Synthesis,structure And Ferro-dielectric Properties Of Aromatic Ammonium Metal Halides And Crown Ether Inclusion Compounds

Molecular ferro-dielectric reversible phase-transition materials have attracted much attention in recent years owing to their reasonable design,good mechanical flexibility,structural diversity,light weight,environmental friendliness and ease of synthesis.The reason for research interest in this class of materials is not only in the above-mentioned advantages,but also in their forward-looking technological applications in many fields such as energy and data storage devices,signal processors,sensors,actuators,switchable dielectric devices and nonlinear optics.In this thesis,a total of eight multifunctional ferro-dielectric crystals possessing high temperature phase transition have been successfully synthesized by solution method.Through a series of abundant characterization methods,the structure,thermodynamic-optical and ferro-dielectric properties of the compounds have been researched.The main contents of this thesis are as follows:（1）Employing the organic amine of flexible 2-（2-chlorophenyl）ethylamine as the organic cation ligand,and rationally replacing the central metal cation in the inorganic framework,three organic-inorganic hybrid compounds[Cl-C₆H₄-（CH₂）₂NH₃]₂Cu Br₄（1）,[Cl-C₆H₄-（CH₂）₂NH₃]₂Cd Br₄（2）and[Cl-C₆H₄-（CH₂）₂NH₃]₃Sb Br₆（3）have been successfully synthesized,undergoing high-temperature reversible structural phase transitions around 355 K/335 K/368 K,respectively.With the replacement of metal cations,the crystal system and dimensionality,phase-transition temperature,and thermal stability exhibit significant changes.Particularly,compound 1 also shows variable-temperature luminescence intensity,and long fluorescence lifetime of 55.46μs in optical properties.（2）Through the rational adjustment and modification of the inorganic architecture,the transformation inorganic anions from[Cu Cl₄]^2--[Cd Cl₄]^2--[Bi Cl₅]^2-and introduction of the flexible 2-（4-methoxyphenyl）ethanamine.Three unusual high-temperature phase transition compounds[H₃CO-C₆H₄-（CH₂）₂NH₃]₂Cu Cl₄（4）,[H₃CO-C₆H₄-（CH₂）₂NH₃]₂Cd Cl₄（5）and[H₃CO-C₆H₄-（CH₂）₂NH₃]₂Bi Cl₅（6）have been found,which experiences reversible structural phase transitions around 385 K/390 K/409 K.When the central metal cation of inorganic framework changing from left to right in the periodic table,namely Cu²⁺-Cd²⁺-Bi³⁺,not only the dimension of the compounds decreases,but also the phase-transition temperature increases gradually.In addition,the entropy change,thermal stability,and dielectric property have all been significantly transformed.（3）Via rationally adjusting and modifying organic cations,that is,replacing the position of fluorine atoms on organic amines,two novel stator-rotor crown ether inclusions[（C₆H₅NF₃）（18-crown-6）][BF₄]（7）;（8）,have been successfully constructed.Room-temperature compound 7 crystallized in the centrosymmetric space group P2₁/c,and compound 8 crystallized in the ferroelectric space group Pca2₁ after adjusting the position of the fluorine atom on the benzene ring,undergoing high-temperature reversible phase transition around 364 K/348 K,respectively.Compound 7 exhibits strong fluorescence emission with a fluorescence lifetime of 43.998μs.Compound 8shows excellent ferroelectric property and nonlinear second-harmonic response at room temperature,and its saturated spontaneous polarizability is as high as 4.06μC/cm²,which is about 16 times larger than that of the first ferroelectric Rochelle salt（0.25μC/cm²）.