The Phase Transitions And Dielectric Properties Of Organicinorganic Hybrid Crystals Containing Thiomorpholine Or 4-piperidinopiperidine

The physical properties of crystalline material with phase transition can be transformed between two or more phases by external stimuli such as light,temperature,and electric.The solid-solid phase transition functional material constructed by this method has attracted great attention in the fields of photonic devices,optoelectronics,digital processing and sensors in recent years.The dielectric and thermal anomalies near the phase change temperature can be detected by dielectric test and DSC（Differential Scann Calorimetry）,so as to find the phase transition material effectively.Inorganic material has good electrical mobility,band gap adjustability,mechanical stability,thermal stability,magnetic or dielectric transition,making it possible to design for metal,semiconductor and insulator.The structural diversity and easy processing of organic compounds enhance the plasticity of the material.Organic-inorganic hybrid material combine the advantages of the two,which provides more possibilities for the development of phase transition material.In this paper,we adjusted the inorganic framework to optimize the performance.The thiomorpholineoline and 4-piperidinopiperidine were selected as the research objects.The phase-transition material with dielectric switching was filtrated.The relationship between the structure of the material and the properties were in-depth discussed to promote the development of controllable synthesis and application of phase transition functional material.The main work is as follows:At the first part,（thiomorpholinium）Cd Cl₃（1）with one-dimensional chain structure and（thiomorpholinium）₃Bi Cl₆（2）and（thiomorpholinium）₂Sb₂Br₈（3）with zero-dimensional structure were obtained by embedding thiomorpholine cations between different inorganic frameworks.The DSC measurement and dielectric measurement of compound 1 confirmed that compound 1underwent isomorphic phase transition at about 384.3 K accompanied by the occurrence of dielectric anomalies.The crystal 1 at variable temperature indicated that the change of cationic configuration of thiomorpholine was the main reason for the phase transition.The compound 2,（thiomorpholinium）₃Bi Cl₆ exhibits sequential thermal anomaly around 413.1 K and423.0 K.And the temperature of phase transitions is higher than room temperature.From 298 K to 453 K,the thiomorpholineine cations change from an ordered state to a disordered state.The S atoms changed from ordered state to partial splitting state and finally existed in the form of total splitting.The results of single crystal diffraction show that the gradual change of thiomorpholine cation promotes the phase transition.The discovery of the dielectric abnormality makes it possible to be applied practical.Notably,the compound 3 also shows zero dimensional accumulation.But no reversible dielectric abnormality was observed during the electrical property measurement indicating that no phase transition occured.At the second part,by the replacement of halogen anion,three new multifunctional organic-inorganic hybrid perovskite（thiomorpholinium）Pb Cl₃（4）、（thiomorpholinium）Pb Br₃（5）、（thiomorpholinium）Pb I₃（6）were successfully synthesized and underwent reversible structural transformation above room temperature,accompanied by the anomalous change of dielectric constant.With the adjustment of the halogen anion from Cl to I in the inorganic skeleton,the space group is transformed from center space group P2₁/c（（thiomorpholine）Pb Cl₃）to chiral one P2₁2₁2₁（（thiomorpholine）Pb Br₃,（thiomorpholine）Pb I₃）at room temperature.The ordered-disordered transition of organic cations and the change of hydrogen bonds with the increase of temperature lead to above-room-temperature phase transitions.Ultraviolet absorption and second-harmonic generation（SHG）measurements confirmed that both the band gap and SHG activity of（thiomorpholine）Pb X₃（X=Cl,Br,I）crystals were tunable.The band gaps reveal a broadening trend with 3.532 e V,3.410 e V and 3.175e V along the Cl→Br→I series.This work provides an effective molecular design for multifunctional organic-inorganic perovskites.At the third part,in addition to thiomorpholine,another widely used six-membered heterocyclic organic cation,piperidine,has attracted our attention.Using the 4-piperidinopiperidine as the organic part,different inorganic skeletons were selected.Successfully,(C₁₀H₂₂N₂)Sb Cl₅（7）,(C₁₀H₂₂N₂)₂[Mn（SCN）₆]（8）,(C₁₀H₂₂N₂)Zn Cl₄（9）were synthesized.Dielectric measurements were performed on the compounds in the temperature range from 153 K to 453 K.No dielectric anomalies and phase transition were found in this temperature range.