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Crystals 2012, 2(3), 893-934; doi:10.3390/cryst2030893
Review

Vibrational Spectra of β″-Type BEDT-TTF Salts: Relationship between Conducting Property, Time-Averaged Site Charge and Inter-Molecular Distance

Received: 18 April 2012; in revised form: 20 June 2012 / Accepted: 26 June 2012 / Published: 6 July 2012
(This article belongs to the Special Issue Molecular Conductors)
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Abstract: The relationship between the conducting behavior and the degree of charge fluctuation in the β″-type BEDT-TTF salts is reviewed from the standpoints of vibrational spectroscopy and crystal structure. A group of β″-type ET salts demonstrates the best model compounds for achieving the above relationship because the two-dimensional structure is simple and great diversity in conducting behavior is realized under ambient pressure. After describing the requirement for the model compound, the methodology for analyzing the results of the vibrational spectra is presented. Vibrational spectroscopy provides the time-averaged molecular charge, the charge distribution in the two-dimensional layer, and the inter-molecular interactions, etc. The experimental results applied to 2/3-filled and 3/4-filled β″-type ET salts are reported. These experimental results suggest that the conducting property, the difference in the time-averaged molecular charges between the ionic and neutral-like sites, the alternation in the inter-molecular distances and the energy levels in the charge distributions are relevant to one another. The difference in the time-averaged molecular charges, ∆ρ, is a useful criterion for indicating conducting behavior. All superconductors presented in this review are characterized as small but finite ∆ρ.
Keywords: two-dimensional molecular conductor; superconductivity; charge fluctuation; charge ordered state; vibrational spectroscopy; inter-molecular distance; bis(ethylenedithio)tetrathiafulvalene; β″-type structure; phase diagram two-dimensional molecular conductor; superconductivity; charge fluctuation; charge ordered state; vibrational spectroscopy; inter-molecular distance; bis(ethylenedithio)tetrathiafulvalene; β″-type structure; phase diagram
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MDPI and ACS Style

Yamamoto, T. Vibrational Spectra of β″-Type BEDT-TTF Salts: Relationship between Conducting Property, Time-Averaged Site Charge and Inter-Molecular Distance. Crystals 2012, 2, 893-934.

AMA Style

Yamamoto T. Vibrational Spectra of β″-Type BEDT-TTF Salts: Relationship between Conducting Property, Time-Averaged Site Charge and Inter-Molecular Distance. Crystals. 2012; 2(3):893-934.

Chicago/Turabian Style

Yamamoto, Takashi. 2012. "Vibrational Spectra of β″-Type BEDT-TTF Salts: Relationship between Conducting Property, Time-Averaged Site Charge and Inter-Molecular Distance." Crystals 2, no. 3: 893-934.

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