Ferroelectric properties of (C5H5NH)5Bi2Br11

A new pyridinium compound, (C5H5NH)(5)Bi2Br11, has been synthesized. The x-ray diffraction studies indicate that its structure is built up of four independent pyridinium cations and isolated Bi2Br115- groups. At room temperature it crystallizes in the monoclinic space group P2(1)/n. Two phase transitions of second- and first-order type are detected by the differential scanning calorimetry measurements at 118 and 405/403 K (on heating-cooling), respectively. The corresponding anomalies in the linear thermal expansion at 118 and 405 K are observed along three crystallographic directions. The dielectric investigations reveal dielectric absorption and dispersion in the radio-frequency region. The experimental results were analyzed on the basis of dielectric formula which represents the sum of two independent relaxators. The pyroelectric measurements reveal that (C5H5NH)(5)Bi2Br11 becomes ferroelectric below 118 K and is characterized by the appearance of spontaneous polarization of the order of 3.10(-3) C/m(2) along the b axis. (C) 2001 American Institute of Physics.