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

Abstract

Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed that the (C2H5NH3)2MnCl4 crystal undergoes α-β-γ phase transitions at approximately TC2 = 225 K and TC1 = 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 1H NMR and MAS 13C NMR experiments. The small changes in the 1H chemical shift for C2H5 near TC2 are consistent with the transition from the orthorhombic γ-phase to the orthorhombic β-phase. Also, the abrupt changes in NMR signals near TC1 correspond to structural change from the orthorhombic β-phase to the tetragonal α-phase. The 13C spin-lattice relaxation time in the rotating frame (T1ρ) below TC2 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 α-β phase transition. There was no noticeable temperature dependence in 1H and 13C T1ρ values at TC1 and TC2, whereas the change in the domain wall was prominent near TC1.