A new organic ferroelectric compound, 4-(cyanomethyl)anilinium perchlorate, proceeds a second-order phase transition from a paraelectric phase ($P{2}_1/m$) to a ferroelectric phase ($P{2}_1$) 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 $-{\mathrm{NH}}_3^{+}$ cations and ${\mathrm{ClO}}_4^{-}$ anions from the symmetric positions including a small part of the order-disorder behaviors of the ${\mathrm{ClO}}_4^{-}$ anions.

• Received 8 May 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.147601