| According to the recent reports,(Mg0.9Zn0.1)2TiO4 ceramic has excellent microwave dielectric properties and high breakdown strength. Therefore, in this thesis(Mg0.9Zn0.1)2TiO4 ceramic was chosen as the research objects, through bring in several new elements, changing the way of sintering, the microwave dielectric properties and breakdown strength were wished to be further improved.Because of the generation of oxygen vacancy and Ti4+ ion reducing in this ceramic upon high temperature sintering process. In the third chapter of this thesis, the Mn element was introduced to the(Mg0.9Zn0.1)2TiO4 ceramic with the hoping of improving its comprehensive properties. Finally the(Mg0.9Zn0.1)2(Ti1-xMnx)O4 ceramics(where x=0.005, 0.01, 0.02, 003) were synthesized, and the XRD results showed that the ceramics have a pure phase composition structure of spinel. When the x value equals to 0.01, the(Mg0.9Zn0.1)2(Ti1-xMnx)O4 ceramics sintered at 1450 oC temperature obtained dielectric performance as follows: ?r~14.8,tan?~5.3×10–5,?f~–57.8 ppm/oC. Studying on the relationship between the thickness of the sample and its breakdown strength showed that, the breakdown strength decreased with the increase of the thickness of the ceramic sample obeying the exponential decline rule, and when the sample thickness is 0.2 mm, the breakdown strength of this ceramic achieved a value of as high as 102 k V/mm. Through the study of the impedance spectrum, we found that the schottky barrier does not exist in the grain boundaries of these ceramics.In the work of the chapter 4, Ca element was introduced to the(Mg0.9Zn0.1)2(Ti0.99Mn0.01)O4 ceramic, and we finally synthesized the(Mg0.9-yCayZn0.1)2(Ti0.99Mn0.01)O4 ceramics(where y=0.01, 0.03, 0.05, 007), so as to enhance the dielectric constant of the ceramics, and to adjust its resonant frequency temperature coefficient. XRD diffraction analysis showed that the Mg2 TiO4 and Ca TiO3 two phases coexisted in these ceramics, SEM observations showed that there were many pores inside of them. When y=0.01, the(Mg0.9-yCayZn0.1)2(Ti0.99Mn0.01)O4 ceramic sintered at 1450°C effectively improved the dielectric constant, and had a smaller resonant frequency temperature coefficient, its microwave dielectric properties are showed as follows: ?r ~15.03, Q×f~48694 GHz,?f~ –8ppm/ oC. And the best breakdown strength(Eb~19kV/mm, with a sample thickness of 1 mm) was obtained under the sintering temperature of 1425 °C.In order to further improve the comprehensive properties of the(Mg0.9-yCayZn0.1)2(Ti0.99Mn0.01)O4 ceramics, and reduce the generation of the defects. In the fifth chapter, we mainly studied the effect of oxygen atmosphere sintering to the microwave dielectric properties and breakdown strength of these ceramics. The experimental results showed that, compared with sintered in air, under oxygen atmosphere sintered(Mg0.9-y Cay Zn0.1)2(Ti0.99Mn0.01)O4 ceramics(where y=0.03, 0.05) got little changed microwave dielectric properties, but had dramatically improved the breakdown strength(Eb~27 kV/mm, when y=0.03 with a sample thickness of 1 mm). Impedance spectroscopy analysis results showed that the resistivity of these ceramics sintered at oxygen atmosphere was increased obviously. O xygen atmosphere sintering is beneficial to improving the comprehensive properties of the(Mg0.9-yCayZn0.1)2(Ti0.99Mn0.01)O4 ceramics. |
PDF Full Text Request