4-(cyanomethyl)anilinium Perchlorate: A New Displacive-Type Molecular Ferroelectric

A new organic ferroelectric compound, 4-(cyanomethyl) anilinium perchlorate, proceeds a second-order phase transition from a paraelectric phase (P2(1)/m) to a ferroelectric phase (P2(1)) at 184 K. A perfect ferroelectric hysteresis loop was observed even at 10 KHz. It is the first example of a molecule-based organic ferroelectric whose polarization can be switched at such a high frequency. The temperature dependent second harmonic generation effect shows that the second-order nonlinear coefficient is nearly zero above T-c and proportional to the spontaneous polarization below T-c, suggesting the occurrence of symmetry breaking, in good agreement with crystal structural determination. The origin of ferroelectricity was ascribed to the displacements of -NH3+ cations and ClO4- anions from the symmetric positions including a small part of the order-disorder behaviors of the ClO4- anions.