Refined Analysis of the Crystal Structure, Thermodynamic Property, and Structural Geometry of Perovskite (CH₃NH₃)₂ZnBr₄

Organic-inorganic hybrid single crystals of (CH₃NH₃)₂ZnBr₄ were grown by the aqueous solution technique, and their structure, phase transition temperature, and thermal stability were discussed. The crystals were determined to have a monoclinic structure using X-ray diffraction on single crystals, and a transition temperature of 458 K was confirmed from the differential scanning calorimetry and X-ray diffraction analyses on powders. Moreover, the compound exhibited excellent thermal stabilities up to 550 K. The ¹H and ¹³C nuclear magnetic resonance chemical shifts of CH₃ shifted in the positive direction as the temperature increased, while the ¹H chemical shift of NH₂ exhibited minor variations in N-H···Br hydrogen bonding, which was influenced by minor changes in the bromide ions surrounding Zn in the ZnBr₄ anion. The spin-lattice relaxation time, which indicates the energy transfer near ¹H and ¹³C, exhibited similar values, which is because ¹H and ¹³C are bonded to each other in the CH₃NH₃ cation. This compound exhibits high structural and thermal stabilities and is expected to pave the way for future applications.