title: Above Room Temperature Organic Ferroelectrics: Diprotonated 1,4-Diazabicyclo[2.2.2]octane Shifts between Two 2-Chlorobenzoates.
abstract: A pure organic single crystal, [H2dabco]·[2CB]2 ([H2dabco](2+) = diprotonated 1,4-diazabicyclo[2.2.2]octane, 2CB(-) = 2-chlorobenzoate), which undergoes a ferroelectric-to-paraelectric phase transition above room temperature (∼323 K upon heating), was prepared and characterized. This ferroelectric crystal possesses a distinctive supramolecular architecture composed of discrete H-bonded trimeric units (two 2CB(-) anions bridged by one [H2dabco](2+) cation through N-H···O hydrogen bond interactions). In the paraelectric phase, the [H2dabco](2+) cation is rotationally disordered and lies at the symmetric center of the trimer. Upon cooling, it is frozen in an ordered state and deviates toward a 2CB(-) anion at one end along the H-bond. The collective displacement of the cations leads to a polarization of the single crystal along the crystallographic c axis, which is confirmed by the temperature dependence of the second harmonic generation and spontaneous polarization. A significant increase in the phase transition temperature of the deuterated analogue suggests that the proton plays an important role in the ferroelectric phase transition.
authors: Institute for Materials Chemistry and Engineering, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors: Zi-Shuo
authors: ZS
authors: Yao
authors: Department of Applied Physics, Okayama University of Science , Okayama 700-0005, Japan.
authors: Kaoru
authors: K
authors: Yamamoto
authors: National Laboratory of Solid State Microstructures and School of Physics, Nanjing University , Nanjing 210093, P.R. China.
authors: Hong-Ling
authors: HL
authors: Cai
authors: Department of Chemistry, Graduate School of Science, Kobe University , Kobe 657-8501, Hyogo, Japan.
authors: Kazuyuki
authors: K
authors: Takahashi
authors: Institute for Materials Chemistry and Engineering, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors: Osamu
authors: O
authors: Sato