Structure and ferroelectric properties of(C3N2H5)5Bi2Cl11

Abstract

Pentakis (imidazolium) undecachlorodibismuthate(III), ${({\mathrm{C}}_{3}{\mathrm{N}}_{2}{\mathrm{H}}_{5})}_{5}{\mathrm{Bi}}_{2}{\mathrm{Cl}}_{11}$, has been synthesized and studied by means of the x-ray, differential scanning calorimetry (DSC), and dielectric methods over a wide temperature range. The room temperature crystal structure has been determined as monoclinic, space group $P{2}_{1}∕n$ with $a=13.616\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $b=14.684\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $c=9.045\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, and $\ensuremath{\beta}=96.85\ifmmode^\circ\else\textdegree\fi{}$. Two solid--solid phase transitions: $P\overline{4}n2\stackrel{360\phantom{\rule{0.3em}{0ex}}\mathrm{K}}{\ensuremath{\rightarrow}}P{2}_{1}∕n$ $(I\ensuremath{\rightarrow}II)$, and $P{2}_{1}∕n\stackrel{166\phantom{\rule{0.3em}{0ex}}\mathrm{K}}{\ensuremath{\rightarrow}}P{2}_{1}$ $(II\ensuremath{\rightarrow}III)$, discontinuous and continuous in nature, respectively, have been revealed. The dielectric and pyroelectric measurements allow us to characterize the lowest temperature phase (III) as ferroelectric with the Curie point at $166\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and saturated spontaneous polarization value of the order of $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\mathrm{C}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$ along the $\mathbit{b}$ axis. The ferroelectric phase transition mechanism is governed by the dynamics of imidazolium cations. The room temperature, paraelectric phase (II) demonstrates additionally the ferroelastic properties.