Properties and structural phase transitions of (CH3NH3)3Sb2I9

Abstract The tris (methylammonium) nonaiododiantimonate (III) crystals were grown. The preliminary X-ray diffraction studies showed that at room temperature they are isomorphous with Cs3Sb2I9. The crystals are hexagonal, space group P63/mmc with the unit cell parameters; a = 8.543 (1), c = 21.520 (7) a, Z = 2, V = 1360 A3. The DSC studies revealed two structural phase transitions at T c1 = 147 K, and T c2 = 111 K. The dielectric studies showed only one anomaly at T c1 = 147 K. The high temperature phase behaves like a plastic one with respect to a freedom of rotational motions of methylammonium cations. The dielectric and pyroelectric properties seem to indicate antiferroelectric ordering below T c1.