Study On The Dielectric Properties Of Ba(Mg_1/3Ta_2/3)O₃ Microwave Ceramics

A ceramic Ba(Mg1/3Ta2/3)O3 (BMT) was known as one of the compound having the (A=Ba, Sr; =Mg, Zn; =Nb, Ta) complex perovskite structure. It was the most excellent representative of the low microwave dielectric ceramic materials, which can be developed as filters and resonators using in the microwave frequency area. But the sintering temperature of BMT was too high to about 1600℃, it can easily induce the volatilization of the Mg,Ta component and then deteriorate the dielectric properties. Therefore it is necessary to study on the BMT ceramic material with the propose to lower the sintering temperature and improve the dielectric properties.In this paper, two kinds of A-site and B-site substituted compound were studied, including their influence on the system sinterabality and dielectric properties. The relation between microstructure changing and its dielectric properties was also discussed.By the A-site substitution of Sr2+ ions for Ba2+ ions, a solid-solution compound (Ba1-xSrx)(Mg1/3Ta2/3)O3 (BSMT) was obtained which of complex perovskite structure. A new low-temperature phase had been found as Sr content x ≥0.6. This phase transformation was caused by the tilting of oxygen octahedral, and was clarified to have a lower symmetry structure compared with the hexagonal structure of BMT or SMT. The new low-temperature phase can decrease the sintering temperature of BSMT to 1500℃. The microstructure changing and the unconventional dielectric properties of BSMT was related with the low-temperature phase transformation.For the addition of BaSnO3 on (1-x)Ba(Mg1/3Ta2/3)O3-xBaSnO3 ceramic, B-site Sn4+ ions substituted for Mg2+ or Ta5+ ions. It was found that the sinterability of BMT ceramic could be greatly improved by the addition of BaSnO3. A dense BMT ceramic with 94.1% relative density could be obtained by the addition of 0.15wt% BaSnO3 sintered at 1500℃ for 3h. While the microwave dielectric properties were sensitively related with the density of the ceramics, the excellent properties were as follow: =24.9,Qf0=354,000,=0.