The Dielectric Properties Of Zero-dimensional And One-Dimensional Compounds Containing Trimethyl Phosphine

Phase transition materials have recently attracted great attention owing to their wide applications in the fields of data communication,signal processing,storage,environmental monitoring,etc.Phase transitions are always accompanied by anomalies of physical properties,such as electrical and optical properties as responses to external stimuli.In order to investigate new phase transition materials,we have synthesized a series of new compounds based on the trimethylphosphonium derivative,and research their crystal structures and dielectric properties.This thesis contains 11 structures:[(CH3)3PCH2OH][C6H3N3O7](1),[(CH3)3PCH2Cl]2[ZnCl4](2),[(CH3)3PCH2Cl]2[ZnBr4](3),[(CH3)3PCH2Cl]2[CoCl4](4),[(CH3)3P(CH2)2Cl]2[CdBr4](5),[(CH3)3P(CH2)2Cl]3[Sb2Br9](6),[(CH3)3P(CH2)2C1]2[CoCl4](7),[(CH3)3PCH2OH][Cd(SCN)3](8),[(CH3)3PCH2Cl][Cd(SCN)3](9),[(CH3)3P(CH2)2OH][Cd(SCN)3](10),[(CH3)3PCH2OH][CdBr3](11).The phase transition compounds have studied by the single crystal structure and dielectric analysis,and the DSC measurements were carried out to determine whether the compound has a reversible phase transition.The DSC measurements for 8 were carried out.There is a pair of heat anomalies on heating and cooling,indicating that 8 exhibits a reversible structural phase transition.The broad shape of heat anomalies and the narrow thermal hysteresis reveal its second-order phase transition features.After that,the dielectric properties of 8 have been studied.The dielectric anomaly near 240 K is found,which is in accordance with the results of DSC.The typical dielectric relaxation of 8 was found.The structural phase transition of 8 is due to the deformation of zigzag chains and the disorder-order transition of the cations.The switching from SHG-off to SHG-on states corresponds well to the symmetry breaking from centrosymmetric to non-centrosymmetric structures.Compound 11 have one heat anomaly in the DSC measurement process.However,there are two thermal anomalies in the cooling process.In spite of this,the heat value in the heating and cooling process is approximately equal.The crystal structure of 11 was also measured.The phase transition may be ascribed to the motion or rotation of the cations and the displacement of atoms upon heating.There is a dielectric anomaly in heating process.There are two dielectric anomalies in cooling process.Other compounds have no dielectric anomalies in both heating and cooling processes,and determined no structural phase transition.