Low‐Fire Processing of MicrowaveBNBT‐Based High‐k Dielectric withLi2O–ZnO–B2O3Glass

Abstract

The effects ofLi2O–ZnO–B2O3(LZB) glass addition on densification and dielectric properties ofBa4(Nd0.85Bi0.15)9.33Ti18O54(BNBT) have been investigated. At a given ratio ofZnO/B2O3, the glass softening point decreases, but the thermal expansion coefficient and dielectric constant increase with increasingLi2Ocontent in theLZBglass. With 10 vol%LZBglass, the densification temperature reduces greatly from 1300°C for pureBNBTto 875°C–900°C forBNBT + LZBdielectric, and the densification enhancement becomes more significant with increasingLi2Ocontent in theLZBglass. The above result is attributed to a chemical reaction taking place at the interface ofLZB/BNBTduring firing, which becomes less extensive with increasingLi2Ocontent in theLZBglass. Therefore, more residualLZBglass, which acts as a densification promoter toBNBT, is left with increasingLi2Ocontent. For theLZBglass with aLi2Ocontent in the range 10–30 mol%, the resulting 90 vol%BNBT + 10 vol%LZBmicrowave dielectric has a dielectric constant of 55–70, product (Q × fr) of quality factor (Q) and resonant frequency (fr) of 1000–3000 GHz at 5–5.79 GHz, and a temperature coefficient of resonant frequency (τf) of 10–60 ppm/°C in the temperature range between 25°C and 80°C.