Design And Phase Transition Properties Of Organic-Inorganic Hybrid Perovskite Materials Based On Alkaline Earth Metal

Reversible phase change materials undergo corresponding changes in their crystal structure,accompanied by changes in properties to respond external stimuli.For dielectric materials with temperature-stimulated response,the dielectric constant can be switched between high and low dielectric states under temperature stimulation,enabling applications in information storage.However,the halogen radius of organic-inorganic hybrid halogen perovskite,which is the most widely studied in dielectric properties,limits the selection of organic cations.Therefore,the limitation of tolerance factor can be reduced by replacing halogen anions with polyatomic bridging ligands.Based on this,we selected perchloric acid and tetrafluoroboric acid as polyatomic bridging ligands to construct a series of ABX₃ hybrid perovskite compounds.This thesis carries out the following three parts of work:（1）Two ABX₃ compounds（C₃H₅N₂）Ba（Cl O₄）₃（compound 1）and（C₃H₅N₂）Sr（Cl O₄）₃（compound 2）were obtained by the reaction of protonated imidazole with strontium perchlorate and barium perchlorate.The study of thermodynamics shows that both compound 1 and compound 2have reversible structural phase transition accompanied by obvious dielectric anomalies in the 110-300 K range.Through the analysis of single crystal structure at variable temperature,the phase transition originates from the order-disorder change of imidazole cations and the relative torsion of anion skeleton.（2）Two ABX₃ were synthesized by the reaction of protonated thiazole with barium perchlorate and barium tetrafluoroborate.They are（C₃H₄SN）Ba（Cl O₄）₃（compound 3）and（C₃H₄SN）Ba（BF₄）₃（compound 4）.Also other compounds（C₄H₅N₂）₄Ba（Cl O₄）₆（compound 5）and（C₄H₅N₂）Ba（BF₄）₃（compound 6）were obtained when thiazole is replaced by pyrimidine.Thermodynamic studies have shown that compound 3 and compound 4 undergo two continuous phase transitions in the 140-300K range accompanied by dielectric anomalies.Through the analysis of single crystal structure with variable temperature,the phase transition originates from the order-disorder change of thiazole cations and the relative torsion of anionic skeleton.However,5 and compound 6 not occurred structural phase transition.（3）ABX₃ compound（C₂N₂H₇）Ba（Cl O₄）₃（compound 7）,A₂BX₄ compound(C₆NH₁₃)₂Ba（Cl O₄）₄（compound 8）and A₃BX₅(C₈H₁₄ONF)₃Ba（Cl O₄）₅（compound 9）were obtained by the reaction of protonated acetamidine,cycloexanediamine and fluoromethyl-3-hydroxyquinine with barium perchlorate.Crystal structural analysis and dielectric constant measurements reveal that the structural phase transition is caused by the order-disorder change of organic amine cations and the relative torsion of anion skeleton.Compound 7 underwent a reversible phase transition at 105 K and compound 8 underwent a reversible phase transition at 350 K.But no structural phase transition occurred in compound 9.In summary,the structure and dielectric properties of organic-inorganic hybrid perovskite can be effectively regulated by adjusting the size of amine ion at position A,metal ion at position B,and ligand anion at position X in ABX₃.