Thermal stability, cation dynamics, and ferroelastic domain walls in the α→β→γ phase transitions of perovskite (C2H5NH3)2MnCl4 crystals

Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed that the (C2H5NH3)(2)MnCl4 crystal undergoes alpha-beta-gamma phase transitions at approximately T-C2 = 225 K and T-C1 = 424 K, remains stable until 470 K, and displays a weight loss of 25.24% at around 579 K due to partial thermal decomposition. Cation dynamics near these temperatures was investigated by MAS H-1 NMR and MAS C-13 NMR experiments. The small changes in the H-1 chemical shift for C2H5 near T-C2 are consistent with the transition from the orthorhombic gamma-phase to the orthorhombic beta-phase. Also, the abrupt changes in NMR signals near T-C1 correspond to structural change from the orthorhombic beta-phase to the tetragonal alpha-phase. The C-13 spin-lattice relaxation time in the rotating frame (T-1 rho) below T-C2 is shorter for CH3 than that for CH2, due to the greater mobility at the free end of the alkyl chain. In addition, the temperature-dependent ferroelastic domain structure was studied near the alpha-beta phase transition. There was no noticeable temperature dependence in H-1 and C-13 T-1 rho values at T-C1 and T-C2, whereas the change in the domain wall was prominent near T-C1.