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

Ba(Mg1/3Ta2/3)O-3 (BMT) ceramics have excellent microwave dielectric properties, but they are difficult to sinter because of their high sintering temperature of 1650 degrees C. However, in this study the addition of B2O3 to BMT ceramics enabled sintering to be performed at temperatures as low as 1300 degrees C. The BaB4O7 phase, which melts at approximately 900 degrees 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 (Er) 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 x f was explained by the presence of the Ba3Ta5O15 second phase. Excellent microwave dielectric properties of Q x f= 195,000 GHz, epsilon(r) = 24 and tau(f) = 4.74 ppm/degrees C were obtained by adding 0.5 mol% B2O3 to BMT ceramic and sintering at 1500 degrees C for 6 h. (c) 2006 Elsevier Ltd. All rights reserved.