Ferroelectric properties of (C_5H_5NH)_5Bi_2Br_11

摘要

A new pyridinium compound, (C_5H_5NH)_5Bi_2Br_11, has been synthesized. The x-ray diffraction studies indicate that its structure is built up to four independent pyridinium cations and isolated Bi_2Br_11~(5-) groups. At room temperature it crystallizes in the monoclinic space group P2_1. 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 crystallographic directions. The dielectric investigations reveal dielectric absorption and dispersion in the ratio-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 (C_5H_5NH)_5Bi_2Br_11 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.