title: Unusual High-Temperature Reversible Phase-Transition Behavior, Structures, and Dielectric-Ferroelectric Properties of Two New Crown Ether Clathrates.
abstract: Molecular ferroelectrics with high-temperature reversible phase-transition behaviors are very rare and have currently become one of the hotspots in the field of ferroelectric materials. Herein we display two new crown ether clathrates possessing unusual high-temperature ferroelectric phase-transition behaviors, cyclohexyl ammonium 18-crown-6 tetrafluoroborate (or perchlorate), [Hcha-(18-crown-6)](+) [BF4](-) (1) and [Hcha-(18-crown-6)](+)[ClO4](-) (2) (Hcha = protonated cyclohexyl ammonium). We have proven their reversible structural phase transitions by variable-temperature PXRD measurements and temperature evolutions of Raman bands. Both clathrates exhibit clear ferroelectric phase transitions at about 397 and 390 K, respectively, revealed by the thermal anomalies of differential scanning calorimetry (DSC) measurements, together with abrupt dielectric anomalies in the heating and cooling processes. The measurements on ferroelectric properties using the single crystals showed optimized spontaneous polarization (Ps) of ca. 3.27 μC cm(-2) for 1 and 3.78 μC cm(-2) for 2.
authors.affiliation: School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology , Ganzhou 341000, PR China.
authors.forename: Yun-Zhi
authors.initials: YZ
authors.lastname: Tang
authors.affiliation: School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology , Ganzhou 341000, PR China.
authors.forename: Yin-Mei
authors.initials: YM
authors.lastname: Yu
authors.affiliation: School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology , Ganzhou 341000, PR China.
authors.forename: Jian-Bo
authors.initials: JB
authors.lastname: Xiong
authors.affiliation: School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology , Ganzhou 341000, PR China.
authors.forename: Yu-Hui
authors.initials: YH
authors.lastname: Tan
authors.affiliation: School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology , Ganzhou 341000, PR China.
authors.forename: He-Rui
authors.initials: HR
authors.lastname: Wen