Synthesis And Microwave Dielectric Properties Of ZnGa₂O₄ And ZnAl₂O₄-based Low-permittivity Ceramics

With the rapid development of modern communication technology, microwave dielectric ceramic materials with low dielectric constant and high quality factor have obtained more and more attentions from people; the researches of this field are also increasingly broad and deep. In view of the current research status of low-permittivity microwave dielectric ceramics, this paper synthesized Zn Ga2O4 and Zn Al2O4 low-permittivity ceramic materials, respectively using hydrothermal method and solid-phase method. O n the basis of various characterizations, such as XRD, SEM, TEM, HRTEM, SEAD, FFT, FT-IR, Raman, XPS and microwave dielectric performance analysis etc, to study the relationship among synthesis conditions, sintering temperature, phase composition, microstructure and dielectric properties.(1) Solution p H value, reaction temperature, reaction time and initial concentration have a significant effect on hydrothermal synthesis of Zn Ga2O4. Zn C l2·4H2O/Ga2O3 system can generate Zn Ga2O4 pure phase only under the condition of p H=7, T=250℃, t=1h, C(Zn C l2·4H2O)=0.04 mol/L. Furthermore, the reaction process could change the morphology of Zn Ga2O4 crystal. Zn Ga2O4 synthesized by hydrothermal method appears as cube sugar shaped nano self-assembly, with a certain degree of reunion. After adding dodecyl benzene sodium and ball mill for a long time, Zn Ga2O4 nano self-assembly structure will be destroyed, but the former can keep the small sphere particles in it, the latter will crush it thoroughly. Even though Zn Ga2O4 synthesized by solid-phase method then recrystallized utilizing hydrothermal method, its microstructure is still little change. In addition, the synthesis method of Zn Ga2O4 ceramic has a great influence on the microwave dielectric properties. Zn Ga2O4 ceramic sintered under 1500℃ has the following microwave dielectric properties: er = 9.93, Q×f = 73,000 GHz, τf =-68.7 ppm/℃, very different form that of ceramic synthesized by solid-phase method(er = 10.4, Q×f = 94,600 GHz, τf =-27 ppm/℃).(2) Compared with the doping effect of five kinds of sintering additives, including B2O3, Bi2O3, Cu O, 2Zn O·3B2O3, Li2CO3, it can be inferred that for Zn Al2O4 ceramic, 2Zn O·3B2O3 was the best, next is B2O3, Cu O and Bi2O3 in order, the last is Li2CO3. In fact, that’s why this article concentrates on the research of 2Zn O·3B2O3-Zn Al2O4 ceramic system. The single pure Zn Al2O4 phase existed when the amount of 2Zn O·3B2O3 was not more than 3 wt.%. FT-IR and Raman spectra were used to further elaborate the internal structure of 2Zn O·3B2O3-doped Zn Al2O4 ceramics. Zinc borate was effective sintering aid for Zn Al2O4 ceramics. It was able to not only improve the relative density markedly, but also enhance the quality factor significantly, while still maintain a low dielectric constant and stable temperature coefficient value. Specimens containing 3 wt.% 2Zn O·3B2O3 exhibited excellent microwave dielectric properties: er = 8.32, Q×f = 93, 600 GHz(at 14.0 GHz) and τf =-68.5 ppm/℃. They are promising candidates for microwave/millimeter-wave applications at high frequency.