Low-fire processing of microwave BaTi4O9 dielectric with crystalline CuB2O4 and BaCuB2O5 additives

The effects of interfacial reaction of CuB2O4 (CB)/BaTi4O9 (BT4) and BaCuB2O5 (BCB)/BaTi4O9 (BT4) on densification, phase development and dielectric properties of BaTi4O9 (BT4) have been investigated. With BaO present, the wetting of BCB/BT4 improves significantly in comparison to CB/BT4 at temperatures below 925 °C. However, the enhancement in densification becomes less significant for BCB+BT4 than that of CB+BT4 at reduced temperatures. The above results are attributed to a chemical reaction taking place at the interface of CB/BT4 and BCB/BT4 during firing, which becomes less extensive with BaO present in the sintering promoter. For both CB+BT4 and BCB+BT4 systems, the resulting composites have a dielectric constant of 36–40, product (Q·fr) of quality factor (Q) and resonant frequency (fr) of 13,000–21,000 GHz, and a temperature coefficient of resonant frequency (τf) of 20–40 ppm/°C in the temperature range of 25–80 °C.