Rational Design of Ceramic-Like Molecular Ferroelectric by Quasi-Spherical Theory

Molecular ferroelectrics are attracting tremendous interest because of their easy and environmentally friendly processing, light weight, low acoustical impedance and mechanical flexibility, which are viable alternatives or supplements to conventional ceramic ferroelectrics. However, reports of ceramic-like molecular ferroelectrics that can be applied in the polycrystalline form have been scarce. Here, according to the “quasi-spherical theory”, we successfully synthesized a ceramic-like molecular ferroelectric with an m3 mFmm2 type phase transition at 357 K, 1, 5-diazabicyclo[3.2.1]octonium tetrafluoroborate ([3.2.1-dabco]BF4), which can show excellent ferroelectric performance in the polycrystalline thin-film form at room temperature. Based on the reported molecular ferroelectric [2.2.2-dabco]BF4 (2.2.2-dabco = 1,4-diazabicyclo[2.2.2]octonium) with an Aizu notation of 4/mmmFmm2 and two polar axes, we changed the [2.2.2-dabco]+ cation to the [3.2.1-dabco]+ cation for reducing the molecular symmetry and ke...