| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 91 === Abstract
In this research, two kinds of material for components of high frequency communication have been synthesized and evaluated.
[a]Low dielectric constant materials
To develop a low-loss, lead-free, non-alkali, low cost substrate material for microwave/microelectronics applications, composites in the (SrxBa1-x)O-Al2O3-2SiO2-yB2O3 system (x in molar ratio while y in wt%) were explored. The solid-state reaction route was successfully used to prepare the ceramics. Thermal characteristics, microstructure, phase transformation and dielectric properties were studied with the addition of SrO and B2O3. An appropriate addition of SrO helps to enhance the transformation from hexacelsian to celsian, and besides effectively reduces thermal expansion coefficient of the ceramics. The addition of B2O3 was successful to increase sinterability.The (Sr0.375Ba0.625)O-Al2O3-2SiO2 ceramic has the lowest average thermal expansion coefficient (5.718×10-6/℃) and the highest degree of transition (46.7%) from hexacelsian to monocelsian. The (Sr0Ba1)O-Al2O3-2SiO2- 2wt% B2O3 ceramic possesses dielectric constant of 6.028, and Q×f of 6700 GHz which is higher than the value reported in literature.
[b]Ferrimagnetic material
The purpose of this work was to obtain yttrium iron garnet powder by microwave-induced combustion method. The powder was obtained from nitrate salt solution by controlling the amounts of urea (fuel). This study showed that the controlled amounts of urea have a great effect on particle size. The combustion synthesis of stoichiometric urea (YIG-1) resulted in amorphous powder with high surface area (16.63 m2/g). The triple urea (YIG-3) batches resulted in crystalline powder with low surface area (1.64 m2/g). Sintering at 1425℃-6hr, YIG-1 ceramics have larger theoretical density (99.90%) than those of solid-state-reacted powder (98.65%). Remanent magnetization (Br) and coercive force (Hc) decreases with sintering temperature, basically due to the increases in sintered density for the materials. The combustion method leading to powders with decreased calcining temperature and lower the sintering temperature necessary for densifying the materials proves to be a versatile means.
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