Data for: The Ferroelectric Properties of 4-Aminopyridinium Perchlorate

4-Aminopyridinium Perchlorate (APP), used to be known as a pyroelectric below 243K, is first discovered to be a new molecular ferroelectric in this work, which has a perfect electric hysteresis loops with a large spontaneous polarization of 1.0 mC/cm2 and a small coercive field of 0.67 kV/cm below 244.5 K. As shown in XRD,owing to the dramatic changes of the protonated cations and order-disorder of anions, the crystal symmetry of APP transforms from P21/c to P21 in this first-order phase transition, which is revealed by other measurements, such as differential scanning calorimetry, dielectric anomalies and Raman spectrum.Due to the lowing of the symmetry from the ideal tetrahedral geometry, splittings can be observed for the doubly degenerate modes. The modes of 405 cm-1 at 203 K were fitted by Gaussian functions.The symmetric stretching vibration at 405 cm-1 breaks up into two bands (402 cm-1, 408 cm-1) below transition temperature.高氯酸4-氨基吡啶鎓（4-Aminopyridinium Perchlorate，APP）曾被认为在243K以下具有热释电性，本研究首次发现其为一种新型分子铁电体。该材料在244.5K以下可展现出完美的电滞回线，自发极化强度达1.0 mC/cm²，且矫顽场仅为0.67 kV/cm。如X射线衍射（X-ray Diffraction，XRD）结果所示，受质子化阳离子的剧烈变化与阴离子有序-无序转变的影响，APP的晶体对称性在该一级相变过程中由P2₁/c转变为P2₁，这一结论通过差示扫描量热法、介电异常及拉曼光谱等多种测试手段得以验证。由于对称性相较于理想四面体构型有所降低，二重简并振动模式可观测到分裂现象。203K下位于405 cm⁻¹的振动模式通过高斯函数进行拟合；在相变温度以下，原本位于405 cm⁻¹的对称伸缩振动峰分裂为402 cm⁻¹与408 cm⁻¹两个子峰。