| In order to reduce circuit/device size, many microwave ceramics with high dielectric constant have been studied these years. CaTiO3 ceramic was a nice material with high dielectric constant, however the sintering temperature of pure CaTiO3 was very high (≥400℃) and it has the relative low Q×f value (-3500GHz) by the traditional solid-state preparation process. Many researches have been done to solve these problems. Sol-gel method has been used for the fabrication of microwave ceramic materials with improved compositional homogeneity, lower densification temperatures, and better dielectric properties.In this thesis, sol-gel method has been used to synthesize well dispersed CaTiO3:Zn nano particles. The synthesized nano particles were then sintered to ceramics, and the effects of the added Zn to the ceramics were investigated. The mian part of the thesis are as follows:1. The sol-gel process was a complex process which was effected by many factors. So we first investigated the effects of three main factors to the sol-gel process including:concentration of precursor, H+/Ti4+value and the addition of dispersant, to find out a suitable chemical environment. Then the synthesized gel was heat-treated at 500℃and well dispersed nano-particles with diameter size about 25 nm were obtained.2. Zn was introduced into CaTiO3, the effects of the added Zn to the sintering and microwave properties were investigated.When Zn was introduced as substitution of Ca in A site, it made great role in reducing the sintering temperature of the ceramics. The XRD patterns showed that the added Zn conbined with Ti to form Zn2TiO4 or Ca2Zn44Ti15O3 which possess lower sintered temperatures and higher Q x f values than CaTiO3. So the (Ca1-χ,Znχ)TiO3 ceramics could be sintered at lower tempuratures and possessed higher Q x f values. (Ca1-χ,Znχ)TiO3 (x=0.01) ceramics sintered at 1150℃exhibited good dielectric properties with a dielectric constant of 159 and a Q x f value of 5416 GHz..While for the Ca(Zny,Tii.y)O3-8 (y=0.01) ceramics, the added Zn substituted for Ti in the B site and formed a solid solution so that had little impact to the sintering temperatures; the sintered temperature of Ca(Zny,Ti1-y)O3-8(y=0.01) was 1250℃which equals to that of CaTiO3. In samples Ca(Zny,Ti1-y)O3-8 (y=0.05) and Ca(Zny,Ti1-y)O3-8 (y=0.1), a second phase ZnO appeared and the sintered temperatures reduced to 1200℃and 1150℃respectively. Ca(ZnY,Ti1-y)03.6 (y=0.01) sintered at 1250℃obtained the dielectric properties as:ε=165, Q×f=6819GHz.For samples CaTiO3+zZn, dense ceramics were sintered at 1150℃with the main phase CaTiO3 and second phase Zn2TiO4.CaTiO.:0.05Zn ceramic sinterd at 1150℃exhibited good dielectric properties with a dielectric constant of 155 and a Q×fvalue of 6633GHzFor all the three ways, the Q x f values of the ceramics increased than CaTiO3 due to the addition of Zn. When the added Zn existed as ZnO or conbined with Ti to form Zn2TiO4 or Ca2Zn4Ti15O3 (in (Ca1-χ,Znχ)Ti03 and CaTiO3:zZn), the sintered temperatures of the ceramics would be reduced; while in the Ca(Zny,Ti1-y)O3-f (y=0.01), the added Zn substituted for Ti site and formed a solid solution so that had little impact to the sintered temperature. |
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