Dielectric and Pyroelectric Studies on [N(CH$\text{}_{3}$)$\text{}_{4}$]$\text{}_{3}$Bi$\text{}_{2}$X$\text{}_{9}$ (X = Cl, Br)

Dielectric properties of [N(CH$\text{}_{3}$)$\text{}_{4}$]$\text{}_{3}$Bi$\text{}_{2}$X$\text{}_{9}$ (X = Cl, Br) single crystals were measured in the frequency range 1 kHz - 1 MHz in the vicinity of structural phase transitions of first-order type at 152 K (Cl) and 183 K (Br). The pyroelectric effect was observed in [N(CH$\text{}_{3}$)$\text{}_{4}$]$\text{}_{3}$Bi$\text{}_{2}$[N(CH$\text{}_{3}$)$\text{}_{4}$]$\text{}_{3}$Bi$\text{}_{2}$Cl$\text{}_{9}$ at structural phase transition (T$\text{}_{c}$ = 152 K) with the ΔP$\text{}_{s}$ of the order of 10$\text{}^{-5}$ C m$\text{}^{-2}$. Polarized microscope observations show appearance of ferroelectric domain structure in [N(CH$\text{}_{3}$)$\text{}_{4}$]$\text{}_{3}$Bi$\text{}_{2}$Br$\text{}_{9}$ within the low temperature phase.