LOW-TEMPERATURE SINTERED (ZnMg)₂SiO₄ MICROWAVE CERAMICS WITH TiO₂ ADDITION AND CALCIUM BOROSILICATE GLASS

B. Li, B. Tang, S. Zhang, H. Jiang

The low-temperature sintered (ZnMg)₂SiO–TiO₂ microwave ceramic using CaO–B₂O₃–SiO₂ (CBS) as a sintering aid has been developed. Microwave properties of (Zn_1-xMg_x)₂SiO₄ base materials via sol-gel method were highly dependent on the Mg-substituted content. Further, effects of CBS and TiO₂ additives on the crystal phases, microstructures and microwave characteristics of (ZnMg)₂SiO₄ (ZMS) ceramics were investigated. The results indicated that CBS glass could lower the firing temperature of ZMS dielectrics effectively from 1170 to 950°C due to the liquid-phase effect, and significantly improve the sintering behavior and microwave properties of ZMS ceramics. Moreover, ZMS–TiO₂ ceramics showed the biphasic structure and the abnormal grain growth was suppressed by the pinning effect of second phase TiO₂. Proper amount of TiO₂ could tune the large negative temperature coefficient of resonant frequency (t_f) of ZMS system to a near zero value. (Zn_0.8Mg_0.2)₂SiO₄ codoped with 10 wt.% TiO₂ and 3 wt.% CBS sintered at 950°C exhibits the dense microstructure and excellent microwave properties: ε_r = 9.5, Q·f = 16 600 GHz and t_f = −9.6 ppm/°C.

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