On structural phase transitions in n-butylammonium chloroantimonate(III) and chlorobismuthate(III) crystals: X-ray, differential scanning calorimetry, dilatometric and dielectric dispersion studies

Numerous structural phase transitions are detected in new crystals of the n-butylammonium compounds: (n-C4H9NH3)(2)SbCl5, (n-C4H9NH3)(2)BiCl5 and (n-C4H9NH3)(3) SbCl6 by means of differential scanning calorimetry, dilatometric and dielectric dispersion (1 kHz-1 MHz) studies. For the transitions the basic thermodynamic data are determined. Interesting dielectric properties are found in a metastable (beta) form of the (n-C4H9NH3)(2)BiCl5 crystals. Debye-like dispersion of the electric permittivity between 30 and 800 MHz is observed around the 310 K phase transition for this crystal. The activation energy of the reorientation of the n-butylammonium cations is found to be 16 kJ mol(-1). The structure of(n-C4H9NH3)(2)BiCl5 (alpha form) has been refined to R = 0.0439 and shows isolated Bi2Cl104- units and two non-equivalent n-butylammonium units. One of these cation possesses dynamical disorder. Most of the phase transitions in the title crystals are classified as an 'order-disorder' type and connected with a reorientational motion of the n-butylammonium cations.