Ferroelectric properties of [4-NH2C5H4NH][SbCl4]

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: P21/c(subform(↔))(lim((bu(240/245 K))))(Cc)(subform(↔))top-tag(248.5/250 K)top-tagCc(subform(↔))top-tag(270.5/271 K)top-tagC2/c(subform(↔))top-tag(304/304 K)top-tagC2/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/m2 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