Ferroelastic phase transitions in three new layered perovskites: (3-XC6H5CH2CH2NH3)2[CdCl4] (X = F, Cl, and Br)

Two-dimensional organic-inorganic hybrid ferroelastics with high-temperature reversible phase transitions are very rare and have become one of the research hotspots in the field of ferroelastic materials. Herein, we report three new layered organic-inorganic hybrid perovskites based on halogen-substituted phenethylaminium, (3-XC6H5CH2CH2NH3)2[CdCl4] (X = F (1), Cl (2) and Br (3)). They undergo structural phase transitions at 376/371 K, 436/430 K, and 421/411 K, respectively, between the isomorphic high-temperature phases (space group I4/mmm, Z = 2) and different room-temperature phases with the reduced structural symmetries, i.e., P21/a (Z = 2) in 1, P1¯ (Z = 4) in 2, and P21/a (Z = 4) in 3, respectively. These ferroelastic transitions arise from the order-disorder transition of organic cations together with the synchronous displacement of inorganic layers, accompanying with ferroelastic spontaneous strains of 0.16, 0.13 and 0.12 for 1−3, respectively. By enriching layered perovskite ferroelastics based on halogen-substituted cations, this work provides important clues for exploring new ferroic materials based on hybrid crystals.