The Synthesis,Dielectric,Conductivie And Ferroelectric Properties Research Of Organic-Inorganic Hybrid Perovskite Phase Transition Materials

Phase transition materials with organic-inorganic hybrid perovskite structure,especial for the ferroelectric materials,have wide application prospects in data storage?photoconductive semiconductor materials and optoelectronic switch,due to their excellent ferroelectric?piezoelectric and nonlinear optical properties.In order to improving properties,some of methods were used to design and synthesis molecule-based compounds,including mixed cations?metal doping and composite of materials.In this thesis,we have chosen different organic amines to synthesize organic-inorganic hybrid perovskite compounds by mixed cations and epitaxial growth methods.Phase transition?dielectric?conductive and ferroelectric properties of synthesized compounds were researched,the main results are as follows:1.Six organic-inorganic hybrid perovskite compounds,[(N-CH3)4-2-methylpi]BiX5(X=C1?Br?I)(1?2?3)?[2,2-Bipy]BiX4(X=C1?Br?I)(4?5?6),were synthesized by solvothermal methods.The crystal structures?uv-vis diffuse spectrum and conductive properties were measured.Results reveal that absorption spectra will shift to red and band gap narrow down from Cl to I.The formation of different quantum well structure by using different amines will further change its optical and conductive properties.2.We have synthesized a compound[(cyhexyl)NH3]3Bi2I9(7)with a reversible phase transition by choosing cyhexylamine.Further,based on mixed-amines strategy,we have introduecd dimethylamine to benzylamine and successfully synthesized a double amines perovskite compound[(CH3)2NH2(ph-CH2NH2)2]BiBr6(8).The ferroelectric properties of 8 were charactereized by dielectric,variable-temperature nonlinear optical and ferroelectric tests.At 340 K,the coercive field is about 20 kV/cm with a remnant polarization of 1.0 uC·cm-2.Further PFM testing showed that the existence of ferroelectric domains and reversal ferroelectric domains.3.We successfully synthesized two core-shell heterostructures,[NH2(CH3)2][Mn(HCOO)3]@[NH2(CH3)2][Co(HCOO)3](9)[NH2(CH3)2][Mn(HCOO)3]@[NH2(CH3)2][Ni(HCOO)3](10)via expitaxial growth method,and realized the multi-step phase transition of complex perovskite.The phase transition processes were determinated by DSC.Epitaxial growth method not only can realize the composition of materials,but also can concentrate anvantages of multi-components.This method makes it possible to assemble multifunctional materials.