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: [(C₆H₅NF₃)(18-crown-6)][BF₄] (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/cm². 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.

中文翻译：

---

新型冠醚包合物中具有二次谐波发生响应的高温大极化铁电体

高温可逆相变的分子铁电体非常罕见，近年来受到越来越多的关注。本文描述了一种新型高温主客体包裹体铁电体的成功合成：[(C ₆ H ₅ NF ₃ )(18-crown-6)][BF ₄ ] ( 1 )通过差示扫描量热法测量，在 348 K（加热）和 331 K（冷却）处达到峰值，热滞后约为 17 K，因此表明1经历了可逆的结构相变。变温 PXRD 和随温度变化的介电测量进一步证明了1. 二次谐波响应表明，1在室温下属于非中心对称空间群，是一种良好的非线性光学材料。在其半导体特性方面，1显示出大约 4.43 eV 的宽光学带隙，主要来自晶体的 C、H 和 O 原子。特别地，铁电测量1显示出具有大的自发极化（典型的偏振电滞回线P_小号的约4.06μC）/厘米²。这一发现为设计新的铁电介质和非线性光学材料以及有机-无机和其他混合晶体的相关物理特性提供了另一种途径。