High-Temperature and Large-Polarization Ferroelectric with Second Harmonic Generation Response in a Novel Crown Ether Clathrate.

Abstract

Molecular ferroelectrics of high-temperature reversible phase-transition are very rare and have attracted increasing attention in recent years. In this paper, we have successfully synthesized a novel high-temperature host-guest inclusion ferroelectric: [ (C 6 H 5 NF 3 ) (18-crown-6)][BF 4 ] (1) , which shows a pair of reversible peaks at 348 K (heating) and 331 K (cooling) with a heat hysteresis about 17 K by differential scanning calorimetry (DSC) measurements, indicating that 1 undergoes a reversible structural phase transition. The variable-temperature PXRD and temperature-dependent dielectric measurements further prove the phase-transition behavior of 1 . The second harmonic response demonstrates that 1 belongs to a non-centrosymmetric space group at room temperature and is a good nonlinear optical material. Meanwhile, 1 shows a wide optical band gap of about 4.43 eV in semiconducting property and is chiefly contributed by C, H and O atoms of the crystals. In particular, the ferroelectric measurements of 1 exhibit a typical polarization-electric hysteresis loop with large spontaneous polarization ( P s ) of about 4.06 μC/ cm 2 . This finding offers an alternative pathway for designing new ferroelectric-dielectric and nonlinear optical materials and related physical properties in organic- inorganic and other hybrid crystals.