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.