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

Graphical A modern material : A novel high-temperature host-guest inclusion ferroelectric, [(C 6 H 5 NF 3 )(18-crown-6)][BF 4 ], has successfully been synthesized; it underwent a reversible structural phase transition around T c =348 K, with a wide band gap of 4.43 eV. The chief contributors to this are the C, H and O atoms of the crystals, the obvious second harmonic generation response and the large value of spontaneous ferroelectric polarization of around 4.06 μC/cm 2 . Molecular ferroelectrics of high-temperature reversible phase transitions are very rare and have attracted increasing attention in recent years. In this paper is described the successful synthesis of a novel high-temperature host-guest inclusion ferroelectric: [(C 6 H 5 NF 3 )(18-crown-6)][BF 4 ] ( 1 ) that 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 measurements, thus indicating that 1 undergoes a reversible structural phase transition. 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. In its semiconducting properties, 1 shows a wide optical band gap of about 4.43 eV that comes chiefly from the C, H and O atoms of the crystals. In particular, the ferroelectric measurements of 1 exhibit a typical polarization-electric hysteresis loop with a 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.