Figure 3.
FASnI3 undergoes two phase transitions in the temperature range from 300 to 85 K. a,b) The cubic phase at room temperature contains fully rotationally disordered FA molecules. c,d) The structure becomes tetragonal at 255 K because of an in‐plane rotation of the SnI6 octahedra. The orientation of the FA molecules is two‐fold disordered due to mirror planes (shaded light blue). e,f) Doubling of the c‐lattice parameter occurs at 155 K, as the mirror planes perpendicular to the c–axis are removed and the FA molecules become fully ordered. There are now two distinct layers of SnI6 octahedra with different rotation angles. a–f) Reproduced with permissio.[ 55 ] Copyright 2020, American Chemical Society.