Halogen Substitution in Inorganics for the Regulation of Phase Transition Temperature in Zero-Dimensional Organic-Inorganic Hybrid Metal Halide Dielectric Switching Materials
摘要
Zero-dimensional (0D) organic-inorganic hybrid metal halide material (OIMH) [C3H6NH2]2CoBr4 (C3H6NH2 = azetidine cation) was successfully synthesized and carried out a series of characterizations. A comparison with [C3H6NH2]2CoCl4 was then conducted. It was found that after the anionic halogen substitution, the dielectric switching properties remained essentially consistent, and the main reason for the phase transition was the cationic order-disorder motion. However, the phase transition temperature (TC) of [C3H6NH2]2CoBr4 is 364.5 K, which is 16.8 K higher than that of [C3H6NH2]2CoCl4. Calculations revealed that the void occupancy between cations and anions decreased from 32.49% in [C3H6NH2]2CoCl4 to 29.77% in [C3H6NH2]2CoBr4, and due to the reduction in porosity, the temperature required for cationic order-disorder motion is therefore higher. Additionally, the analysis of the Hirshfeld surface and two-dimensional fingerprints revealed that the proportion of intermolecular hydrogen bond interactions in [C3H6NH2]2CoBr4 (47.1%) is higher than in [C3H6NH2]2CoCl4 (45.75%), and there is also an enhancement in the non-covalent interaction energies between cations and anions (the non-covalent interaction energies between cations and anions in [C3H6NH2]2CoCl4 are –6.9 and –8.7 kJ/mol, while in [C3H6NH2]2CoBr4 they are –7.6 and –20.9 kJ/mol, which is also the reasons for the increase in TC. Furthermore, we observed that as the volume of anions in the inorganic framework increased, the band gap value also showed a decreasing trend, from 4 eV for [C3H6NH2]2CoBr4 to 3.678 eV for [C3H6NH2]2CoCl4.