Dilatometric, dielectric and NMR studies of structural phase transitions of the (CH3NH3)(3)Bi2Cl9 (MACB) crystals

The phase transitions and molecular motions of the methylammonium cations were investigated in the (CH3NH3)(3)Bi2Cl9 (MACE) crystal by dilatometric and dielectric measurements, and by the measurements of the H-1 spin-lattice relaxation times and second moment of the H-1 NMR absorptions over a wide temperature range. Structural phase transitions, weakly first order at 247 K (III <----> II) and continuous at 352 K (II <----> I), were detected by the dilatometric technique. The H-1 NMR measurements revealed the presence of the uniaxial reorientations of the three non-equivalent methylammonium cations in the lowest temperature phase (III).