Dilatometric, dielectric and NMR studies of structural phase transitions of the (CH 3NH 3) 3Bi 2Cl 9 (MACB) crystals

Abstract

The phase transitions and molecular motions of the methylammonium cations were investigated in the (CH 3NH 3) 3Bi 2Cl 9 (MACB) crystal by dilatometric and dielectric measurements, and by the measurements of the 1H spin-lattice relaxation times and second moment of the 1H 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 1H NMR measurements revealed the presence of the uniaxial reorientations of the three non-equivalent methylammonium cations in the lowest temperature phase (III).