Crystal structure and dielectric relaxation studies of the [N(CH3)3H]3Sb2(1-x)Bi2xCl9 mixed crystals

The influence on ferroelectric properties of a partial substitution of antimony by bismuth in the [N(CH3)(3)H](3)Sb2Cl9 (TMACA) crystals are investigated by dielectric and x-ray diffraction methods. The dielectric relaxation in the [N(CH3)(3)H](3)Sb2(1-x)Bi2xCl9 (TMACAB) mixed crystals (x = 0, 0.07, 0.33, 0.38, and 1) is studied in the frequency range between 20 Hz and 1 GHz and temperature range between 170 and 375 K. The ferroelectric properties of mixed crystals are preserved for the Bi concentration less than 0.33. The increase of the Bi concentration distinctly influences the phase transition temperature but only weakly the dynamical properties of those crystals. The dielectric response of the ferroelectric TMACAB crystals is characterized by a presence of two relaxation modes. One of them behaves critically and the other one is only thermally activated. The disappearance of ferroelectric properties is connected with the essential change of crystal structure of mixed compounds. The anionic sublattice of nonferroelectric TMACAB (x > 0.33) (<R(3)over bar>c space group) instead of two-dimensional layers is composed of the isolated Sb2(1-x)Bi2xCl9 bioctahedral units. (C) 2000 American Institute of Physics. [S0021-8979(00)02214-3].