Exploration On The Dielectric Properties Of Nitrogen Containing Heterocyclic Compounds

Phase transition materials, especially ferroelectrics materials, have currently being investigated as potential materials for many micro-device applications such as DRAM, Fe TRAM, infrared detectors, piezoelectric transducers, nonlinear optical devices, etc. So far, more than three hundred ferroelectrics have been reported, but just a few of them can be used to produce devices. To found appropriate phase transition materials for practical use, scientists have synthesized a series of compounds based on the heterocycles containing nitrogen and determined the structures by X-ray diffractometer. They also discuss the dielectric properties of these compounds in order to explore the phase transition rules.This thesis consists of 11 crystalline structures, (C4H5N2)+·PF6- (1), (C4H5N2)·Br-(2), (C4H5ClN3)+·NO3- (3), (C4H5N2)+·CdCl3-(4), (C4H5N2)22-·CdBr42-(5),(C4H5N2)2-·CdI42-(6), C12H24O6·C4H5N2+·ClO4-(7), C12H24O6·C4H5N2+·BF4-(8), C12H24O6·C4H5N2+·PF6-(9), (10), C12H24O6·C5H7N2+·I- (11). We respectively measured the infrared (IR), powder diffiction (PXRD), crystal structure and the dielectric properties of these eleven substances. We analyzed the potential possibility of the phase transition by observing the curves of dielectric constant versus temperature. We found that 1 and 2 undergo the reversible phase transitions. At low temperature, DSC measurement of 1 shows a couple of peaks in the heating and cooling runs. Moreover, its variable-temperature structure determination discloses that the order-disorder transformation of negative ions contribute to the occurrence of the phase transitions. The unusual dielectric peaks of 2 appear at 357.5 and 365 K respectively. The structural analysis displays the order-disorder transition of the pyridazine ion gives rise to the phase transitions. The other compounds show no dielectric anomalies during heating and cooling processes.