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)BiCl 5 and (n-C4H9NH3)(3) SbCl6 by means of differential scanning calorimet ry, dilatometric and dielectric dispersion (1 kHz-1 MHz) studies. For the transitions the basic thermodynamic data are determined. Interesti ng dielectric properties are found in a metastable (beta) form of the (n-C4H9NH3)(2)BiCl5 crystals. Debye-like dispersion of the electric pe rmittivity between 30 and 800 MHz is observed around the 310 K phase t ransition for this crystal. The activation energy of the reorientation of the n-butylammonium cations is found to be 16 kJ mol(-1). The stru cture of(n-C4H9NH3)(2)BiCl5 (alpha form) has been refined to R = 0.043 9 and shows isolated Bi2Cl104- units and two non-equivalent n-butylamm onium units. One of these cation possesses dynamical disorder. Most of the phase transitions in the title crystals are classified as an 'ord er-disorder' type and connected with a reorientational motion of the n -butylammonium cations.