title: Above-room-temperature ferroelectricity and antiferroelectricity in benzimidazoles.
abstract: The imidazole unit is chemically stable and ubiquitous in biological systems; its proton donor and acceptor moieties easily bind molecules into a dipolar chain. Here we demonstrate that chains of these amphoteric molecules can often be bistable in electric polarity and electrically switchable, even in the crystalline state, through proton tautomerization. Polarization-electric field (P-E) hysteresis experiments reveal a high electric polarization ranging from 5 to 10 μC cm(-2) at room temperature. Of these molecules, 2-methylbenzimidazole allows ferroelectric switching in two dimensions due to its pseudo-tetragonal crystal symmetry. The ferroelectricity is also thermally robust up to 400 K, as is that of 5,6-dichloro-2-methylbenzimidazole (up to ~373 K). In contrast, three other benzimidazoles exhibit double P-E hysteresis curves characteristic of antiferroelectricity. The diversity of imidazole substituents is likely to stimulate a systematic exploration of various structure-property relationships and domain engineering in the quest for lead- and rare-metal-free ferroelectric devices.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8562, Japan. s-horiuchi@aist.go.jp
authors.forename: Sachio
authors.initials: S
authors.lastname: Horiuchi
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Kagawa
authors.forename: Kensuke
authors.initials: K
authors.lastname: Hatahara
authors.forename: Kensuke
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Reiji
authors.initials: R
authors.lastname: Kumai
authors.forename: Youichi
authors.initials: Y
authors.lastname: Murakami
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Tokura