Effect of grain size and secondary phase on microwave dielectric properties of Ba(Mg1/3Ta2/3)O-3 and Ba([Mg,Zn](1/3)Ta-2/3)O-3 systems

Here we report the influence of the grain size of the Ba(Mg-1/3,Ta-2/3)O-3 (BMT) and secondary phase formed in Ba([Mg0.8Zn0.2](1/3),Ta-2/3)O-3 (BMZT) ceramics on the microwave dielectric properties. BMT and BMZT ceramics were prepared by conventional mixed-oxide reaction method using high purity reagents. Samples with different grain size and secondary phase content were obtained by controlling the sintering time of the BMT and BMZT. The secondary phase comprised of BaTa2O6, which includes small amount of Zn, was formed due to the vaporization of ZnO from BMZT by the high temperature sintering. The Qf value of BMT increased up to 400 THz with increasing the grain size of ceramics, whereas the Qf value of BMZT decreased with increase of the BaTa2O6 content. This second phase also caused an increase in the temperature coefficient of the resonant frequency of BMZT. (c) 2005 Elsevier Ltd. All rights reserved.