Microwave dielectric resonators (DRs) are being widely used in microwave telecommunication devices owing to their excellent characteristics of suitable dielectric constant, good temperature stability, and low dielectric loss. In this study, the crystalline phase and the microwave dielectric properties of the (1-x)Al2O3 - xTiO2 (x=0.08, 0.12, 0.16) compositions with 2wt%, 4wt%, 6wt%, and 8wt% MgO-CaO-Al2O3-SiO2 (MCAS) glass addition have been investigated. By combining the material Al2O3 with negative temperature coefficient of the resonant frequency (£nf = -55 ppm/¢J) and the material TiO2 with positive £nf value (£nf = +450 ppm/¢J), it is desired to produce the ceramics with £nf ~0 ppm/¢J. The MCAS is used as liquid-phase sintering aid to lower down the sintering temperature. In the MCAS-doped (1-x)Al2O3 - xTiO2 system, the Al2TiO5 phase starts to appear at about 1250¢J, and then the crystalline intensity of Al2TiO5 phase increases with the increase of sintering temperatures and MCAS glass content, until the temperatures that TiO2 is consumed. As the sintering temperature increases, the maximum dielectric constants and Q¡Ñf values can be obtained at 1250¢J, and the £nf values shift from positive to negative. The optimum £nf value of ¡V0.6 ppm/¢J exists in the 88mol%Al2O3 - 12mol%TiO2 composition with 2wt% MCAS addition and sintering temperature of 1300¢J. The MCAS content, TiO2 content, and sintering temperature will result in the variation of microwave dielectric properties. In this study, MCAS-doped (1-x)Al2O3 - xTiO2 system exhibits the microwave dielectric properties of¡G £`r=7~9.5, Q¡Ñf=6500~11000, and £nf = -60 to +40ppm/¢J. By adjusting the MCAS content, TiO2 content, and sintering temperatures, ceramics with good microwave properties can be obtained in the MCAS-doped (1-x)Al2O3 - xTiO2 system.

Thin film coatings of (Cao.6Mg0.4)Zr4(P04)6 (CMZP) and Mg stabilized AhTiOs ( Mg-Ah Ti05 ) on dense SiC substrates were investigated using sol-gel coating techniques. The thickness and quality of both CMZP and Mg-Ah Ti05 coatings were found to depend on the solution concentration and lift rate. Double coatings were applied to obtain homogeneous and crack-free coatings. The quality of double coatings was influenced by different first and second coating thickness. The CMZP coated samples were fired in controlled atmospheres to have the pure CMZP phase. Unhydrolyzed solution of Mg-AhTiOs was utilized instead of hydrolyzed solution to improve the quality of Mg-AhTiOs coatings. Aging process was found to improve the quality of CMZP and Mg-Ah TiOs coatings. SiC samples coated with CMZP and Mg-Ah TiOs exhibited good thermal shock resistance and greatly improved the high temperature alkali corrosion resistance. / Master of Science