Microwave dielectric properties of low temperature sintered ZnWO4-TiO2 composite ceramics

The (1-x)ZnWO4-xTiO(2) composite ceramics were synthesized by the conventional solid-state method. The phase formation, microstructures, element composition and microwave dielectric properties of (1-x)ZnWO4-xTiO(2) composite ceramics and 0.75ZnWO(4)-0.25TiO(2) ceramics with Li2CO3-H3BO3 addition were investigated. Biphase structure of (1-x)ZnWO4-xTiO(2) composite ceramics sintered at 1160 degrees C/2 h was confirmed by using X-ray diffraction and the back scattering electron images. The dielectric constant Er and the temperature coefficient of resonant frequency tau(f) values of composite ceramics increased linearly with the increase of TiO2 phase. The tau(f) value of (1-x)ZnWO4-xTiO(2) was found to be dependent on phase composition, which is related to the amount of TiO2. When x is 0.25, the tau(f) value of (1-x)ZnWO4-xTiO(2) was near 0 ppm/degrees C. With small amount of Li2CO3-H3BO3 addition, the sintering temperature of composite ceramics was further reduced to below 950 degrees C from about 1100 degrees C without obviously deteriorating the microwave dielectric properties, and the tau(f) values could be adjusted with the Li2CO3-H3BO3 content. The 0.75ZnWO(4)-0.25TiO(2) ceramics with 5.0 wt% Li2CO3-H3BO3 sintered at 950 degrees C/2 h exhibited good microwave dielectric properties of epsilon(r)=18.99, Q x f =13,517 GHz and tau(f)=-11.44 ppm/degrees C. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.