Ferroelectric properties of [4-NH2C5H4NH][SbCl4] -: art. no. 024103

A ferroelectric crystal [4-NH2C5H4NH][SbCl4] has been synthesized. The x-ray diffraction studies indicate that it is made of polyanionic chains of (SbCl4-)(n) forming a tunnel-like structure and the 4-aminopyridinium cations connected via weak hydrogen bonds to the chlorine atoms. The x-ray and differential scanning calorimetry studies show that the crystal undergoes a complex sequence of phase transitions: P2(1)/c<---->(240/245 K)(Cc)<---->(248.5/250 K) Cc<---->(270.5/271 K)C2/c<---->(304/304 K)C2/c. The pyroelectric measurements reveal that [4-NH2C5H4NH][SbCl4] becomes ferroelectric below 270.5 K with the spontaneous polarization of the order of 3.5 mC/m(2) measured along the [102] direction. The dielectric results confirm the order-disorder nature of the paraelectric-ferroelectric phase transition. The dynamics of the 4-aminopyridinium cations plays an essential role in the ferroelectric phase transition mechanism.