Phase transitions in (CH3NH3)3Bi2Cl9 studied by calorimetric, X-ray diffraction and dielectric methods

Differential scanning calorimetry studies revealed two phase transitions in (CH3NH3)3Bi2Cl9 at Tc1-349 K and Tc2 = 247 K. X-ray diffraction and dielectric investigations showed only one anomaly at Tc1 = 349 K related, most probably, to the motion of methylammonium cations. The high temperature phase (above Tc1) behaves as a plastic phase with disordered cations. This high temperature phase is orthorhombic with a contraction along the a-axis and an expansion along the b and c axes compared with the room temperature phase.