Low‐Fire Processing of Microwave BNBT ‐Based High‐k Dielectric with Li 2 O – ZnO – B 2 O 3 Glass

The effects of Li 2 O – ZnO – B 2 O 3 ( LZB ) glass addition on densification and dielectric properties of Ba 4 ( Nd 0.85 Bi 0.15 ) 9.33 Ti 18 O 54 ( BNBT ) have been investigated. At a given ratio of ZnO / B 2 O 3 , the glass softening point decreases, but the thermal expansion coefficient and dielectric constant increase with increasing Li 2 O content in the LZB glass. With 10 vol% LZB glass, the densification temperature reduces greatly from 1300°C for pure BNBT to 875°C–900°C for BNBT  +  LZB dielectric, and the densification enhancement becomes more significant with increasing Li 2 O content in the LZB glass. The above result is attributed to a chemical reaction taking place at the interface of LZB / BNBT during firing, which becomes less extensive with increasing Li 2 O content in the LZB glass. Therefore, more residual LZB glass, which acts as a densification promoter to BNBT , is left with increasing Li 2 O content. For the LZB glass with a Li 2 O content in the range 10–30 mol%, the resulting 90 vol% BNBT  + 10 vol% LZB microwave dielectric has a dielectric constant of 55–70, product ( Q × f r ) of quality factor ( Q ) and resonant frequency ( f r ) of 1000–3000 GHz at 5–5.79 GHz, and a temperature coefficient of resonant frequency (τ f ) of 10–60 ppm/°C in the temperature range between 25°C and 80°C.