Ferroelectric Order of Parallel Bistable Hydrogen Bonds

Abstract

A new $\mathrm{N}\mathrm{H}\mathrm{\cdots }\mathrm{N}$ hydrogen-bonded ferroelectric crystal of $[{\mathrm{C}}_{\mathrm{6}}{\mathrm{H}}_{\mathrm{12}}{\mathrm{N}}_{\mathrm{2}}\mathrm{H}{\mathrm{]}}^{\mathrm{+}}\mathrm{R}\mathrm{e}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{-}}$ ($\mathrm{d}\mathrm{a}\mathrm{b}\mathrm{c}\mathrm{o}\mathrm{H}\mathrm{R}\mathrm{e}{\mathrm{O}}_{\mathrm{4}}$) exhibits exceptional dielectric properties that result from the unique structure where all the bistable $\mathrm{N}\mathrm{H}\mathrm{\cdots }\mathrm{N}$ hydrogen bonds are parallel and directed exactly in the same sense. Consequently, the main structural origin of the spontaneous polarization of the crystal is the identical orientation of the asymmetric $\mathrm{N}{\mathrm{H}}^{\mathrm{+}}\mathrm{\cdots }\mathrm{N}$ hydrogen bonds along [001]. This first observation of a ferroelectric with parallel arrangement of the $\mathrm{N}{\mathrm{H}}^{\mathrm{+}}\mathrm{\cdots }\mathrm{N}$ bonded aggregates, gives temperature-independent and the highest spontaneous polarization ever reported for an organic or water-soluble substance.