title: Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability.
abstract: On the basis of an excellent transistor material, [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)2XF6 (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm(-1) in the AsF6 salt, corresponding to the drift mobility of 16 cm(2) V(-1) s(-1). Owing to the high conductivity, this salt shows a thermoelectric power factor of 55-88 μW K(-2) m(-1), which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4kF charge-density waves as an origin of the low-temperature insulating state.
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology , O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kiyota
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology , O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Tomofumi
authors.initials: T
authors.lastname: Kadoya
authors.affiliation: Department of Applied Physics, Okayama University of Science , Ridaicho 1-1, Okayama 700-0005, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology , O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Kodai
authors.initials: K
authors.lastname: Iijima
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology , O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Higashino
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology , O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kawamoto
authors.affiliation: Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science (CEMS) , Wako, Saitama 351-0198, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Takimiya
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology , O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.|ACT-C, JST, Honcho , Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Mori