Synthesis, processing, and microwave dielectric properties of barium zinc tantalate (Ba(Zn(1/3)Ta(2/3))O(3)) ceramics for wireless communications

The relationships between the composition, processing, microstructure, and microwave dielectric properties of barium zirconate (BaZrO3) doped barium zinc tantalate (Ba(Zn_1/3Ta_2/3)O₃) (BZT) ceramics were investigated. A conventional mixed oxide route was used to prepare undoped and doped (4 mol% of BaZrO₃) BZT ceramics. Undoped BZT ceramics with over 96% theoretical density were obtained by sintering for 32 hours in a ZnO atmosphere. In contrast, undoped BZT ceramics sintered in air resulted in very low levels of densification (∼78%). One of the important conclusions of this study is that BaZrO₃ additions were shown to enhance the densificadon of BZT ceramics, in both air and ZnO atmospheres. The average density of the barium zirconate doped BZT ceramics sintered at 1450°C for 2 hours in both sintering atmospheres was about 96%. The average Q_df_o value for undoped BZT sintered 1450°C for 2 hours in air was 32,200 ± 1100 GHz, while the average density was 77.1%. The lower Q_d f_o values were attributed to the presence of water vapor in the pores of the ceramic microstructure. The average Q_d f_o value of BaZrO₃ doped BZT ceramics sintered under identical conditions was 135,600 ± 2800 GHz and the average density was 96.6%. One important conclusion of this study is that the enhancement of Q_df_o value of BZT ceramics may be linked to the enhancement of densification kinetics and the level of density achieved and also perhaps to the point defect chemistry changes introduced by doping and/or occurring during sintering. Consistent with prior reports, BaZrO3 doping was shown to cause a considerable decrease in the long-range ordering (LRO) of B-site cations as detected by x-ray diffraction (XRD). Our findings reported here show that, contrary to the line of thinking emphasized in much of the prior literature, the long-range ordering B-site cations may not be a predominant factor that controls the Q_df_o of such microwave dielectrics as WT. This work shows, quantitatively, that the level of densification and uniformity of dopant concentrations has a significant influence on the observed Q_df_o values of BZT ceramics.