LOW-TEMPERATURE SINTERED (ZnMg)_2SiO_4 MICROWAVE CERAMICS WITH TiO_2 ADDITION AND CALCIUM BOROSILICATE GLASS

摘要

The low-temperature sintered (ZnMg)_2SiO_4-TiO_2 microwave ceramic using CaO-B_2O_3-SiO_2 (CBS) as a sintering aid has been developed. Microwave properties of(Zn_(1-x)Mg_x)_2SiO_4 base materials via sol-gel method were highly dependent on the Mg-substituted content. Further, effects of CBS and TiO_2 additives on the crystal phases, microstructures and microwave characteristics of(ZnMg)_2SiO_4 (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-TiO_2 ceramics showed the biphasic structure and the abnormal grain growth was suppressed by the pinning effect of second phase TiO_2. Proper amount of TiO_2 could tune the large negative temperature coefficient of resonant frequency (τ_j) of ZMS system to a near zero value. (Zn_(0.8)Mg_(0.2))_2SiO_4 codoped with 10 wt.% TiO_2 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 τ_f= -9.6ppm/℃.