| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 95 === Microwave dielectric resonators which are fabricated by high dielectric constant, low dielectric loss and good temperatur stability of microwave dielectric materials are suitably applied in microwave filters, oscillators and antennas. With the recent progress of microwave communication devices, miniaturization of microwave components for volume efficiency is a major research requirement. To develop microwave dielectric materials, lower sintering temperatures plays an important role in the future. As mentioned above, the main research of this dissertation is divided two parts which preparation of low sintering temperature microwave dielectric resonators and development of new dielectric material systems.
The effect of CuO and B2O3 additions to AB2O6 (A=Mg and Zn, B=Nb and Ta) were investigated. Not only reduce the sintering temperature effectively but improve the dielectric loss. For 0.5 wt% addition to the MgTa2O6 ceramics sintered at 1400oC, the dielectric properties gave: εr ~28, Q×f ~58000 (GHz), τf ~18ppm/oC. With 0.5 wt% addition of CuO sintered at 1230oC, dielectric properties of ZnTa2O6 ceramic showed:εr ~34.6, Q×f ~65000(GHz), τf ~5ppm/oC. Beside, with 1 wt% CuO-doped sintered 1290oC, the 0ppm/oC value of τf could be achieved. With 0.25 wt% B2O3 addition, a dielectric constant of 21.5, a Q ×f value of 118000(GHz) and a τf value of –48ppm/oC of MgNb2O6 ceramics doped with B2O3 sintered at 1260oC for 3 h are obtained.
The typical dielectric performances of MgTiO3, MgTa2O6, Ca0.6La0.8/3TiO3 and Ca0.6Nd0.8/3TiO3 ceramics were investigated. The new dielectric material system could be obtained by mixing two materials mentioned above. 0.7MgTiO3-0.3MgTa2O6 ceramic sintered at 1460oC possesses the excellent microwave dielectric properties of εr ~ 23, Q ×f value ~ 81000(GHz) andτf value ~ -2ppm/oC. A dielectric constant of 27, a Q ×f value of 134000 (GHz) and aτf value of 7.46 ppm/oC were obtained for 0.8MgTiO3-0.2Ca0.6La0.8/3TiO3 ceramics. For xMgTiO3-(1-x)Ca0.6Nd0.8/3TiO3 ceramics, the εr value varied from 20 ~ 34, the maximum Q × f value was obtained at 1390oC when x=0.9, the τf value varied from 35 ~ -10ppm/oC. The existence of MgTi2O5 phase would cause a decrease in the Q × f value. The density as well as the the Q × f values increased with the increasing of the sintering temperature and the degradation was observed owing to the abnormal grain growth.
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