Design,Synthesis,Phase Transformation And Ferroelectric Properties Of Low Dimensional Cd-based And Metal-free Perovskite Materials

As an important branch of perovskite,organo-inorganic hybrid perovskite(OIHPs)has attracted extensive attention in recent years due to its diverse structure,low manufacturing cost and easy manufacturing.Although a large number of photoelectric applications have been demonstrated,the study of the basic properties of low-dimensional perovskites has not attracted much attention from researchers.After dimensionality reduction,some intrinsic properties of perovskite materials,such as band structure and photon transmission,will show different behaviors.In this paper,four hybrid perovskite compounds were synthesized based on the theoretical basis of related literatures,and dielectric testing,X-ray single crystal diffraction,differential scanning calorimetry(DSC),ultraviolet absorption,fluorescence,nonlinear optical effects(SHG)and other testing and analysis methods have been used to research their structures and properties.In this paper,two-dimensional,one-dimensional,zero and metal-free hybridized perovskites have been studied successively.The main contents are as follows:1.A 2D organic-inorganic hybrid perovskite,[C6H5(CH2)4NH3]2CdCl4(4PBA-CdCl4)(1)is synthesized through solution diffusion method and experiences two continuous phase transition,including a centrosymmetric triclinic P1 to a non-centrosymmetric polar chiral monoclinic P2 to another centrosymmetric tetragonal P4/mmm with increasing temperature,accompanied by symmetry breaking,as a result of the prominent CdCl6 octahedral distortion and disorder transformation of organic 4PBA cations.In addition,4PBA-CdCl4 possesses a wide band gap of 4.376 eV and is chiefly derived from the contribution of inorganic CdCl6 octahedron.This work provides an avenue to accelerate the search for new organic-inorganic hybrid perovskites with new phase transitions and innovative physical properties.2.By applying a strategy of regulating the stoichiometric proportion of R-MPA and CdCl2 with 1:1(2)and 2:1(3),two high-Tc low-dimensional perovskite ferroelectrics,1D(2)and 0D(3)[R-MPA]2CdCl4[R-MPA+=(R)-(-)-1-methyl-3-phenylpropylamine],are successfully synthesized.By a series of experimental characterization,we discover that 3 has emerged as a 0D chiral ferroelectric with distinct circularly dichroism and increased ferroelectricity with high Curie temperature and spontaneous polarization and corresponding large dielectric constants,SHG response,and semiconducting property as compared with 2.This finding opens up an avenue to explore new low-dimensional lead-free metal halide ferroelectric s,especially the OD chiral lead-free metal halide ferroelectric semiconductors with a high-Tc for practical applications.3.We have successfully demonstrated a metal-free molecular compound(PIPz)(NH4I3)·H2O(4;PIPz=Piperazinium)undergoes a structural phase transition from an orthogonal symmetric space group Pbcn to another orthogonal symmetric space group Pbcm at a relative low Curie temperature,as demonstrated by DSC and singlecrystal X-ray diffraction.This is attributed to the PIPz2+and H2O moiety undergoes reorientation and disorder conversion as well as the disorder of the NH~+ cation...