| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 101 === The random-field and the generation of polar nano regions (PNRs) are considered as the main effect of the weird relaxors properties. However, there is still no conclusion about their generation mechanism. In order to investigate the random-field effect on domain morphology and dielectric properties in normal ferroelectrics and relaxors, we adopted Ab initio and Monte Carlo simulation, respectively. We calculated the domain wall energy barriers of Pb0.5Zr0.5TiO3 and Sr0.5Ba0.5Nb2O6 by Ab initio and Nudged Elastic Band. However, the actual atom diffusion path is not a linear path that we set, so the result was not accepted. On Monte Carlo part, we use Ising model to research the domain morphology and dielectric properties under different a.c. field for both materials and attempt to establish the corelation between domain morphology and dielectric properties. The susceptibility of the materials is positive correlated to their polarization ability. The easier the material polarized, the higher the susceptibility. For normal ferroelectric and relaxors, the lattice polarization contributes the highest proportion to their total polarizations. Thus under a.c. field, the susceptibility would rise as the flipping dipoles increase in the field cycle. The simulation results show that the quantities of flipping dipoles would be greater under higher temperature、stronger field amplitude or lower field frequency conditions so that the susceptibility would also be higher. Due to the random-field effect in relaxors, they possess more flipping dipoles under lower temperature conditions, so the susceptibility of relaxors is higher than normal ferroelectrics and Tm (the temperature where the peak of real part susceptibility tale place) is lower than normal ferroelectrics.
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