љ superconductors above T c , suggesting that this class of compounds is very close to a metal˜insulator transition where electronic correlations are important and the Drude response carries very little spectral weight. Vibronic features increase in intensity with decreasing temperature in the infrared, as expected. The temperature dependence of key anion vibrational modes are discussed in terms of intermolecular hydrogen bonding within the anion pocket. ͓S0163-1829͑99͒04330-1͔

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“…As mentioned above, models of EMV coupling are universal and were successfully applied to IR spectra of charge-transfer salts formed by TTF (TTF = tetrathiafulvalene) and its derivatives with various acceptors [14]. More specifically, the dimer model has proven especially useful in determining the coupling constants for charge transfer materials containing TTF derivatives.…”

Section: Introductionmentioning

confidence: 99%

Electron-molecular vibration coupling in (DMtTTF)Br and (o-DMTTF)2[W6O19] salts studied by vibrational spectroscopy

et al. 2014

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Electron–Intramolecular Vibration Coupling in Charge-Transfer Salts Studied by Infrared Spectroscopy

Cited by 32 publications

References 87 publications

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Optical properties ofβ″−(ET)2SF5

Electron-molecular vibration coupling in (DMtTTF)Br and (o-DMTTF)2[W6O19] salts studied by vibrational spectroscopy

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