Dielectric Switch And Ferroic Phase Transition Of Organic-metal Halide Perovskite Crystals

Crystalline materials according to the crystallographic symmetry could show dielectric,piezoelectric,ferroelastic and ferroelectric properties.Driven by structural phase transition,they also can exhibit bistable switching characteristics in response to external stimuli,having widespread applications in energy conversion,data storage,intelligent control,and information sensing.With their development,various structural types of dielectric switch and ferroic phase transition crystals have emerged,including inorganic perovskites,organic compounds,organic-inorganic hybrids,polymers and so on.Among them,organic-metal halide perovskites can integrate and exert the respective advantages of organic and inorganic components at the molecular level,in which the dynamic orientation states of organic cations that sensitive to temperature can easily induce structural phase transition and the special octahedral framework of metal halides can also bring more possibilities for the diversity of physical properties.Additionally,their rich chemical diversity and high structural tunability provide a broad platform for designing switchable dielectrics,ferroelastic and ferroelectric materials,showing huge research space and promising application prospects.For dielectric switch and ferroic phase transition materials,the studies on organic-metal halide perovskite structures can contribute to deeply understand structural phase transition mechanisms,and enrich families of high-performance materials,as well as innovate technical methods for design synthesis and performance optimization.These have important scientific significance for promoting the development of molecular-based phase transition crystals.In this dissertation,based on the single crystal or thin film forms of organic-metal halide perovskites,several dielectric switching and ferroic phase transition materials were successfully designed,and their structural phase transitions,physical properties and feasibility of designed synthesis methods were systematically studied,through crystallography engineering and molecular modifications with the crystallographic symmetry as a clue.1)The differential effects of different inorganic components on the structure and properties of hybrid perovskites were investigated.(NNDP)Cd Cl3(NNDP = N,Ndimethylpiperidinium)adopts a one-dimensional hexagonal hybrid perovskite structure,while(NNDP)3Bi2Cl9 has a zero-dimensional hybrid perovskite structure.The(NNDP)Mn Cl4 and(NNDP)Mn Br4 behave as zero-dimensional stacking structure.They all exhibit remarkable dielectric switching properties,but the different structural stacking types also cause great differences in structural phase transitions,dielectric switching and other physical properties.2)A mechanochemical solid-state synthesis method was applied to realize the integration and rapid regulation of dielectric switching and luminescence properties.External mechanical stimulations enable the formation of a series of two-dimensional hybrid perovskites(cyclopropylammonium)2Pb1-x Mnx Br4(x = 0~1),with multiple tunable high-efficiency photoluminescence responses,and achieved a large enhance of 99 K in dielectric switching temperature.This saves the time-consuming and laborious crystal cultivation steps to a certain extent,and provides a new perspective for the high-efficiency synthesis and performance regulation of multifunctional phase transition materials.3)Based on the order-disorder transition mechanism,a zero-dimensional hybrid perovskite ferroelastic(N,N-dimethyl-tertbutylaminium)3Bi2Br9 was successfully designed through the group modification strategies on organic cations,which shows a high temperature ferroelastic phase transition(6/mmm Fmmm,Curie temperature Tc = 425 K)and dual dielectric switching characteristics.Systematic structural analysis reveals that the modulation of subtle intermolecular interactions plays a crucial role in regulating crystal symmetry and inducing specific dielectric switching properties4)In the periodic table of elements,nitrogen and phosphorus elements in the same main group have similar covalent properties but differ in atomic radius,mass and electronic structure.Taking(EATMA)Pb Br4(EATMA =(2-aminoethyl)-trimethylaminium)as parent,by replacing(EATMA)2+ cations with heavier and larger(EATMP)2+(EATMP =(2-aminoethyl)-trimethylphosphinium)cations,a two-dimensional hybrid perovskite ferroelectric(EATMP)Pb Br4 was successfully synthesized,with a Curie temperature(Tc)as high as 534 K.To the best of our knowledge,such a Tc of 534 K is the highest among reported two-dimensional hybrid perovskite ferroelectrics so far.In addition,it has excellent piezoelectric properties,and relevant calculations show its large electrostrictive coefficient up to 3.96 m4 C-2,far exceeding the level of polyvinylidene difluoride(PVDF)and inorganic ones.This provides a feasible reference route for designing highperformance molecular ferroelectrics,and we look forward to the emergence of more phosphine-based or sulfur-based hybrid perovskite ferroelectrics.