高能球磨法制备Mg_4Nb_2O_9微波介质陶瓷及其表征

Preparation and Characterization of Mg_4Nb_2O_9 Microwave Dielectric Ceramics by Using High-energy Ball-milling Method

采用高能球磨法制备粉体,粉体球磨60h后在900℃保温3h预烧合成Mg4Nb2O9纯相,研究了由高能球磨所得粉体制备的Mg4Nb2O9陶瓷的相结构、显微组织和微波介电性能随烧结温度的变化关系。X射线衍射检测Mg4Nb2O9陶瓷在1150～1200℃烧结过程中有微量的MgNb2O6和Mg5Nb4O15杂相产生,烧结温度高于1200℃时,样品为Mg4Nb2O9纯相;样品收缩率和密度随烧结温度的增大而增加,在1200℃趋于饱和,分别为13.6和4.22g/cm3(相对密度96.42%);样品的气孔含量随烧结温度增大降低,晶粒尺寸随烧结温度增大而增大,介电常数和品质因数随烧结温度的增大而增加;1200℃烧结的样品具有高的致密度、清晰的显微组织,平均晶粒尺寸为3.5μm,微波介电性能εr=12.6,Q·f=133164GHz,τf=-56.69×10-6/℃。实验结果表明,高能球磨有效促进球磨后粉体在900℃低温合成Mg4Nb2O9纯相;并降低Mg4Nb2O9陶瓷的烧结温度到1200℃,改善了陶瓷的谐振频率温度系数,有望成为新一代中温烧结微波介质材料。

Mg4Nb2O9 powders were synthesized at 900℃ dwelling for 5h by using high-energy ball-milling method. The phase transition, sintering behavior, microstructures and microwave dielectric properties of Mg4Nb2O9 ceramics prepared from the milled powders were investigated. From the XRD, in samples sintered at 1 150-1 200℃, a minor of secondary phase of MgNb2O6 and Mg5Nb4O15 were found, and when sintered at 1 250℃, a single phase of Mg4Nb2O9 ceramics was obtained. The shrinkage and bulk densities of Mg4Nb2O9 ceramics increased with increasing the sintering temperature, and reached the saturation values of 13.6, 4.22 g/cm^3 at the temperature of 1 200℃, respectively. With increasing the sintering temperature, volumes of pores were reduced, and the grain size, dielectric constant and quality factor were increased. Mg4Nb2O9 ceramics sintered at 1 200℃ had a dense structure, clear microstructures, with grain size of 3.5 m, and outstanding microwave dielectric properties： εr=12.6, Q ·f=133164 GHz, τf=56.69 ×10^6℃. The calcining temperature of Mg4Nb2O9 powders and the sintering temperature of Mg4Nb2O9 ceramics could be effectively reduced by using high-energy ball-milling method, Furthermore, the temperature coefficient of resonant frequency τf was improved. Therefore, the microwave dielectric properties of medium-temperature sintered Mg4Nb2O9 ceramic prepared by the HEM method made it an appropriate candidate for applications.