The effect of glass additives on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

The effect of glass additives on the densification, phase evolution, microstructure and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 (BMT) was investigated. Different weight percentages of quenched glass such as B2O3, SiO2, B2O3-SiO2, ZnO-B2O3, 5ZnO-2B2O3, Al2O3-SiO2, Na2O-2B2O3.10H2O, BaO-B2O3-SiO2, MgO-B2O3-SiO2, PbO-B2O3-SiO2, ZnO-B2O3-SiO2 and 2MgO-Al2O3-5SiO2 were added to calcined BMT precursor. The sintering temperature of the glass-added BMT samples were lowered down to 1300 deg. C compared to solid-state sintering where the temperature was 1650oC. The formation of high temperature satellite phases such as Ba5Ta4O15 and Ba7Ta6O22 were found to be suppressed by the glass addition. Addition of glass systems such as B2O3, ZnO-B2O3, 5ZnO-2B2O3 and ZnO-B2O3-SiO2 improved the densification and microwave dielectric properties. Other glasses were found to react with BMT to form low-Q phases which prevented densification. The microwave dielectric properties of undoped BMT with a densification of 93.1% of the theoretical density were εr=24.8, τf=8ppm/oC and Quxf=80,000GHz. The BMT doped with 1.0wt% of B2O3 has Quxf=124,700GHz, εr=24.2, and τf=-1.3ppm/ deg/ C. The unloaded Q factor of 0.2wt% ZnO-B2O3-doped BMT was 136,500GHz while that of 1.0wt% of 5ZnO-2B2O3 added ceramic was Quxf=141,800GHz. The best microwave quality factor was observed for ZnO-B2O3-SiO2 (ZBS) glass-added ceramics which can act as a perfect liquid-phase medium for the sintering of BMT. The microwave dielectric properties of 0.2wt% ZBS-added BMT dielectric was Quxf=152,800GHz, εr=25.5, and τf=-1.5ppm/ deg. C