| Summary: | 碩士 === 中國文化大學 === 化學工程與材料工程學系奈米材料碩士班 === 100 === In order to reduce the cost of sintered AlN ceramics, the need to develop low-temperature sintering of AlN ceramics process has caught our attention, as a motivation for this study. Two kinds of liquid-phase sintering additives, La2O3 and Y2O3, were chosen to achieve the low-temperature sintering process. The relative sintered density and shrinkage of AlN ceramics at sintering temperatures of 1300 ℃, 1400 ℃, and 1500 ℃ respectively were carefully estimated. The composition and microstructure of the second phase produced during sintering process were investigated, as well as the effect of second phases on the dielectric properties of AlN ceramics were intensively analyzed.It was found in this study that the higher sintering temperature, the longer sinterng time, and sintering additives contributed to enhance the density of AlN ceramics. However, the oxide sintering additives, which induced liquid-phase sintering and produced the second phase in consequence, and the growth of grain size caused the increase of oxygen impurity and dielectric loss ε”. We have learned from the Nyquist plots by using 4294A impedance analyzer to measure the AlN ceramics, the electronic conductivity of AlN ceramics is by the path of grain boundaries, rather than the grain. From Colt-Colt plot analysis, it was observed that the dielectric constant ε’ decreases as the frequency increases. The polarization mechanism of AlN ceramics was found to be space charge polarization in the range 1-104Hz. When compare the dielectric properties of add La2O3, or Y2O3 as sintering additives to pure AlN ceramic, the dielectric constant obtained in the frequency of 1MHz ε' were between 6 and 7 for same sintering process. However the larger grain size leads to the increase of loss tangent (tanδ), dielectric loss ε”, and dielectric constant ε’.
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