| Currently, Ba (Mg 1/3Ta2/3) O3 and Ba (Zn 1/3Ta2/3) O3 are the main material used at high microwave frequency, which have excellent microwave dielectric properties but quite high price. In recent years, with the civilian microwave communications industry developing towards higher frequency extension, the price of material have to be cut down to meet the demand. Ba (Mg1/3Nb2 /3)O3 has the advantage of low prices , higher dielectric constant compared witn tantalate, and the highest theoretical quality factor va- lue among the series of niobate material, so it is the most promising microwave materials to replace of the tantalite for high-frequency application. But the quality factor value of Ba(Mg1/3Nb2/3)O3 is much lower than the theoretical value, and the temperature coeffieient of resonance frequency is a large positive number (= 33×10-6/℃). Otherwise, the sintering temperature (1550℃) of Ba(Mg1/3 Nb2/3) O3 without doped were quite high. Based on the theories and experimental results of research works on microwave dielectric ceramics, the methods of modifying Ba(Mg1/3 Nb2/3)O3 are put forward, which include the processing techniques, doping and two phase compositing.Processing techniques of Ba (Mg1/3 Nb2 /3)O3 ceramics was Studied, and the work researched effect of sintering system on the microstructure and microwave dielectric properties. The results show that, the appropriate pre-synthesis temperature plays a key role in guaranteeing the pure phase of Ba (Mg1/3Nb2/3)O3 ceramic. After sintering at 1550℃and annealing for 8h, the ceramics get a better microwave dielectric properties:εr= 33.5, Q×f= 52000,τf= 33×10-6/℃.The influence of low molten point additives CBS (Ca-B-Si), CuV2O6 and BiVO4 on the sintering behavior, microstructure and microwave dielectric properties of Ba (Mg1/3Nb2 /3)O3 ceramics was studied. The results show that:(1) CBS can low the sinter- ing temperature from 1500℃to 1250℃, and improve the microwave dielectric proper- ties. The B-site ordering degree increased with CBS addition increasing, and when CBS addition achieves 3wt%, Ba (Mg1/3Nb2/3)O3 gets the best microwave dielectric proper- ties:εr= 28, Q×f= 67800 (8GHz),τf= 45×10-6/℃. (2) CuV2O6 can effectively low the sintering temperature to 1075℃and promote the growth of grain. But the Q×f value was not significantly improved, and superfluous doping may cause microwave performance worsening rapidly. When CBS addition achieved 1.5wt%, Ba (Mg1/3 Nb2 /3) O3 gets the best microwave properties:εr=35, Q×f=54000,τf=-24×10-6/℃.(3) The sintering temperature drop from 1500℃to 1150℃~ 1175℃when BiVO4 doped in Ba (Mg1/3 Nb2/3) O3 ceramics. At 1.5wt% BiVO4, the specimen shows the best microwave properties:εr= 34, Q×f=63000GHz (8GHz),τf=27×10-6/℃.(1-X)Ba (Mgl/3 Nb2/3) O3·(X) MgTiO3 ceramics was prepared to modulateτf tow- ards zero. MgTiO3 has a large negative number of temperature coefficient of resonant frequency,According to the logarithmic mixing rule, moderate content of MgTiO3 added to Ba (Mg1/3 Nb2 /3) O3 can modulateτfto zero. Studies show that temperature coefficient move towards negative, when MgTiO3 content increased in the composite ceramics. When X = 0.45, near-zero temperature coefficient of resonant frequency is obtained. The microwave dielectric property is:εr= 24, Q×f=24000 (8GHz),τf=-1.2×10-6 /℃. |
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