Preparation And Characterization Of BaO-TiO₂ Microwave Dielectric Powders

The Ba₂Ti₉O₂₀ and BaTi₄O₉ material which have superior microwave dielectric properties have became classic and hot spot material in the field of microwave dielectric material, and they have been used to fabricate components working at high frequency such as resonators, filters and antennas. However, there are two inevitable problems in the synthesis of Ba₂Ti₉O₂₀ and BaTi₄O₉ using solid state reaction method: low formation of phase and high calcining and sintering temperatures (-1400℃). The wet chemical method can visibly enhance the formation of Ba₂Ti₉O₂₀ and BaTi₄O₉, and lower the synthesis temperature. However, the wet chemical methods which have been developed are very complex and could not be controlled with ease, plus, some methods need additional devices and the raw materials are very expensive. Therefore, it is an emergent task to develop new and relatively simple method. In this study, low temperature synthesis of Ba₂Ti₉O₂₀ and BaTi₄O₉ have been achieved using cheap Ti(OC₄H₉)₄ and Ba(CH₃COOH)₂ as raw materials via a simple citric acid method in non-aqueous solution. The influences of various calcining processing on the sintering properties, microstrutures and dielectric properties were studied. The SnO₂ and ZrO₂ were used as dopants to lower the synthesis temperature further. The optimal processing conditions and dielectric properties were achieved. The contents of study include:The study on the conditions of low temperature synthesis of BaO-TiO₂ system powders by two steps calcining procedure. To overcome shortcomings of other wet chemical methods, two steps calcining procedure were used to synthesis single phase Ba₂Ti₉O₂₀ and BaTi₄O₉ via citric acid gel method. The conditions of obtaining clear and stable gel were studied. After two steps calcining processing, single phase Ba₂Ti₉O₂₀ and BaTi₄O₉ were obtained.The study on the effects of various calcining processing on sinterablity, microstructures and dielectric properties of BaO-TiO₂ system ceramics. The sinterablity, microstructures and dielectric properties of powders after second step calcining at 1200℃ were better than that of powders after first step calcining at750℃ and 900℃. The best dielectric properties obtained were as follows: Ba₂Ti₉O₂₀ sintering at 1250℃ for 4h, ε_r=38.4, Q×f =19320 GHz(at 4.6GHz), Ï„_f=8.7ppm/℃; BaTi₄O₉, sintering at 1250℃ for 4h, ε_r = 36.33, Q×f =28100 GHz(4.6GHz), Ï„_f=16.2ppm/℃The study on the characteristic of in situ SnO₂, ZrO₂ doped Ba₂Ti₉O₂₀. The in situ doping of SnO₂, ZrO₂ could further lower the synthesis temperature to 1100℃. The addition of SnO₂ and ZrO₂ greatly enfluenced the dielectric properties of ceramics. After sintering at 1200℃ for 4h, the best microwave dielectric properties achieved were: SnO₂ doped Ba₂Ti₉O₂₀, ε_r=37.01, Q×f=20010 GHz (at 4.6GHz) , Ï„_f =8.6ppm/℃; ZrO₂ doped Ba₂Ti₉O₂₀, ε_r=37.46, Q×f=20540 GHz (at 4.6GHz), Ï„_f =6.3ppm/℃...