Design And Phase Transition Properties Of Nitrate-linked Organic-inorganic Hybrid Perovskite Materials

Solid-state structural phase transition materials as an important branch of responsive materials with special structures can respond to external stimuli,resulting in the reversible structural changes and property switchings.Intriguing properties,such as phase transition,dielectric transition,ferroelectric,ferroelastic,photoluminescence,etc.In this context,molecule-based organic-inorganic hybrid perovskite materials with dielectric switching have attracted much attention.However,most of the hybrid materials are based on halogen as a bridging ligand.Accordingly,polyatomic ligand bridged hybrid materials are highly desirable.Because they have abundant coordination geometry,deformable flexibility,relatively small steric hindrance effect,and so on.To take full use of organic ligands to achieve dielectric transitions,we chose nitrate ion as polyatomic bridged ligand to construct hybrid materials.Beside environmental friendliness,nitrate ion has advantages in construction of stimuli-responsive or smart materials.Firstly,nitrate ion is multiple-atom ligands covering a wider range of chemical and physical properties,so it can interact with metal with various fashions.Secondly,the radius of nitrate ion is equivalent to that of iodine ion,which allows it to be connected to heavy atoms.Thirdly,as is known,nitrate ion exhibits diverse coordination modes,such asμ₂-κ²（O,O?）,μ₂-κ³（O,O?）,μ₂-κ³（O,O?,O??）,μ₂-κ⁴（O,O?,O??）,μ₂-κ⁴（O,O?）,and so on.Based on the mentioned advantages,this thesis carries out the following two parts of work:（1）A series of nitrate-linked organic-inorganic hybrid double perovskite-type compounds with switchable dielectric constant were synthesized:（Q）₂[（NH₄）Bi（NO₃）₆]（1）、（Q）₂[KBi（NO₃）₆]（2）、（Q）₂[Rb Bi（NO₃）₆]（3）、（Q）₂[Cs Bi（NO₃）₆]（4）were obtained.Crystal structural analysis and dielectric constant measurements reveal the order-disorder transition of the cation guest and the distortion of the anionic cage-like host,are the origin of the phase transitions.This arouses switchable dielectric constant between high-and low-dielectric state,making them a type of switchable dielectric materials.Furthermore,the phase transition temperature of compound 2 to 4and the radius of the alkali metal ion has a linear relationship in a wide temperature range.（2）A series of alkali metal nitrate-linked organic-inorganic hybrid perovskite-type compounds with high phase transition temperature were obtained.Respectively,（Piperazine）K（NO₃）₃（5）、（Piperazine）Rb（NO₃）₃（6）、（Homopiperazine）K（NO₃）₃（7）、（Homopiperazine）Rb（NO₃）₃（8）、（1-Methylpiperazine）K（NO₃）₃（9）、（1-Methylpiperazine）Rb（NO₃）₃（10）.The phase transition temperature of compounds 5 to 8 decreases with the increase of the radius of the coordinated alkali metal ion.However,the change of compound 9 and 10 is on the contrary,which is reflected in that the phase transition temperature of compound 10 is about 30 K higher than that of compound 9.Crystal structure reveals that it is related to the transformation of coordination pattern between nitrate ions and alkali metal ions in inorganic skeleton.In summary,a series of nitrate-linked organic-inorganic hybrid perovskite-type compounds were synthesized.Considering structural diversity and rich physical properties,the nitrate-linked hybrid organic-inorganic perovskite-type compounds would find roles in the exploration of promising organic-inorganic hybrid electronic materials.