Synthesis,Structure And Properties Of Organic-Inorganic Hybrid Copper-Based Halide Phase Transition Materials

Organic-inorganic hybrid metal halide phase transition materials show promising applications in optoelectronics,sensing,catalysis,luminescence,and other fields due to their diverse structures and unique properties,such as sensors,energy storage and so on.Among them,lead halides have been extensively investigated for their excellent optoelectronic properties.However,lead has a serious environmental pollution problem,which limits its practical application.Therefore,it is important to find excellent lead-free and non-toxic metal halides.Among many lead-free metal halide hybrids,copper halides have become a popular alternative material to replace lead halide due to its advantages of abundant reserves,low cost,and non-toxicity.The work focuses on organic-inorganic hybrid copper halide phase transition materials,taking copper as the central metal element and halogen as the coordination anion,to study the functional group of changing template cation,replacing the metal halide ligand and replacing the cation based on"quasi-spherical theory".In this thesis,nine new organic-inorganic hybrid copper-based halides were synthesised.The main findings include:[C₇H₁₄N]₂CuCl₄(C₇H₁₄N=protonated quinuclidine)（1）,[C₇H₁₄N]₂Cu Br₄（2）have been prepared by using spherical amine to undergo phase transition under temperature stimulation.The results show that compound 1 exhibits an interesting high-temperature ferroelastic phase transition at 353 K,while compound 2,which is only different from compound 1 in halogen,exhibits two dielectric switching properties near 296 K and 398 K,respectively.Therefore,the halogen coordination anion has an important influence on the physical properties of the compound.According to the"quasi-spherical theory",[C₇H₁₂NO]₂Cu Cl₄（3）,[C₇H₁₂NO]₂Cu Br₄（4）,[C₇H₁₄N-OH]₂Cu Cl₄（5）,[C₇H₁₄N-OH]₂Cu Br₄（6）,[R-C₇H₁₄N-OH]₂Cu Cl₄（7）,[R-C₇H₁₄N-OH]₂Cu Br₄（8）were successfully prepared by replacing the functional groups,from ketone carbonyl to alcoholic hydroxyl group to chiral alcoholic hydroxyl group and replacing the anionic ligand halogen bond.The results show that compound 5,6,7 and 8 exhibited obvious reversible phase transition characteristics under the effect of temperature,and all showed dielectric anomalies near the phase transition point.Compared with compound 3 and 4,phase transition materials 5 and 6 were successfully obtained by replacing the functional groups with enhanced electronegativity.Two ferroelectrics were prepared by introducing chiral groups into compound 7 and 8 compared with compound 5 and 6.The results indicate that replacing of functional groups is an effective strategy for the design of phase transition materials.The[C₇H₁₆N]₂CuBr₄（9）was successfully prepared by further altering the template cation.Unlike compounds 1～8,compound 9 features a two-dimensional perovskite.Compound 9 is found be an ideal indirect band-gap semiconductor（1.06 eV）with obvious dielectric aberration near the phase transition temperature.The X-ray probe photoelectric response switching ratio prepared by the single crystal film reaches 91.8 and the dark current is as low as 0.11 p A,which is expected to have potential applications in X-ray detectors.This study shows that the structure and phase transition properties can be regulated by substituting metal halide ligands or modifying organic cations.It provides a new strategy to design more organic-inorganic hybrid metal halide materials with superior properties and novel structures.