Design,Synthesis And Properties Of Organic-metal Halide And Ammonium-based Compounds Phase Transition Materials

Structural phase transition crystal materials often have novel and unique properties in force,electricity,light,heat,magnetism,etc.And have a wide range of applications in related shape memory materials,superelastic materials,superconductor materials,semiconductor materials,dielectric switch materials,nonlinear switches materials,electrothermal materials,magnetic materials and other aspects.The switching materials can quickly change the switching state under the stimulation of the corresponding external conditions.It is worth noting that nonlinear response switch materials have been extensively studied as a special molecular switch.From the symmetry of the structure,only the material crystallizes in a specific point group,and the corresponding physical properties are exhibited.For example,the second-order nonlinearity can only appear in 18 non-central symmetric（NCS）point groups C₁,C₂,C_1h,D₂,D_2v,C₄,S₄,C_4v,D_2d,C₃,D₃,C_3v,C₆,C_3h,C_6v,D_3h,T,T_d,the availability and strength of the signal are closely related to the symmetry of the crystal and its own characteristics.In order to design this special phase change material,two kinds of compound materials were selected for study:（1）Construction of compounds with trivalent cyclic amines as ligands.Such crystal materials are prone to occur as ferroelectric phase transitions of crown ether ring compounds and are prone to become donors in the formation of abundant hydrogen bonds,increasing the probability of compounds crystallize in polar space groups,and the stability of the molecular structure is increased,which provides a possibility for high temperature reversible phase transition;（2）Organic-inorganic hybrid materials.The crystal material has the advantages of easy modification,light weight,good mechanical flexibility and environmental protection in the processing.Therefore,it is receiving more and more attention in many fields such as,aerospace,information,and new energy.Based on cyclic amine and organic-metal halide framework,phase change materials with NLO switch,dielectric switch,dielectric relaxation,semiconductor,strong photoconductivity and other properties were designed and synthesized,and their structure,phase transition and related physical properties were characterized and studied.（I）In Chapter Two,ferroelectric[（CH₃）₃NCH₂Cl]-CdCl₃ was used as a design reference to synthesize[（CH₃）₃NCH₂Cl]-ZnCl₃（1）and[（CH₃）₃NCH₂Cl]₂-ZnCl₄（2）.Compound 2 has switchable nonlinear optical（NLO）and dielectric properties around258 K,and its NLO and dielectric switch switching have good fatigue resistance.（II）In Chapter Three,based on the organic ion phase change compound[9-tacn-3]·3[Cl]（3）,successfully synthesized compound[9-tacn-3]·[BF₄]·2[Cl]（4）,with NLO switch and dielectric switching properties near as high as 400 K.（III）In Chapter Four,based on the compound[（CH₃）₄N]₂-ZnBr₄（5）,the compound[（CH₃）₃NCH₂Br]₂-ZnBr₄（6）with high temperature ferroelastic phase transition was designed and synthesized.In the process of temperature increase and decrease around 387 K,the disappearance and recombination of the strip domains can be observed.（IV）In Chapter Five,Synthesis of organic-metal halide semiconductor materials[NH₃CH（CH₃）（CH₂）₄NH₃]₂-SbCl₅（7）,[NH₃CH（CH₃）（CH₂）₄NH₃]₂-SbBr₅（8）,[NH₃CH（CH₃）（CH₂）₄NH₃]₂-SbI₅（9）,[NH₃CH（CH₃）（CH₂）₄NH₃]₂-BiCl₅（10）,[NH₃CH（CH₃）（CH₂）₄NH₃]₂-BiBr₅（11）and[NH₃CH（CH₃）（CH₂）₄NH₃]₂-BiI₅（12）,in which the solid-state UV-vis diffuse reflectance spectra of compounds 7 to 12 showed significant absorption at about 370nm,500 nm,650 nm,460 nm,490 nm and 660 nm,respectively.The absorption and estimated band gaps are 3.58 eV,2.60 eV,1.92 eV,3.02 eV,2.63 eV,and 1.93 eV,respectively,and the main contribution is derived from the inorganic MX₅（M=Sb,Bi;X=Cl,Br,I）skeleton.In addition,Compound 9 also has a strong photoconductive effect.Further comparative studies have found that in[NH₃CH（CH₃）（CH₂）₄NH₃]₂-MX₅（M=Sb,Bi;X=Cl,Br,I）semiconductor crystals,the band gap（E_X）is E_C1>E_Br>E_I.Interestingly,Compound 9 to 12 observed a significant dielectric relaxation phenomenon over a wide temperature range.