Research On Ferroelectric Properties Based On Diamine Antimony Or Bismuth Halide

Molecule-based ferroelectrics have drawn much attention due to their advantages over conventional pure inorganic ferroelectrics such as easy processibility,cheapness and environmental friendliness.Herein,we studied the crystal structures,phase transitions,dielectric properties and optical properties of a series of organic-inorganic hybrid ferroelectric compounds based on taking Bi(III)or Sb(III)halides and protonated propylenediamine derivatives.These finding would expand the scope of molecular-based ferroelectric materials.The main content of the thesis includes three parts:The first part reported seven compounds,(H2mdap)[BiCl5](1),(H2mdap)[BiBr5](2),(H2mdap)[BiBr3.,Cl1.9](3),(H2mdap)[BiBr1.8Cl3.2](4),(H2mdap)[BiBr1.4Cl3.6](5),(H2mdap)[BiBr1.1Cl3.9](6)and(H2mdap)[SbCls](7)(mdap = monomethyl-propanediamine).Compound 1 exhibits a ferroelectric to paraelectric phase transition at 372 K.Compounds 2-6 undergo similar structural phase transitions as 1.The phase transition temperatures increase with the increase of Cl content,inducing large changes of dielectric and second-order nonlinear optical properties.Compound 7 showed no dielectric anormaly.The second part reported two compounds,(H2tmpda)[SbCl5](8)and(H2tmpda)[SbBr5](9)(tmpda = N,N'-tetramethyl-propanediamine).Compound 8 has no dielectric anormaly.Compound 9 showed dielectric anomaly at 360 K,but no changes observed in DSC and structures..The third part reported two compounds,(H2dmpda)[SbCl5](10)and(H2dmpda)[SbBr5](11)(dmpda = N,N'-dimethylpropanediamine).Compound 10 has no dielectric anormaly.Compound 11 exhibited dielectric anomaly at 300 K and a pair of reversible peaks in DSC,indicating teh occurrence of a structural phase transition.