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.