Structure and ferroelectric properties of (C3N2H5)5Bi2Cl11 -: art. no. 104107

Pentakis (imidazolium) undecachlorodibismuthate(III), (C3N2H5)(5)Bi2Cl11, 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 P2(1)/n with a=13.616 A, b=14.684 A, c=9.045 A, and beta=96.85 degrees. Two solid-solid phase transitions: P (4) over bar n2 ->(360 K)P2(1)/n (I -> II), and P2(1)/n ->(166 K)P2(1) (II -> 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 K and saturated spontaneous polarization value of the order of 6x10(-3) C m(-2) along the 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.