| Summary: | 博士 === 國立臺灣大學 === 物理學研究所 === 107 === High dielectric constant and low dielectric loss are of great importance for the energy saving and efficient power delivery. This thesis aims to investigate fundamental frequency dependent dielectric properties and high-k dielectric constant in the double perovskites related oxides. Throughout this thesis, we have observed the role of the oxygen stoichiometry and polarization on the dielectric properties of the double perovskites oxides, allowing a great understanding of the synthesis condition and polarization mechanisms.
In the first section of the thesis, we explore the dielectric properties of the double perovskites Ba2LnRuO6 samples sintered at different cooling rates, using the impedance techniques in order to resolve the electrical heterogeneities components contributing to the dielectric constant. We observe a significant polarization dependence on the microstructure due to the grain/grain boundary effect at high and low temperatures..
The second section of this thesis investigates the dielectric materials Ba2LnMoO6 sintered at different atmospheres, one is in the Ar/H2 and the other is in the O2. We observe that Ba2LnMoO6 sintered in Ar/H2 shows a high dielectric constant while the Ba2LnMoO6 sintered in O2 exhibits a low dielectric constant. This allow us to tune the oxygen stoichiometry and obtain the more intrinsic dielectric properties for Ba2LnMoO6.
The final part of the thesis is to investigate 2- and 4- terminal spin transfer torque systems using non-equilibrium Green function method. For coherent cases, We find that the lateral geometry (4-terminal) renders enhanced anti-damping torques compared with the conventional one (2-terminal) in a certain parameter region. For incoherent cases, we discover that the dephasing can enhance the anti-damping torque. The results show that enhancement of the anti-damping torques declines when the scattering region is longer. For the four-terminal MTJ of larger scattering length, the dephasing can expedite the anti-damping torque.
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