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Double Layer Conducting Salts: (CNB-EDT-TTF)4X, X = ClO4, ReO4, and SbF6; Electrical Transport and Infrared Properties

1
C2TN, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, P-2695-066 Bobadela LRS, Portugal
2
Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
*
Authors to whom correspondence should be addressed.
Crystals 2019, 9(12), 608; https://doi.org/10.3390/cryst9120608
Received: 9 October 2019 / Revised: 15 November 2019 / Accepted: 17 November 2019 / Published: 20 November 2019
(This article belongs to the Section Inorganic Crystalline Materials)
Two new members of the family of bilayer compounds (CNB-EDT-TTF)4X, (CNB-EDT-TTF = 5-cyanobenzene-ethylenedithio-tetrathiafulvalene) with anions X = ReO4 and SbF6 are reported, their electron transport and optical properties investigated, and then compared to the ClO4 salt that was previously described. These compounds share the same structural type, i.e. bilayers of donors, which are packed in a β″-type pattern and then separated by layers of highly disordered anions. The absolute values of the electrical resistivity measured in single crystals within the layers were found in the range of 5 to 18 (Ωcm)−1, with a significantly sample dependence being ascribed to intrinsic disorder effects. The ClO4 and SbF6 salts exhibit metallic behavior with the resistivity decreasing upon cooling almost linearly with temperature until a broad minimum is reached between 15 and 80 K, depending on crystal quality; this is followed by an upturn of resistivity reaching values at T = 1.5 K that were comparable to those attained at room temperature. The electrical resistivity of the ReO4 salt follows a thermally activated behavior already at T = 300 K, although with a small activation energy in the range 16−18 meV. Thermoelectric power measurements yield large positive values (75–80 µV/K) at ambient temperature with a metallic behavior that is identical for all compounds. Temperature and polarization dependent infrared reflection measurements on single crystals of (CNB-EDT-TTF)4X salts, with X = ClO4, ReO4, and SbF6, have been performed to obtain the optical conductivity and analyze the electronic and vibrational properties. For (CNB-EDT-TTF)4ClO4 the molecular vibrations exhibit a significant variation below T = 23 K, which suggests a charge localization phenomena. View Full-Text
Keywords: two-dimensional molecular metals; bilayer structure; electrical resistivity; thermoelectric power; optical conductivity; IR spectra two-dimensional molecular metals; bilayer structure; electrical resistivity; thermoelectric power; optical conductivity; IR spectra
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MDPI and ACS Style

Oliveira, S.; Gonçalves, A.C.; Oliveira, G.; Günther, D.; Rohwer, A.; Gama, V.; Lopes, E.B.; Santos, I.C.; Rabaça, S.; Almeida, M.; Dressel, M. Double Layer Conducting Salts: (CNB-EDT-TTF)4X, X = ClO4, ReO4, and SbF6; Electrical Transport and Infrared Properties. Crystals 2019, 9, 608. https://doi.org/10.3390/cryst9120608

AMA Style

Oliveira S, Gonçalves AC, Oliveira G, Günther D, Rohwer A, Gama V, Lopes EB, Santos IC, Rabaça S, Almeida M, Dressel M. Double Layer Conducting Salts: (CNB-EDT-TTF)4X, X = ClO4, ReO4, and SbF6; Electrical Transport and Infrared Properties. Crystals. 2019; 9(12):608. https://doi.org/10.3390/cryst9120608

Chicago/Turabian Style

Oliveira, Sandrina; Gonçalves, Ana C.; Oliveira, Gonçalo; Günther, Dominik; Rohwer, Andrea; Gama, Vasco; Lopes, Elsa B.; Santos, Isabel C.; Rabaça, Sandra; Almeida, Manuel; Dressel, Martin. 2019. "Double Layer Conducting Salts: (CNB-EDT-TTF)4X, X = ClO4, ReO4, and SbF6; Electrical Transport and Infrared Properties" Crystals 9, no. 12: 608. https://doi.org/10.3390/cryst9120608

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