Study on structural geometry and dynamic property of [NH₃(CH₂)₅NH₃]CdCl₄ crystal at phases I, II, and III

Organic-inorganic hybrid perovskites can potentially be used in electrochemical devices, such as batteries and fuel cells. In this study, the structure and phase transition temperatures of the organic-inorganic material [NH₃(CH₂)₅NH₃]CdCl₄ crystal were confirmed by X-ray diffraction and differential scanning calorimetry. From the nuclear magnetic resonance results, the crystallographic configurations of ¹H, ¹³C, and ¹⁴N in the cation changed at temperatures close to T_C1 (336 K), whereas that of ¹¹³Cd in the anion shows significant changes at temperatures close to T_C1 and T_C2 (417 K). The activation energy, E_a, values for ¹H and ¹³C obtained from the spin-lattice relaxation time, T_1ρ, below and above T_C1 were evaluated, where the E_a value for ¹³C was more flexible at low temperatures than at high temperatures. In addition, the effect on molecular motion was effective at high temperatures. The phase transition at 336 K was associated with the change in the N-H···Cl bond due to the change in the coordination geometry of Cl around Cd in the CdCl₆ anion. On the other hand, the phase transition at 417 K was related to the ferroelastic phase transition attributed to the twin domains.