由於微波介電共振器具有適當的介電係數、低的共振頻率溫度係數和低介電損失，使得微波介電共振器被廣泛的應用在微波通訊元件上。本實驗探討摻雜2wt%、4wt%、6wt%和8wt% MgO-CaO-SiO2-Al2O3 (MCAS) 玻璃之 (1-x)Al2O3 - xTiO2 (x=0.08, 0.12, 0.16)介電共振器陶瓷材料的晶相和微波介電特性。由於Al2O3之共振頻率溫度係數為負(τf = -55 ppm/℃)而TiO2之共振頻率溫度係數為正(τf = +450 ppm/℃)，所以希望以混合粉末的方式來製作τf ~0 ppm/℃之陶瓷。另外，本研究亦以不同MCAS玻璃含量液相燒結促進劑，探討其降低燒結溫度之效果。
在摻雜MCAS之 (1-x)Al2O3 - xTiO2 系統中，Al2TiO5 相大約出現在1250℃，在TiO2相耗盡前Al2TiO5相強度隨燒結溫度和MCAS玻璃增加而增加。隨著燒結溫度增加，在1250℃時介電係數和Q×f 值到達最大值，而τf 值可由正轉換到負。在摻雜2wt% MCAS之 88mol%Al2O3 - 12mol%TiO2 組成中，燒結溫度在1300℃時能得到最佳的τf 值(–0.6 ppm/℃)。MCAS的含量、TiO2的含量和燒結溫度的改變，會得到不同微波介電特性的陶瓷材料。 在摻雜MCAS玻璃之(1-x)Al2O3 - xTiO2 系統中，可得到εr=7~9.5、Q×f=6500~1100和τf= -60 到 +40ppm/℃等不同的微波介電特性。因此我們可藉由調變不同的MCAS含量、TiO2含量和燒結溫度來得到最佳特性的微波介電陶瓷材料。

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 (τf = -55 ppm/℃) and the material TiO2 with positive τf value (τf = +450 ppm/℃), it is desired to produce the ceramics with τf ~0 ppm/℃. 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℃, 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×f values can be obtained at 1250℃, and the τf values shift from positive to negative. The optimum τf value of –0.6 ppm/℃ exists in the 88mol%Al2O3 - 12mol%TiO2 composition with 2wt% MCAS addition and sintering temperature of 1300℃. 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： εr=7~9.5, Q×f=6500~11000, and τf = -60 to +40ppm/℃. 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.

Contents
Page
Chapter 1 Introduction………………………………………………………………....1
Chapter 2 Theory……………………………………………………………….……...4
2-1 Theory of liquid phase sintering…………………………………….……….4
2-2 Theory of microwave dielectric properties…………………………….….…6
2-3 Theory and analysis of dielectric resonator…………………………..……...9
Chapter 3 Experimental procedures..…………………………………….………..…12
3-1 Sample preparation……………………………………………………...….12
3-2 Measurement method of microwave dielectric properties…...……………..13
(Ⅰ) Calculation of dielectric constant……………………………………...13
(Ⅱ) Measurement of Q values……………………………………………14
(Ⅲ) Measurement ofτf values…………………………………………16
Chapter 4 Results and discussion……………………………………………….……18
4-1 X-Ray diffraction (XRD) analysis……………………………………..…...18
4-2 SEM analysis………………………………………………………………..19
4-3 Analysis of density………………………………………………………….20
4-4 Analysis of microwave dielectric properties………………………………..21
(Ⅰ) Dielectric constant (εr)………………………………………………..21
(Ⅱ) Q×f values…………………………………………………………….23
(Ⅲ) Temperature coefficient of resonant frequency (τf)………………...24
Chapter 5 Conclusion.……………………………………………………………..…27
References………………………………………………………………………..…29

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