Effect of B2O3 on the microstructure and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

Ba(Mg1/3Ta2/3)O3 (BMT) ceramics have excellent microwave dielectric properties, but they are difficult to sinter because of their high sintering temperature of 1650 °C. However, in this study the addition of B2O3 to BMT ceramics enabled sintering to be performed at temperatures as low as 1300 °C. The BaB4O7 phase, which melts at approximately 900 °C, may have been responsible for the decrease of the sintering temperature. The presence of Ba3Ta5O15 second phase was observed in the BMT ceramics containing a large amount of B2O3. The relative density and dielectric constant (ɛr) were considerably increased with the addition of a small amount of B2O3. The Q-value was also increased when a small amount of B2O3 was added, but was decreased when the B2O3 content exceeded 0.5 mol%. The decrease of Q × f was explained by the presence of the Ba3Ta5O15 second phase. Excellent microwave dielectric properties of Q × f = 195,000 GHz, ɛr = 24 and τf = 4.74 ppm/°C were obtained by adding 0.5 mol% B2O3 to BMT ceramic and sintering at 1500 °C for 6 h.