Processing and microwave dielectric properties of barium magnesium tantalate ceramics for high-quality-factor personal communication service filters

A modified route, based on calcined MgO, Ta₂O₅, BaCO₃, and ZrO₂, was developed and used for preparation of barium magnesium tantalate (BMT) and barium zirconate (BZ)-doped BMT ceramics (BZ-BMT). The dielectric constant for BMT ceramics sintered at 1600 °C for 2 h was 24.9 at 7.28 GHz. The average long-range ordering parameter for undoped BMT ceramics was 0.81 ± 0.03 and the coresponding average quality factor and resonant frequench product (Q_d · f_o) was 147,000 ± 3800 GHz. A significant level of B-site long-range cation disorder was introduced as a result of BZ doping of BMT ceramics. The average ordering parameters for 3 and 4 mol% BZ-doped BMT were found to be 0.69 ± 0.06 and 0.49 ± 0.13, respectively. The decrease in ordering parameters did not lead to a dramatic decrease in the corresponding average quality factors of 3 mol% BZ-BMT (Q_d · f_o = 127,000 ±3800 GHz) and 4 mol% BZ-BMT (Q_d · f_o = 139,000 ± 4200 GHz). The results suggest that the B-site cation ordering is not a primary factor that influences the observed microwave loss in BMT ceramics. The influence of atomic level point defects, induced from raw material impurities, processing, etc., may be more important in controlling the quality factor of BMT ceramics.