The Dielectric Phase Transition Of Cyclic Organic Components Based Hybrid Perovskites

Phase transition materials are a type of multifunctional materials,which are highly sensitive to external stimuli.In particular,the organic-inorganic hybrid compounds with reversible dielectric phase transition are very attractive materials that are widely used in data storage,data communication and signal sensing.At present,the phase transition points of most switchable dielectric materials are below room temperature,which limits their wide applications.Therefore,it is urgent to explore high-temperature dielectric phase transition materials.Organic-inorganic hybrid lead halide perovskites(LHPs)materials are a new class of molecular materials that feature excellent characteristics of both organic and inorganic materials,and exhibit many extraodinary physical and chemical properties.Compared to three-dimensional(3D)hybrid perovskites,low-dimensional perovskites show greater structural flexibility and adjustability of photoelectric properties,which provides the possibility of exploring new attractive solid phase transition materials.In this research,we have constructed new phase transition materials by introducing cyclic organic compounds with flexible structures into the organic-inorganic LHP framework.Using piperidine as the organic component,three low-dimensional LHPs with chlorine,bromine and iodine halogen ions have been prepared by the anti-solvent vapor-assisted crystallization method.The three compounds were characterized with differential scanning calorimetry(DSC),differential thermal analysis(DTA)and variable temperature powder X-ray diffraction(VT-PXRD)techniques.Compound[C5H12N]2PbCl4(1)was found to undergo an above-room-temperature reversible phase transition at Tc(?)352 K.Through X-ray single crystal diffraction,we found that the organic moiety of Compound 1 underwent an order-disorder conversion,and the inorganic framework experienced a pentahedral to octahedral transformation.The analysis of the dielectric test results shows that Compound 1 undergoes a dielectric phase transition at Tc(?)352 K,and a reversible switch between high and low dielectric states.The high dielectric constant is more than twice of the low dielectric constant.On this basis,we have expanded the structure of this type of dielectric phase transition organic-inorganic LHPs materials.Four new low-dimensional LHPs materials have been synthesized by introducing pyridine and aziridine as the organic components.Single crystal structures of these four compounds were obtained by X-ray single crystal diffraction structural analysis,and the spectral characteristics were studied by ultraviolet-visible diffuse reflectance spectrum.They were found to be semiconductor materials with direct band gaps.Their dielectric phase transition properties are under further study.The research on dielectric phase transition hybrid organic-inorganic lead halide perovskite materials in this paper provides guidelines for future design and synthesis of new high-temperature responsive dielectric switchable materials,and meanwhile contributes to the potential application of low-dimensional LHPs materials.