Studies On Molten Salt Approach And Low Temperature Sintering Of ZnO-TiO₂-based Microwave Dielectric Ceramics

In recent years, with the rapid development of microwave technology, microwave dielectric ceramics have become focal point of research rapidly all over the world. In order to reduce costs, and to meet the need of microwave circuit in integration and miniaturization, many countries have enlarged the research of new microwave dielectric materials with low sintering temperature. ZnO-TiO₂ ceramic materials of ilmenite structure has been considered to be a promising microwave dielectric materials, which has relatively low sintering temperature and excellent microwave dielectric properties. However, its further development were limited by narrow temperature range of ZnTiO₃(hexagonal) which is easily decomposed to Zn2TiO4 of low microwave dielectric properties. Pure ZnTiO₃ powders were prepared by molten salt methods in this article, and to reduce the sintering temperature of ZnO-TiO₂ ceramic by doping low melting point oxides.Phase-pure ZnTiO₃ powders were successfully prepared by molten salt methods, using ZnO and TiO₂ as raw materials in molten salt of NaCl-KCl. We investigated the effect of calcining temperature, holding time and mass ratio of salt to raw materials on the synthesis and micromorphology of ZnTiO₃ powders. The results show that ZnTiO₃ powders with good micromorphology can be obtained when the mass ratio of salt to raw materials is 1:1, and calcining temperature at 800℃for 1h. The grain growth is complete and exhibits a flake-like structure, and the as-produced powder is homogenous and has no obvious agglomeration. ZnO-TiO₂ ceramic sintered at 1100℃for 2h after preheated at 800℃could get a maximum bulk density, achieve 96.5% of theoretical density, and microwave dielectric properties were:εr≈25.3,Qf≈15200 GHz,Ï„f≈+36 ppm/℃。ZnO-TiO₂ ceramic sintered at different temperature, which doped with Li₂CO₃-B₂O₃,Li₂CO₃-B₂O₃-V2O5, and the behavior of sintering, phase composition, microstructure and microwave dielectric properties of ZnO-TiO₂ ceramic were characterized or measured by means of XRD, SEM. As a result, The bulk density ofZnO-TiO₂ ceramic doped with 2wt% addition of Li₂CO₃-B₂O₃ sintered at 930℃for 2h could get the maximum value 4.96g/cm³, achieve 96% of theoretical density, and microwave dielectric properties were:εr≈29.8,Qf≈11050 GHz,Ï„f≈+39ppm/℃. The bulk density of ZnO-TiO₂ ceramic doped with 3wt% addition of Li₂CO₃-B₂O₃-V2O5 sintered at 840℃for 2h could get a higher value 4.99g/cm³, achieve over 96% of theoretical density, and microwave dielectric properties were:εr≈24,Qf≈22900 GHz,Ï„f≈-4ppm/℃。...